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Radio Paging System Basics

PAGING SYSTEM OVERVIEW

(Source: Motorola, author unknown.)

1.0 PAGING INTRODUCTION
Paging is a one-way communications system. Paging allows callers to forward information to anyone with a pager and within the system coverage boundaries. System users can directly page people via the telephone system or through a dispatch message center. Paging information will be either, a tone only page, a voice page or a display page. A tone only page refers to the user being alerted with no information following. The alert inherently implies that the user should call some predetermined number to retrieve messages or information that awaits. This type of paging is very specific and mainly used by dispatch services. A voice page allows the user to send a finite length speech message directly from any telephone to the pager. This type of paging is quite useful since it is easy to use and requires no special equipment besides a telephone. The paging system alerts the subscriber and delivers a direct and to the point message where a return call is not necessary. This service is popular in hospital environments where time is crucial and a direct outbound message is sent to a paging user. This type of service however has potential draw backs since it uses up much system air time, receiver audio quality can be poor in some coverage areas making the message difficult to hear or it can be difficult to hear if received in a high noise environment. Display paging refers to the user receiving either numeric or alpha numeric information on an LCD display. Numeric display is the most popular because it is easy to access from any touch tone phone system and air time usage is lower. The user can only enter return phone numbers or some special numeric codes defined specifically by individual users. Alphanumeric display paging allows the user to send text messages. This requires special data entry equipment (typically operator-dispatched). The system operator and pager model determine alphanumeric message lengths. Alphanumeric is growing in popularity however it requires maximum air time and data entry services.

Two pieces of information that determine the paging message are the individual pager address (cap code) and the actual information to be sent to the pagers. Pager addresses and paging information can exist in two forms, either analog or binary. An analog transmission refers to a paging receiver receiving a signal on the paging transmit carrier frequency and demodulating audio tones or voice transmissions. A binary transmission differs from an analog transmission in the sense that the receiver looks for frequency shifts above and below the carrier and never has to lock on to the transmit carrier frequency. This type of transmission is referred to as Frequency Shift Keying Non Return to Zero, or FSK-NRZ for short. These shifts above and below the carrier correspond with the binary number system of ones and zeros. In this manner we can transmit and receive data based directly on the binary number system. Another parameter of importance for binary transmissions is the information transmission speed, often referred to as the baud rate. The baud rate is typically denoted by units of bits per second, where a bit is a binary one or zero. The greater the baud rate number, the faster the transmission speed and the less system air time needed to transmit the desired paging information.

1.1 ANALOG PAGER ADDRESSING MODES
Several analog and binary coding formats exist for addressing pagers. The analog addressing coding formats in use today are Two-Tone or 5-Tone/6-Tone Decimal Digit. The Two-Tone coding format uses a total of 110 tones ranging from 67 to 2468.5 Hz and has a maximum capacity of 3540 unique codes. As the name implies two-tone bursts of specified duration are transmitted sequentially to alert a pager. The plan supports both tone and voice pagers, and tone only pagers. The plan also has provisions for group calling, the ability to alert several pagers simultaneously and battery saver capability. Battery Saver operation typically refers to the pager's ability to cycle from a low current draw state and the normal current draw state and still receive pages. Pager address alert times for Two-Tone coding formats can range from 2.5 seconds for tone-only pager to 5.3 seconds for tone and voice pagers. Group call pages can take up to 10 seconds. The Two-Tone coding format has limited user capacity and paging throughput can become an issue due to long alert times on a busy channel.

The 5-Tone/6-Tone Decimal Digit coding format supports tone and voice pagers however this coding format can alert pagers much faster than the Two-Tone coding format. The 5-Tone/6-Tone coding format uses 12 separate frequency tones to represent the decimal digits 0 through 9, a repeat number tone (R), and a special Tone X function. Each pager address is made up of 5 digits represented by the respective frequency tone burst. The tone bursts are sent sequentially, 33 milliseconds in duration each. A sixth tone burst is used for multiple addressing applications, hence the name 5/6 tone signaling. The 5-Tone/6-Tone coding format can support 100,000 subscribers. A typical 5/6 tone page takes approximately .217 seconds to alert the pager, a 12 times improvement over a standard Two-Tone page of 2.5 seconds.

1.2 BINARY ADDRESSING AND DATA CODING FORMATS
Several binary coding formats exist for pager addresses and numeric or alphanumeric display information. The industry predominant binary coding formats are Golay Sequential Coding, referred to as GSC, and Post Office Code Standardization Advisory Group, referred to as POCSAG. GSC as we know it today, was expanded from what was known as the ECHO code format that supported 400,000 codes with 4 address capability per pager. GSC development from ECHO code involved improved battery saver operation, improved efficiency, and increased code capacity of 1 million codes with 4 address capability per pager. The GSC signaling scheme is an asynchronous scheme that transmits pager address information at 300 baud and display data at 600 baud. The GSC binary coding format provides error correction for the pager address and display information. A typical "display page" address alert takes .2 seconds for a non-battery saver pager and .24 seconds for a battery saver pager. The GSC code is an extremely robust code at an adequate signaling speed offering substantial resistance to falsing.

The POCSAG coding format was primarily invented to improve signaling speed thereby increasing system throughput. The POCSAG coding format has an increased code capacity of 2 million codes with 4 addresses per pager. Unlike GSC which is asynchronous, POCSAG employs bit synchronization and word framing. POCSAG uses time division for battery saver operation whereas GSC relies on selective batching. POCSAG signaling operates with both address and data at the same baud rate, initial offering at 512 baud. Improvements in equipment technology have increased the POCSAG signaling speed to 1200 and 2400 baud. At a 512 baud rate POCSAG address alerts take .0625 seconds. This a 3 times improvement over the GSC signaling scheme. The structure of the POCSAG coding format allows for substantial system throughput performance. It is, however less immune to falsing than GSC signaling. POCSAG can correct 2 of 32 bits for address words and 1 of 32 for data words, whereas GSC can correct 3 of 23 bits for address words and 16 of 120 bits for data words. Depending on the desired system capacity, throughput, coverage and immunity noise the system operator can decide which binary code format best suits there needs. More detailed information regarding analog and binary coding formats can be found in Motorola PAGING FORMAT GUIDE publication # TBD.

1.3 PAGING SYSTEM TYPES: NON-SIMULCAST vs. SIMULCAST
Paging systems are commonly referred to as being one of two types, either Simulcast or Non-Simulcast. Non-Simulcast systems are primarily for single transmitter systems or systems where coverage is not required to be continuous over a geographic coverage area, i.e. the transmitters are so far apart that they cannot interfere with each other. Non-Simulcast systems allow for lower transmitter costs since system alignment and maintenance for overlapping transmitter coverage is not an issue by definition.

A Simulcast Paging system refers to a system where coverage is continuous over a geographic area serviced by more than one paging transmitter. In this type of system the pager can be receiving signals from two or more paging transmitters when in the overlap area of the two or more paging transmitter. The overlap are of two or more paging transmitters is referred to as the non-capture are since a pager not locked or captured by a single transmitter. The construction of Simulcast System takes advantage of the overlapping transmitters signals in a constructive manner so that coverage is improved and the system can provide continuous coverage over a wide geographic area. This is accomplished during system optimization by delaying the signals from the transmitters that have overlapping coverage such that the signal arrives at the same time in the overlap area. This delay criterion is of great importance for binary paging. For analog paging additional signal qualities of phase and gain must be optimized for overlapping transmitters. A properly designed and optimized simulcast system will utilize the effects of overlapping transmitters to improve coverage and ensure that the audio and binary transmissions from all transmitters are of the highest possible quality and the signals arrive in the overlap area at exactly the same time from the pagers point of view. These Simulcast system constraints therefore dictate the transmitter hardware to be more precise and of tighter tolerance from one transmitter to the other. The frequency band and type of paging supported by the system will determine the amount of transmitter stability required reflected in additional transmitter hardware and cost. With the Simulcast System comes the need for increased system monitoring for changes and the ability of the system to compensate for changes that will degrade performance.

1.4 SECTOR PAGING
A paging system, either simulcast or non-simulcast, can be operated in either an, all transmitters key or a subset of all transmitters key, depending on the pager being paged. When all transmitters do not key for paging in the system this is referred to as sector paging. Sector paging allows the system operator to partition his system and charge various monthly service fees depending on the users desired area of coverage. The paging terminal database must now segregate and group page requests for various service areas. Customer billing also becomes a bit more involved since a variety of rates will be charged to customers. The only cost savings for this type of system operation is a savings in electricity for all the stations that do not always key. Sector paging provides no increase in system paging throughput, but in fact can even reduce throughput slightly since the base stations must be selectively keyed and de-keyed depending on the page requests. Efficient page request batching may not be possible if the page requests are not all associated with the same sector. Through the years sector paging has fallen off in popularity with the increase in users on a system. Most paging providers have been able to exploit the economies of volume and provide service to users at a reasonable fixed rate, determined by the page type, tone only, voice, numeric display or alphanumeric display, as opposed to the geographic coverage areas. In this manner all transmitters key and pass pages optimally with a minimum of time wasted keying and de-keying transmitters. Optimal service is provided when the system is a binary only, tone only and numeric display system. This has been the industry trend due to cost, customer demand, and reasonable service throughput. Throughput refers to the time the page is received by the pager versus the time when the page was input as a request to the system. The system goal is to service pages as fast as possible. Alphanumeric display is gaining popularity and commands a premium service cost due to the required system usage time and the need for data entry and dispatch services.

1.5 MULTIPLE FREQUENCY PAGING
Multiple frequency paging on a system is possible however it provides no benefit to service. When the multiple frequency transmitter is keyed on a channel the other channel is forced to be idle by definition. The objective of a paging system operator is to build a single frequency channel and load the channel to capacity such the system users receive acceptable paging throughput at a reasonable cost. If the system loading is excessive then throughput during peak paging hours may become unacceptable by users and service may be sought by the user from the competition. Typically multiple frequency paging is used when the user desires to hold a paging frequency they have been granted however they do not have the capitol to build a complete second system.

1.6 PAGING SYSTEM BLOCK DIAGRAM AND COMPONENTS
A paging system is composed of the following 6 basic elements (see Figure 1 below). Note: For very simple systems with limited capabilities, the Controller (2) and Communications Link (5) are not required to build a system that can page pagers. An example of this is a Tone Remote Control system. Tone Remote Control supports individual station keying for testing but does not support diagnostics whereby the stations communicate status and alarm information to the controller. In addition, for TRC systems the controller is optional since the TRC audio control sequence has been licensed to most paging terminal manufacturers and the terminal can generate the required tone bursts for key control. Any systems that support transmitter diagnostics and system maintenance will always require a controller (2) and some form of Communications Link (5) from the transmitters to the controller.

1) Paging Terminal

2) Controller

3) Outbound control and paging information channel

4) Transmitter network

5) Communications link from transmitter network to controller

6) End user pagers

figure 1

FIGURE 1. Paging System Block Diagram

OPERATIONAL DESCRIPTION OF THE 6 BASIC PAGING SYSTEM ELEMENTS

1) THE PAGING TERMINAL
The Paging Terminal maintains subscriber pager type and service information. The terminal accepts paging requests via direct dial-up phone interface or via data entry equipment. The terminal prepares the paging information for transmission and communicates to the controller that it needs access to the infrastructure. Terminals can also provide statistics on paging traffic and billing information. The paging terminal is connected to the controller for key requests and control handshakes as well as passing pager address and information for transmission. The terminal and controller are therefore co-located to allow for control signal and audio interface. The paging terminal provides user access typically by a Video Display Terminal (VDT) for database programming and review purposes. Terminals can usually support a variety of peripherals such as disk drives, printers, and modems for expanded user capabilities.

2) THE CONTROLLER
The controller is the central focal point of the system responsible for recognizing paging terminal requests and keying the transmitters in the proper paging mode, analog or binary. The controller, depending on its sophistication, is responsible for monitoring transmitter operational performance as well as reporting system level alarms. The controller can also perform system level maintenance to compensate for changes in the outbound control and paging information channel. Depending on the type, the controller may or may not store transmitter configuration and operational data, as well as logging station and system alarm information. The controller provides user access typically by a Video Display Terminal (VDT) for database programming and review. More sophisticated controller usually support a variety of peripherals such as disk drives, printers, and modems for expanded user capabilities.

3) THE OUTBOUND CONTROL AND PAGING INFORMATION CHANNEL
The outbound control and paging information channel is the medium by which the controller information is passed on to the transmitters. The most conventional information distribution methods are Radio Frequency RF) Links , dedicated wire lines to each transmitter from the controller site, or satellite up link and down links. With an RF link system the controller audio is sent to a Link transmitter via a wire line connection. A link repeater could then be used to listen to the link transmitter to further extend transmission of the information, hence the name repeater. With a wire line system the controller audio is sourced to a data splitter which then feeds the signal to each transmitter via a dedicated wire line. With a satellite distribution system the controller information is sent to the satellite up link location. Each station is equipped with a satellite dish and receiver to recover the controller information.

4) TRANSMITTER NETWORK
The paging base stations decode control information from the controller for keying in the appropriate mode, analog or binary. The transmitter network in conjunction with the antenna system converts the information from the paging terminal into modulation and RF energy for transmission to the paging receivers. The transmitters continually check their operating performance and generate alarms in the event of a degradation in performance. The controller and system configuration determine how and when the alarms are reported.

5) COMMUNICATIONS LINK
The communications link is primarily a feedback path from the transmitter network to the controller. This communications link is used to transfer base station status and alarm information from the transmitter network to the controller for evaluation and reporting. Several communications links may exist from the transmitter network to the controller. The communications link can be a one way path from base station to controller or a bi-directional depending on the type of link used. Some common communications links include dedicated wire lines, dial-up phone lines, and monitor receivers with dedicated return phone lines.

6) PAGERS
The pager is a specialized miniature radio receiver carried by the user for retrieval of information from the paging terminal. Depending on the pager and system, the user can receive either an alert, a voice transmission, a numeric display page, or an alpha numeric display page. The pager is only able to receive pages within the allowable coverage area provided by the transmitter network.

BASE STATION CONTROL METHODS

2.0 TONE REMOTE CONTROL
Tone Remote Control (TRC), is a Motorola control sequence used in keying transmitters. Three basic elements make-up the TRC sequence, namely High Level Guard Tone (HLGT), Function Tone (FT), and Low Level Guard Tone (LLGT). The TRC sequence follows an audio level convention whereby FT is 10 dB below HLGT and LLGT is 30 dB below HLGT. The relative audio levels of HLGT, FT, and LLGT are usually referenced to a system Test Tone level. Test tone is defined as a 1000 Hz signal sent from the controller at the system operating level by which the transmitters are aligned to produce nominal analog transmit deviation. Relative to Test Tone, HLGT is 5 dB above Test Tone, FT is 5 dB below Test tone and LLGT is 25 dB below Test tone. Figure 2. PURC TRC Sequence graphically illustrates the control sequence.

Paging uses a Tone Remote Control sequence called PURC TRC. PURC is an acronym for Paging Universal Remote Control. The above mentioned TRC sequence was modified and redefined to allow for keying a transmitter on a specific frequency channel as well as putting the transmitter in the proper mode of operation, analog or binary. The mode of transmitter operation is determined by the information which follows the TRC sequence. The analog mode is assumed when the normal TRC sequence of HLGT, FT, and LLGT is sent. The binary mode of operation is entered when no LLGT follows the FT, but instead a gap or pause of silence occurs followed by paging modem tones. The detection of silence can sometimes be falsed on a noisy control channel thereby making mode switches from analog to binary not possible. Consequently the binary page goes out in the analog mode and the pager is not alerted.

HLGT is a 2175 Hz. frequency tone which indicates the start of a TRC control sequence. Function Tone is used to tell the transmitter on what frequency channel to key or is used to disable a transmitter when sector paging is used. FT values range from 750 Hz. to 2350 Hz. in 100 Hz. steps. The 1950 Hz. function tone is the standard key on channel 1 frequency. LLGT is a 2175 Hz. tone used to let the base station know that the controller has access of the channel in the analog mode. A loss of LLGT and activity by the base station for more than 350 milliseconds will cause the transmitter to drop off the air. For more in depth timing information on the operation of PURC TRC consult the PURC Simulcast System Controller and Paging Station Controller instruction manual, part number 6881063E15.

Non-Simulcast Function Tone Key Commands for PURC 5000 stations. This option requires special TRC software and the transmitter needs to be programmed for multiple frequency operation.

2050 Monitor 1150- Key on Channel 5

1950 Key on Channel 1 1050- Key on Channel 6

1850 Key on Channel 2 950 - Key on Channel 7

1350 Key on Channel 3 750 - Key on Channel 8

1250 Key on Channel 4

Simulcast Station Function Tone Key Commands Standard PURC 5000 station TRC.

1950 Key on Channel 1

850 Key on Channel 2

2350 Key on Channel 3

Figure 2

FIGURE 2. PURC Tone Remote Control Audio Flow Diagram

2.1 DIGITAL REMOTE CONTROL
Digital Remote Control, DRC for short, is a Motorola developed MSK, Minimum Shift Keying, communications control scheme. The digital signaling scheme uses Cyclical Redundancy Checking (CRC) and convolutional coding. This provides excellent error detection and forward error correction in the presence of fading, noise, and multi-path distortion in the outbound (control) and inbound (diagnostic) RF channel. The code was developed by the Motorola Data Communications group and therefore the code is referred to as MDC. The signaling scheme used for Paging DRC control is a 1200 baud scheme, hence the name MDC 1200. The signaling scheme is transmitted via modem tones of 1200 and 1800 Hz. tones, for distribution through phone line and RF mediums. An MDC 1200 message used for paging control is approximately 233 milliseconds in duration.

Unlike TRC, which had limited control functionality, DRC is able to transfer much more information in each transmitted packet of MDC 1200. Due to error detection and correction, DRC offers substantial reliability in performance over TRC in noise environments. Unlike TRC which relied on "pauses" and "gaps" of silence to force mode switches, DRC simply sends a specific message identifying the desired mode of operation. DRC is therefore referred to as a positive control scheme. See Figure 3 and 4 below which illustrate Analog and Binary DRC keying sequences. The sequences shown are for single key and de-key modes. If multiple and alternating key requests were present the de-key message would be substituted with the appropriate MDC keying message. HLGT does not need to be resent since the link will remain keyed on activity.

ORIGINAL DRC CONTROL INFORMATION FLOW AND RELATIVE LEVEL DIFFERENCES

Figure 3

FIGURE 3. Analog and Binary keying sequence for Non-Advanced Control DRC Paging Stations

Figure 3 illustrates the order of control information as well as relative level differences in the information. As shown above HLGT is only required for a RF control system. HLGT is used for keying link transmitters and repeaters. The duration of HLGT is dependent on the number of repeaters and if DPL is used or not. See the section on page RF Distribution Channel for details. The MDC DRC messages are sent at the same level as HLGT. LLGT is sent only during an analog page as a positive qualifier for being in the analog mode. The base station looks for LLGT and will drop off the air if LLGT is not detected for more than 6 seconds and no audio activity exists. This is required as a fail safe in the event of a control channel impairment to the station, i.e. receiver, link transmitter, or link repeater failure, prior to decoding an MDC de-key message. With out this fail safe the station could remain keyed indefinitely with dead or offset carrier. LLGT is transmitted 30 dB down from HLGT and MDC audio level. The base station will notch filter the LLGT signal another 30-40 dB to prevent the tone from mixing with a voice page and degrading the audio quality. For an Analog transmission the audio is sent at 5 dB down from HLGT and MDC audio level. For a binary page LLGT is not sent. After a binary key message, FSK modem tones are sent until no more binary pages exist. The station senses FSK audio and will drop off the air if FSK audio is not detected for more than 6 seconds. This check of incoming FSK audio is a fail safe to prevent a transmitter from being keyed indefinitely if the control channel to the station is impaired, i.e. receiver, link transmitter, or link repeater failure, prior to decoding an MDC de-key message. The FSK modem tones are sent 5 dB down from HLGT and MDC audio level.

ADVANCED CONTROL DRC INFORMATION FLOW AND RELATIVE LEVEL DIFFERENCES

Figure 4

FIGURE 4. Analog and Binary keying sequence for Advanced Control DRC Paging Stations

Advanced Control Paging Stations are designed with a different hardware and software architecture than non-advanced control paging stations. This architecture difference imposes some operating differences in the MDC audio level required for optimal station MDC decoding. The only difference between Figure 3 and Figure 4 is the MDC message level relative to HLGT and paging information audio. MDC audio is 5 dB below HLGT. MDC audio level now is at the same level as either analog or binary paging information. In the event a DDC controller is used with Advanced Control Paging Stations, the MDC audio level from the Digital Diagnostic Controller (DDC) should be decreased by 5 dB. This 5 dB reduction in level gives the station additional high end head room. Non-Advanced control stations working under this audio level protocol will be more susceptible to falsing low deviation alarms since the alarm trip point is fixed in hardware and will alarm when MDC is received at 6 dB below the HLGT level. This only gives the channel 1 dB of margin as opposed to 6 dB.

2.2 DRC MESSAGE STRUCTURE AND FORMAT TYPES
DRC signaling allows for information transfer between the controller and transmitter as well as providing keying control. This added level of communications allows for remote individual transmitter access for diagnostics as well as configuring or reprogramming various station operating parameters. As with any communications protocol, the data is formatted and interpreted from a data set which is defined by the development product group. DRC as we know it today has two completely different data sets. These two differing data sets are commonly referred to as DRC 1 and DRC 2. Due to the limited amount of communications provided by DRC 1, DRC 2 was created to add expanded communications capability.

2.3 DRC 1
DRC 1 is the communications protocol used by the Digital Diagnostic Controller (DDC), Advanced Simulcast Controller 1000 (ASC 1000), PURC 5000 DRC transmitters (JLB models) and Micor DRC transmitters (non-Advanced Control). Advanced Control transmitters can support DRC 1 messaging however full feature capability of the Advanced Control can only be realized when DRC 2 messaging is used.

To better understand DRC 1 communications for key control and diagnostic messaging the following three DRC parameters must be discussed, namely, the System ID, the Group ID, and the Individual Station ID. The System ID has 255 possible values, ranging from 0 to 254. The System ID uniquely associates a paging transmitter with a DRC controller. The controller and paging transmitter must be programmed with matching System ID's if they are to communicate. Key control for paging is based on the System ID alone.

The Group ID is another ID used to differentiate the controller from the base station. The Group ID has 1024 possible values, ranging from 0 to 1023. The Group ID was implemented early on in the DRC development program for potential future expansion, however it has never been utilized. The Group ID is set by hardware jumpers on the DRC CPB board, unlike the System ID which is programmed in EEPROM non-volatile memory. A peculiarity between the Group ID and DDC controller does exist however. During diagnostic messaging, the station responses include the status of the CPB board Group ID. If the Group ID does not match the Group ID programmed in the DDC, then the message is ignored. This often creates a problem when someone accidentally changes the DDC Group ID value and then cannot figure out why the station keys and sends diagnostic messages but the controller reports a No Response alarm. The CPB board ships from the factory with a Group ID of 0 and should never be changed. For the Advanced Control, ASC 1000, and ASC 1500 product, the Group ID is not a changeable value and defaults to 0. The Group ID concept has been canceled in these new products. When upgrading system equipment be sure the paging transmitters have group ID's of 0 so that diagnostic messaging is possible with these new products.

The Individual Station ID is used to uniquely assigns an ID to each paging transmitter so that they can be communicated with individually by the controller. The Individual Station ID has 1024 values, ranging from 0 to 1023. The ID is set locally at the paging transmitter during installation. Care must be taken not to assign two stations with the same Individual Station ID since diagnostic messaging will not be possible for both transmitters. The Individual Station ID has no bearing on paging key-ups, only diagnostic or individual station testing key-ups.

The DRC 1 format has provisions for transmitter keying on up to 4 frequencies and 254 sectors, for both the analog and binary paging modes and transmitter test modes. The DRC 1 message format allows for the following paging transmitter diagnostic messaging, forward and reflected power readings, delay line setting, station audio gain and inversion, station frequency adjust, wild card input reads, and wild card output writes, and level 1 alarm information. Level 1 alarms are specific to the PURC 5000 paging transmitter alarm set and include, Tx fault, PA fault, synthesizer out of lock, low deviation, battery revert, system timer, external 1, and external 2 alarms. For Micor DRC stations all diagnostic messaging and alarms apply except for the station frequency adjust capability and PA fault alarm.

2.4 DRC 2
DRC 2 is the communications protocol used by the Advanced Simulcast Controller 1500 (ASC 1500) and base stations equipped with Advanced Control (JQB model transmitters or Micor stations retrofit with Advanced Control). Advanced Control paging transmitters are unique in the sense that they can decode both DRC 1 and DRC 2 messaging. This was done to make the base station compatible with any system currently in use. The station operating language, DRC 1 or DRC 2, is therefore dependent on the controller being used in the system.

To better understand DRC 1 communications for key control and diagnostic messaging the following two DRC parameters must be discussed, namely, the System ID, and the Individual Station ID. The System ID has 16 possible values, ranging from 0 to 15. The System ID uniquely associates a paging transmitter with an ASC 1500 DRC controller. The controller and paging transmitter must be programmed with matching System ID's if they are to communicate. Key control for paging is based on the System ID alone. As mentioned in the DRC 1 section, the Group ID parameter has been canceled for DRC 2 messaging. When converting a system from DDC or ASC 1000 controller operation to ASC 1500 controller, the system ID must be with in the 0 to 15 range. Use the original controller to change the station System ID to a value between 0 and 15.

The Individual Station ID is used to uniquely assign an ID to each paging transmitter so that they can be communicated with individually by the controller. The Individual Station ID has 1024 values, ranging from 0 to 1023. The ID is set locally at the paging transmitter during installation. Care must be taken not to assign two stations with the same Individual Station ID since diagnostic messaging will not be possible for both transmitters. The Individual Station ID has no bearing on paging key-ups, only diagnostic or individual station testing key-ups.

The DRC 2 format has provisions for transmitter keying on up to 4 frequencies and 254 sectors, for both the analog and binary paging modes and transmitter test modes. The DRC 2 message format can support all alarm and diagnostic information provided by DRC 1 messaging however it is communicated in a much more efficient manner. The DRC 2 format allows for new messaging required for Advanced Control and ASC 1500 systems which could never be implemented with the DRC 1 format.

2.5 KEY ON DATA
Key on Data is more a fixed operating configuration of the transmitter rather than a specialized control scheme. The transmitter, when equipped with the proper software and hardware, will key and transmit in the binary mode upon detection of paging data. Depending on the system application the internal station paging modem can be used or an external source of binary data can be used. This capability allows a Motorola transmitter to operate in a competitors binary only system. For this type of operation the customer will need an external alarm reporting system to monitor the transmitter if remote diagnostics is a concern. The station may or may not require external data delay compensation for the transmitter when operating in a simulcast system. This is largely dependent on the transmitter model, JLB or JQB, station hardware and software PURChased, and the information channel type, analog or digital. Key on data can also be used as a temporary control method for binary only systems when the customer is not in a situation to PURChase the proper infrastructure and is willing to forfeit remote transmitter diagnostics.

2.6 DIRECT DIGITAL CONTROL
Direct Digital Control refers primarily to the method of information transfer as opposed to the content of the information. Direct Digital Control is based on DRC messages however the messages are in digital form, a bit stream, as opposed to being in analog form, MDC modem tones of 1200 and 1800 Hz. With this mode of operation the paging data is also transferred to the base station in the digital form, as opposed to being converted to analog form, 1200 and 2200 Hz. modem tones.

Direct Digital Control is currently used for digital satellite distribution channels. The ASC 1500 and Advanced Control paging stations are required for this type of system operation. The ASC transmits MDC in digital form at 1200 baud and then passes or generates paging terminal data in the digital form as well. The ASC when used to pass terminal data, expects data from the terminal at RS 232 levels and outputs the data at RS 232 levels. Pass through digital transmissions are restricted to baud rates of 300, 600, and 1200. The ASC when used with an MPS 2000 terminal can be configured to generate the paging information. In this manner the ASC acts like the terminal output card. Paging data is user selectable for TTL or RS 232 output levels. The ASC also provides handshake signals, Request-To-Send (RTS) and CTS-To-Send (CTS), to be used for interface with the external Digital transmission equipment for the satellite uplink.

CONTROL AND PAGING INFORMATION CHANNEL

3.0 RF CONTROL
Control and paging information is transmitted from the terminal and controller site via wire line to a link transmitter. Key control for Motorola link transmitters is accomplished by sending High Level Guard Tone (HLGT), a 2175 Hz. audio tone. Once the link transmitter is keyed, activity on the channel will keep the link keyed. A loss of activity for a longer period than the station drop out delay (user set to 2,4, or 8 seconds) will cause the link transmitter to fall off the air. All base stations within acceptable signal strength range of the link transmitter require a link receiver to be installed in the station on the link transmitter transmit frequency. A single link transmitter will be able to support a limited geographic area of coverage depending on power output of the link transmitter and the terrain of the coverage are, flat or mountainous. Link Repeaters are used in conjunction with the link transmitter to extend the geographic coverage area of an RF control paging system.

A link repeater listens to the link transmitter with a receiver on the link transmitter frequency and rebroadcasts the audio (repeats the audio) on another frequency. All base stations within acceptable signal strength range of the link repeater require a link receiver to be installed in the station on the link repeater transmit frequency. Key control for the link repeater is accomplished with HLGT and activity similar to the link transmitter. A second link repeater could be added in a daisy chain fashion to extend system coverage again. Each successive link repeater requires an additional transmit frequency to avoid unwanted RF collision of information. All base stations within acceptable signal strength range of the second link repeater require a link receiver to be installed in the station on the second link repeater transmit frequency. See figure 5 below which graphically represents the link transmitter and link repeater system.

Figure 5

FIGURE 5. RF Link Transmitter and Link Repeater System Configuration

With this daisy chain link transmitter and link repeater configuration special system considerations must be made depending on the desired paging mode supported by the system. For a binary only system audio propagation delay is the crucial parameter for simulcast integrity. In this type of system the delay line settings for stations can be calculated by air mile distances from the link transmitters and repeaters. Stations which listen to link transmitter must be compensated by an additional 290 microseconds since each link repeater adds that much propagation delay to the stations it feeds relative to the originating audio signal. For a mixed system of analog and binary paging, an audio equalizer may be needed for the second link repeater to properly phase the audio for analog simulcast. This is dependent on the users level of desired quality of the signal in the overlap area of the first and second link repeater.

Motorola offers link transmitters and repeaters in Midband, VHF, UHF and 900 Mhz. bands. Link transmitters are also available in a hot standby configuration. This is recommended for RF control systems since the channel must be up at all times for paging service to be provided. Battery back-up configurations are also recommended if AC power failures are of concern at the site. Battery back-up operation provides limited service to counter AC power losses of several hours. To guard against co-channel users and intermodulation in high RF environments, Motorola link transmitters and repeaters can be operated with Private Line (PL) or Digital Private Line (DPL) signaling. PL and DPL are forms of coded squelch used by the receiver as a qualifier for un-squelching. This effectively adds password type security to receiver access as opposed to just RF carrier un-squelching a receiver.

As mentioned earlier link transmitters and link repeaters are keyed using HLGT. HLGT duration should be kept at a minimum to avoid wasting system air time, however it must be long enough to guarantee reliable system keying. The duration of HLGT required for the system is determined as follows. Each link transmitter and carrier squelch link repeater require 120 milliseconds of HLGT to key. Each link repeater with DPL squelch requires 300 milliseconds of HLGT to key. If the paging transmitters use DPL squelch receivers then add an additional 180 milliseconds of HLGT. System required HLGT duration equals the sum of HLGT for the link transmitter, plus any carrier squelch link repeaters, plus any DPL squelch link repeaters, plus 180 milliseconds if the paging transmitters have DPL link receivers.

3.1 WIRELINE DISTRIBUTION CHANNEL
In a wire line control paging system, controller output audio is fed into an audio splitter network and then distributed to each station via a Radio Land Line or Radio Tie Line. The phone line to the station is a dedicated 2 wire pair with voice and data quality comparable to a 3002 line or better. A wire line distribution network imposes additional concerns for a simulcast analog and binary paging system. Phone line specifications for audio gain, delay and various other parameters can vary substantially in the course of a day thereby affecting simulcast performance. Wire line outages are always a risk and out of the control of the system operator. Maintaining equalization of the system requires a greater effort as compared to an RF distribution medium which is much more stable to variations. Wire lines also impose a monthly cost per line to the operator which are subject to rate increases. An RF distribution system is always recommended over a wire line distribution channel, however local operator restrictions such as no available RF link frequencies or a phone company owned operator may dictate a wire line distribution system.

3.2 SATELLITE DISTRIBUTION CHANNEL
A Satellite distribution channel offers an alternative to conventional RF link and wire line systems. In areas where the RF link spectrum is fully allocated, satellite distribution offers relief. A satellite distribution channel is also attractive for wide area coverage since the satellite signal can span a large geographic area. Once the basic system is in place expansion merely involves adding sites. With an RF link or wire line system, expansion involves adding additional RF hops and increased dedicated wire lines with continuing increased distance and cost. The more complex the system the greater the effort to maintain the system and ensure simulcast integrity. Satellite distribution offers some attractive simplifications however satellite technology adds some new twists to the system.

Satellite transmissions are hampered by "sun outages" and rainfall. Sun outages predominantly occur around the Spring and Fall equinox for several week periods. The outages can typically last anywhere from 0 to 10 minutes or less and can be predicted. The phenomena occurs when the sun lines up with a geostationary satellite in a direct path with the receiving antenna dish. The signal is swamped out by receiver noise when this occurs and reliability is greatly reduced. Due to the predictability of the phenomena the paging operator can inhibit paging however customer service is greatly hampered. Rainfall, which can occur at anytime, also degrades satellite reception. The effect of rainfall degradation can be countered by increasing the satellite receiver signal strength with an increase in dish size. As can be expected and increase in dish size also implies an increase in cost.

Satellite service currently provided for use in paging transmitters is in the C-Band (4-6 GHz.) and Ku-Band (12-14 Ghz.). Both bands have their respective advantages and disadvantages. C-Band is less vulnerable to rainfall effect and up link service fees are less than Ku-Band, however terrestrial microwave interference is a greater risk and receiver equipment is costlier compared to Ku-Band.

Ku-Band receive equipment is less susceptible to terrestrial microwave interference and less expensive compared to C-Band. Ku-Band however is effected more by rainfall and up link service is costlier compared to C-Band. Satellite service providers offer a variety of modulation methods and service in both the analog and digital transmission modes. The current available analog transmission technologies are FM squared, Single Side Band Suppressed Carrier (SSBSC), and Single Channel Per Carrier (SCPC). The current available digital transmission technologies are FM squared, FM cubed, and Single Channel Per Carrier (SCPC). The proper technology is selected based on a variety of system factors including, level of desired reliability, geographic service area, paging formats supported by system, analog or digital transmission requirements, cost,equipment availability and multiple vendor sourcing, etc. . . Consult systems engineering for further information.

PAGING CONTROLLERS

Motorola offers several stand alone controllers for interface with a paging terminal for TRC and DRC control. The paging TRC protocol has been licensed to several large terminal manufacturers therefore a TRC controller is not needed in systems where the terminal can perform TRC encoding. For DRC systems the protocol is propriety and a controller is always needed.

4.0 PAGING STATION CONTROLLER (PSC)
The PSC is a stand alone TRC controller which supports link transmitter and repeater keying and single frequency paging transmitter keying for analog or binary paging. The PSC also support link transmitter keying on HLGT. The controller accepts terminal audio on separate 600 ohm voice, tone, and FSK modem screw terminal inputs with independent level adjust pots. PSC output audio is provided on a single 600 ohm screw terminal output. The controller supports paging terminal requests Key Analog (KA) and Key Binary (KB) as TTL inputs. The controller will grant Clear to Page Analog (CTPA) and Clear to Page Binary (CTPB) TTL outputs to the terminal when an input is successfully serviced. This communication handshaking of KA-CTPA and KB-CTPB allows the system to process paging requests in a controlled manner. Local front panel keying is possible as well as audio jack fields for testing and servicing. The unit has external 12V battery back-up, charging, and alert on loss of AC power capability. The unit also supports an inhibit signal used in shared channel applications by a paging terminal. The PSC is available in a single model, T3050A, and more detailed information can be found in Motorola manual publication 6881063E15.

4.1 SIMULCAST SYSTEM CONTROLLER
The SSC is an upgraded PSC which supports link transmitter and repeater keying and single frequency paging transmitter keying for analog or binary paging on up to 4 sectors. Sector control is accomplished by disabling stations individually prior to keying. With the SSC, paging stations can be configured in four independently-addressable sectors and any combination of stations (30 maximum) can be keying in one of four sectors. The SSC is offered in three different models with maximum capability to individually disable up to 30 transmitters. Model T3051A can individually disable up to 10 transmitters, model T3052A can individually disable up to 20 transmitters, and model T3053A can individually disable up to 30 transmitters. The SSC provides additional front panel switches, 10,20 or 30 depending on the model, for local individual station disabling control. For system testing purposes any group of transmitters can be keyed locally from the controller. Further detailed information regarding sector and individual station control can be found in Motorola manual publication 6881063E15.

4.2 DIGITAL DIAGNOSTIC CONTROLLER
The Digital Diagnostic Controller, DDC for short, was Motorola's first product offering for Digital Remote Control arena. The DRC system introduced base station diagnostic and alarm reporting concepts, remote station programming, and increased control capability for sector paging and individual station testing. The DDC provides automatic diagnostic polling and time stamped error logging. Database management is accomplished via a video display terminal and information is retained in non-volatile memory. Terminal and peripheral equipment interface is provided via a 50 pin punch block. The controller accepts terminal audio on separate 600 ohm voice, tone, and FSK modem inputs with independent level adjust controls. The DDC also has a built in 202T paging modem and can accept binary information in the digital data form instead of FSK audio from the terminal. DDC output audio is provided on a single 600 ohm audio output with an independent level adjust control. The controller supports paging terminal requests Key Analog (KA) and Key Binary (KB) as TTL inputs. The controller will grant Clear to Page Analog (CTPA) and Clear to Page Binary (CTPB) TTL outputs to the terminal when an input is successfully serviced. This communication handshaking of KA-CTPA and KB-CTPB allows the system to process paging requests in a controlled manner. The DDC also provides logic interface for terminal channel frequency and sector select control and relay contact closures for major and minor alarm indication. The DDC provides limited led display of operating status locally on the front panel as well as audio jack fields for testing and servicing.

The DDC DRC system supports link transmitter and repeater keying and up to four frequency paging transmitter keying on up to 256 sectors for analog and binary paging. The DDC can service 1024 individual DRC transmitters for testing purposes and individually key any group of up to four transmitters. The DDC uses DRC1 MDC 1200 messaging for communicating information to and from the transmitters. Diagnostic messaging requires an audio feedback path from the base stations to the controller. This feed back path can be either an RF return path or wire line return path. The RF return path requires a monitor receiver on the paging transmitter frequency to allow for base station generated messages to be recovered by the DDC. For systems requiring more than one receiver a SpectraTac Voting receiver configuration is required. This system mode of operation is often referred to as "Over the Air" diagnostics and messaging. If dedicated wire lines are available from each transmitter site then diagnostic messaging can be accomplished using an audio combiner to return the DRC audio to the DDC. The system operator chooses which feedback path is more appropriate for their system. The feedback path has no bearing on paging throughput. Diagnostic messaging is a background operation to be performed when no paging requests are present. Paging has priority and diagnostics will be interspersed with paging traffic when diagnostics are invoked. If the system is heavily loaded diagnostics may take hours to complete.

The DDC has one standard hardware model, N1450, and can be upgraded in software for added communications features and capabilities. The standard DDC comes with a 120VAC power supply, a Video Display Terminal, a 50 pin punch block and all required interconnecting cables. The unit can be rack mounted or left stand alone. Additional options are available including 230V AC power supply, Omit VDT, -48V DC power supply, and extended cable lengths (25 and 50 ft.) for long VDT and punch block runs. Peripheral equipment such as a printer and modems for remoting the VDT are also available. Motorola publication 68P81000B80, Digital Diagnostic Controller N1450 Users Guide and Installation Manual, should be consulted for further detailed information regarding operation and capabilities. Motorola publication 6881000B85, Digital Diagnostic Controller N1450, should be consulted for hardware servicing information.

4.3 ENHANCED DIGITAL DIAGNOSTIC CONTROLLER
The term enhanced refers to a firmware upgrade which adds additional station messaging as well as new DDC features. The enhanced DDC still uses the standard DRC1 MDC 1200 messaging format. The standard shipping DDC software is denoted on the VDT main screen as version 1.X. (The X refers to the release, 1.6 is the latest) The standard software has 8 main menus or operating screens that can be accessed. The enhanced DDC software is denoted on the VDT main screen as version 2.X. (The X refers to the release, 2.5 is the latest). The enhanced software has added 2 new screens in addition to the 8 original screens. Motorola manual publication 6881101B56, Digital Diagnostic Controller DDC Software Enhancement, should be consulted for detailed installation, configuration, capabilities and operation of these features.

Enhanced DDC New Features

Database Back-up: Two DDC's can be connected via a straight dB 25 cable using serial port 3 on the back of each unit. Configuration plug DTE3 on one of the units must be made opposite of the other. Once this is done then the contents of the memory from one DDC can be transferred to another unit or it can be retrieved from the other unit. This allows the system operator to configure a second standby DDC automatically, avoiding tedious key stroking and complete database reprogramming in the second unit. The feature can also be used to keep the standby unit current when changes are made to the main DCC database. This is a manually invoked process, therefore the standby unit will not automatically update when connected to a DDC whose database is modified.

Automatic Diagnostic Polling Changes: Diagnostic polling was intended to run as a background task so as not to interfere with paging throughput. On heavily loaded systems a situation can develop where diagnostics are unable to squeeze in between paging traffic to complete a full system poll. To combat this the user can force the polling cycle by giving it priority over paging. The terminal will not be granted a Clear to Page until polling is completed. The terminal must have sufficient batching capability, several minutes, so that it does not run out of memory and lose pages or crash when inhibited. The standard DDC can be programmed for automatic diagnostic polling on the hour and only 5 times during the day. The enhanced DDC firmware still supports 5 programming times however a mode can be selected whereby diagnostic polling is performed every single hour, 24 times a day. The enhanced firmware also supports a TTL input signal, EXTERNAL POLLING TRIGGER, to let the user invoke a full system diagnostic poll at any time, and provides an external TTL POLLING IN PROGRESS output signal. This feature is activated by hardware jumper, JU17 (B position). This feature, when used, will replace the standard punch block signals ABORT (becomes EXTERNAL POLLING TRIGGER) and CHANNEL LOCKOUT (becomes POLLING IN PROGRESS).

HLGT duration was increased and unnecessary transmissions of HLGT were eliminated: HLGT is used to key up link transmitters and repeaters in an RF link distribution system. The standard DDC provided a jumperable maximum HLGT duration of 900 milliseconds. It was found that some large RF link systems with multiple hops required HLGT durations in excess of 900 milliseconds. The enhanced software in conjunction with a hardware jumper change extended the maximum HLGT duration to 3.3 seconds. The standard DDC firmware also resent HLGT between DRC messages when it really wasn't necessary. To increase efficiency HLGT is now stripped from back to back DRC messages since the audio activity keeps the link keyed and the controller need not resend HLGT if the link is keyed. These changes to HLGT operation were also made to the standard DDC firmware,version 1.5F or greater.

DDC control of paging transmitter simulcast parameters, alarms and wildcard outputs: The enhanced DDC firmware can remotely read and write the digital delay line setting (0-2555 microseconds in 5 microsecond steps), the station analog audio gain (-6.4 to +6.2 dB in .2 dB steps), the audio inversion status, the carrier frequency offset, the forward and reflected alarm threshold settings, and the status of the four external wildcards. For full utilization of this feature, the base stations must be equipped with digital delay lines, digital wattmeters, remote frequency adjust hardware, wildcards, and enhanced base station software to decode and encode these additional DRC 1 MDC 1200 messages. Functionality of this feature will be determined by the amount of base station options present. This feature is a convenience type feature which allows the system operator to make programming changes without the need for a site visit. This feature also aids in simulcast optimization since the system operator can vary individual station simulcast settings while field personnel observe the performance of the system in the critical overlap areas.

4.4 ADVANCED SIMULCAST CONTROLLER 1000 (ASC 1000)
The ASC 1000 is a Motorola designed DRC controller intended to replace the Digital Diagnostic Controller, standard and enhanced. The ASC 1000 is a modular designed product available in a desktop stand alone configuration or a 19 inch rack mount configuration. The basic hardware is comprised of a power supply card, memory card and an Advanced Transmitter Controller (ATC) card. The 19 inch rack mount unit offers a manual switched back-up configuration with database redundancy. Controller programming and system monitoring is performed via any dumb VDT. Additional peripheral equipment includes a printer for hard copy output and a serial floppy drive for data base back-up. The ASC 1000 is available with 110V, or 220V 50/60Hz AC power input or -48V DC input. The controller interfaces to the outside word via a 50 pin punch block. The ASC 1000 communicates using DRC 1 messaging only.

For DDC replacement applications the following two points should be noted. The ASC punch block is not pin for pin compatible with the DDC 50 pin punch block for signal pin outs. The user will be required to punch down a new punch block for proper signal connection to the ASC from the existing system. When an ASC is used to replace a DDC a new punch block must be wired into the existing system. There is one feature that the ASC 1000 does not support that is available with the Enhanced DDC. The feature is an external diagnostic polling trigger (DDC ABORT signal) and a polling in progress handshake (DDC CHANNEL LOCKOUT signal). See the Enhanced DDC section "Automatic Diagnostic Polling Changes" for more detailed feature explanation.

The ASC 1000 also brings new features and capabilities not available with the standard or enhanced DDC. The ASC 1000 supports the following new features:

4.5 ADVANCED SIMULCAST CONTROLLER 1500 (ASC 1500)
The ASC 1500 refers to a software upgrade that adds a multitude of new features and capabilities above and beyond the ASC 1000. The ASC 1000 and 1500 share the same hardware platform and 50 pin punch block interface to the outside world therefore no special rewiring is required when an ASC 1000 is upgraded to an ASC 1500. Some hardware/software incompatibilities may exist for early production ASC 1000's memory and ATC cards when trying to upgrade to an ASC 1500. The details of any hardware and software incompatibilities can be found in the separate detailed ASC documents.

The ASC 1500 is intended for use in systems which desire to fully utilize all the capabilities of the Advanced Control base station. Unlike the ASC 1000 which communicates using DRC 1 messaging only, the ASC 1500 communicates using DRC 2 messaging exclusively. DRC 2 messaging was invented to allow for additional messaging and communication as well as future expansion between the Advanced Control Base station and the ASC 1500. Due to the exclusive DRC 2 messaging used by the ASC 1500 it is required that the base station infrastructure be of the Advanced Control type. The ASC 1500 provides basic paging system operation with the following additional capabilities. Usage of some of the addition system features may require additional peripheral hardware such as modems,printers, etc.

New Features

Unsolicited Alarm Reporting: The ASC will report alarm information sent by an Advanced Control base station even though the ASC was not requesting alarm information from the station. Alarm information is forwarded to the ASC by dedicated return wire lines or dial-up phone lines. This is a real time alarm reporting method. Dedicated wire lines provide the fastest message response time. In a dedicated return wire line system message collisions between competing stations can occur. To counter the effects of data collisions the base station randomly keeps sending the alarm message until the ASC acknowledges the base station with a receipt confirmation. The ASC acknowledges the base station via the outbound control channel. Paging is temporarily inhibited while the ASC acknowledges the station. For a wire line return path, a phone line audio combiner is required to sum all the station wire lines to one input audio port on the ASC. For a dial-up phone line return path system a modem and dial-up phone line is required at each base station and one at the ASC. A Dial-up phone line return path system will add a small delay due to modem dialing and connect time when reporting an alarm. Alarm message collisions from multiple stations are not an issue since the phone system will busy out stations when the ASC is currently servicing an alarm from another station. Busied out stations continue to retry until a connection with the ASC is established. When a station gets through to the ASC it is acknowledged immediately via the modem connection so no inhibit of the paging system is required. An occasional full system diagnostic poll via modems would be required to determine if any of the dial-up phone lines are inoperative or a station is completely dead.

Dial In Dial Out Diagnostics: Traditional diagnostic polling requires the paging channel to be inhibited while diagnostic messaging is in progress. This can become a problem for heavily loaded systems which are at maximum user capacity, throughput is already poor and the channel is continuously in use not allowing diagnostics to ever complete. Dial In Dial Out Diagnostics is a method for allowing diagnostic polling without interrupting paging service. The feature requires the ASC to be equipped with a modem and dial-up phone line as well as each station having a modem and dial-up phone line. When polling is initiated by the ASC it will attempt to dial each station and interrogate the station for any alarms. The process runs in parallel with paging activity and does not inhibit use of the paging channel.

Automatic Delay Equalization: This feature allows the ASC to automatically measure relative individual base station audio propagation delays for the outbound control path which feeds each station. Once all the data is acquired and evaluated, the ASC will automatically compensate individual station digital delay lines such the system is operating optimally for simulcast binary paging. For the feature to be operational, the system must have a SpectraTac monitor receiver infrastructure in place and all transmitters must be able to communicate back with the ASC through the SpectraTac system. The base stations must all be of the Advanced Control type. For binary paging, audio delay compensation is the parameter of importance for simulcast integrity. This feature will not compensate for critical analog voice paging parameters such as audio gain, and transmitter carrier frequency drift. This feature is an automatic equalization system for binary paging only. Analog paging supported on the system will still have to be attended to via manual testing and compensated for manually. From the ASC, the station audio gain and carrier frequency can be adjusted by editing and writing the station parameter settings for audio gain and carrier frequency. (See the Auto Equalization document, not yet published, for detailed system requirements, installation and alignment information)

Remote Logging Printer: The ASC supports logging system and station alarm information to a remote printer. This allows the user the capability to monitor system activity from several operations across the country from a central location. The feature requires two external modems, one at the ASC and one at the printer location, a dial-up phone line, and a printer. The ASC will dial out and connect to the printer when ever new system or station alarm information is received and provide a time stamped hard copy of the alarms. The ASC error log information is maintained locally internal to the ASC database for local inspection as well.

Direct Digital Interface: For RF link and wire line control information distribution systems, the ASC output is in an analog format composed of DRC MDC modem tones, FSK paging modem tones, signaling tones, and voice. For a digital satellite channel analog information cannot be transmitted and the information to be transmitted must be in the digital format. For this type of specialized system, binary only paging can be supported since tone and voice transmissions cannot pass through the digital satellite channel. The DRC MDC modem tones and FSK paging modem tones originate as digital information in the ASC and are converted to analog signals for transmission in RF link and wire line systems. For the digital satellite distribution channel the ASC base band digital information is fed directly to a satellite up link and transmitted to each base station. The base station receives the digital bit stream from a satellite receiver and processes control and paging information accordingly. Diagnostics for this type of system are still possible but require an analog return path, return wire lines or a SpectraTac monitor receiver voting comparator system, from the transmitter network. Diagnostic messages are sent to the transmitters in the digital format and base stations responses are received by the ASC in the analog format.

N+1 Redundancy: As mentioned earlier an ASC 1500 is comprised of a power supply card, a memory card, and an Advanced Transmitter Control card, ATC for short. One ATC card is required to control a single channel of transmitters. The ASC card cage can support up to five ATC cards, therefore 5 separate channels can be controlled from a single ASC card cage when five ATC cards are present. N+1 redundancy refers to a special wire line control system configuration whereby up to 4 channels, all in the same frequency band of operation, VHF, UHF, or 900 Mhz, can be backed up by one transmitter as a hot standby in the event a transmitter failure occurs on one of the channels. This type of system implies that each transmitter site has one transmitter from each channel present. In addition each of the site transmitters is connected to a Motorola designed N+1 redundancy panel which contains wire line and antenna switching circuitry controlled by the standby transmitter. The standby transmitter can then fill in for a transmitter on a channel that it recognizes has a problem. The standby transmitter, also referred to as the master station, communicates with all the other stations, referred to as slaves, via a station Local Area Network, LAN for short. The master station continuously polls all the slave transmitters via the LAN to determine if a problem exists, and switches in for a station when a failure is detected. N+1 redundancy therefore refers to the ASC 1500's ability to manage and maintain such a complex system of up to four channels with a single backup transmitter. The feature is primarily used in international markets where governmental agencies are the primary paging service providers. These types of systems have not yet been introduced into domestic U.S. markets.

Forward Power Readings Saved in Ram: The ASC 1500, which uses DRC 2 messaging, has the capability to acquire station forward and reflected power readings during diagnostic polling in addition to station alarm information. The DRC 1 format had limited messaging capabilities, hence the creation of the DRC 2 format to allow for such improvements in station communications. The ASC will save a history file for each individual transmitter that is polled. The file contains the status of the station power readings and alarm information for the last three diagnostic polls performed. The history file will overwrite the oldest logged entry with a new entry as polling continues.

LINK TRANSMITTERS

5.0 MICOR PURC
Motorola link transmitters are wire line control continuous duty FM transmitters. The transmitters have flat audio response and link keying is accomplished using HLGT. Once keyed, the link will remain keyed until audio activity has ceased. Upon loss of activity the transmitters will drop off the air. The drop out delay is adjustable and user set to 2,4, or 8 seconds. The transmitters are capable of generating Digital Private Line signaling to reduce problems due to co-channel users in the same geographic area. Digital Private Line, DPL for short, is a low speed sub-audible signal which represents a 23 bit binary word. DPL is used by a receiver as a qualifier for un-squelching. Not only must the receiver sense the carrier frequency but the DPL code must be continuously decoded for the receiver to pass audio. Motorola booklet 6881106E83 can be ordered for further detailed information regarding DPL.

Antenna connections to the link transmitters are of the UHF female type for all links except the 125 Watt Midband link. The 125 watt Midband Link is a hybrid station comprised of Micor control and low level RF circuitry with PURC 5000 power supplies and PA decks. The link transmitters are offered in a hot standby redundancy configuration in the event a failure occurs in the main station. Without a back-up unit a failure to the link transmitter would render the system useless until the link is repaired. It is strongly advised that systems be engineered employing hot standby configurations for link transmitters. Link transmitters are also available with battery back-up/charging operation in the event an AC power outage occurs at the site. The stations are also available with alternate AC power supplies for use in international markets. For servicing it is advised the links be ordered with a wattmeter and power and modulation alarm indication.

5.1 PURC 5000
Link transmitters in the PURC 5000 family of stations are only available in the 928-960 Mhz. band. The link transmitter is an FM continuous duty transmitter with variable power out from 50-150 watts. The link transmitter has a flat audio response and link keying is accomplished using HLGT. Once keyed, the link will remain keyed until audio activity has ceased. Upon loss of activity the transmitters will drop off the air. The drop out delay is adjustable and user set to 2, 4, or 8 seconds. The transmitters are capable of generating Digital Private Line signaling to reduce problems due to co-channel users in the same geographic area. The links are available for standard 25 Khz channel spaced systems as well as for newly opened 12.5 Khz. channel spaced systems in the 928-960 Mhz band. The link transmitters are available in a hot standby configuration for redundancy operation. Link transmitters are also available with battery back-up/charging operation in the event an AC power outage occurs at the site. The stations are also available with alternate AC power supplies for use in international markets. For servicing it is advised the links be ordered with a digital wattmeter.

LINK REPEATERS

6.0 MICOR LINK REPEATERS
The link repeater is a link transmitter with a link receiver added to it. Link repeaters are not restricted to a particular frequency band for operation, the transmit and receive frequencies can be from different bands. Midband, UHF, or 928-960 Mhz. link receivers can be used to make a link repeater. Link Repeaters have a flat audio response and ink repeater keying is accomplished using HLGT. Once keyed, the repeater will remain keyed until audio activity has ceased. Upon loss of activity the repeaters will drop off the air. The drop out delay is adjustable and can be set to 2,4, or 8 seconds. The transmitters are capable of generating Digital Private Line signaling to reduce problems due to co-channel users in the same geographic area. Link repeaters are offered in a hot standby redundancy configuration in the event a failure occurs in the main repeater. Without a back-up unit a failure to the link repeater would render the stations which listen to the link repeater useless until the repeater is repaired. It is strongly advised that systems be engineered employing hot standby configurations for link repeaters. Link repeaters are also available with battery back-up/charging operation in the event an AC power outage occurs at the site. The stations are also available with alternate AC power supplies for use in international markets. For servicing it is advised the link repeaters be ordered with a wattmeter and power and modulation alarm indication.

6.1 PURC 5000 LINK REPEATERS
Link repeaters in the PURC 5000 family of stations are only available in the 928-960 Mhz. band. The link repeater is a continuous duty FM transmitter with variable power out from 50-150 watts.

The link repeater is a link transmitter with a link receiver added to it. Link repeaters are not restricted to a particular frequency band for operation, the transmit and receive frequencies can be from different bands. Midband, UHF, or 928-960 Mhz. link receivers can be used to make a link repeater. For link receivers in the 928-960 Mhz. band both 25 Khz or 12.5 Khz channel spaced receivers are available. The Link Repeater has a flat audio response and keying is accomplished using HLGT. Once keyed, the link repeater will remain keyed until audio activity has ceased. Upon loss of activity the repeaters will drop off the air. The drop out delay is adjustable and user set to 2, 4, or 8 seconds. The repeaters are capable of generating Digital Private Line signaling to reduce problems due to co-channel users in the same geographic area. Link repeaters are offered in a hot standby redundancy configuration in the event a failure occurs in the main repeater. Without a back-up unit a failure to the link repeater would render the stations which listen to the link repeater useless until the repeater is repaired. It is strongly advised that systems be engineered employing hot standby configurations for link repeaters. Link repeaters are also available with battery back-up/charging operation in the event an AC power outage occurs at the site. The stations are also available with alternate AC power supplies for use in international markets. For servicing it is advised the link repeaters be ordered with a digital wattmeter.

PAGING BASE STATIONS

7.0 MICOR TRC
Micor paging base stations are single frequency, continuous duty, variable power output FM transmitters. They accommodate two tone, 5/6 tone, voice, and binary FSK-NRZ signaling for tone alert, tone and voice, numeric display, and alphanumeric display paging. They were available in Low Band, VHF, UHF and 900 Mhz bands. Low Band models range in power out from 50-100 and 150-350 Watts. VHF models range in power out from 50-100 and 50-350 Watts. UHF models range in power out from 30-60, 30-75, 100-225, and 100-250 Watts. 900 Mhz models range in power out from 25-300 Watts. The transmitters were available in both simulcast and non-simulcast models.

The low power transmitters are fully solid state. The high power transmitters are fully solid state except for the power amplifiers which still use a tubes for the finals. Transmit and receive frequencies are crystal controlled and not synthesized across the band of interest. Transmit and receive frequency changes require channel element changes and retuning. The stations are available in both wire line and link receiver control.

The Micor family of paging transmitters are available in both indoor and outdoor cabinets and require both rear and front door access for installation and servicing. The internal component assemblies typically have a gray or silver finish. The stations are typically referred to as one of two type, either UNIFIED or NON-UNIFIED, describing the control chassis mechanics. The unified control chassis houses control, receiver and transmit exciter circuitry. The non-unified control chassis houses only the control circuitry, the receiver and transmitter exciter are separate components. The control chassis is a modular design with various control cards which are interconnected by a connectorized back plane. Two separate back planes exist, one for the unified chassis and one for the non-unified chassis. All connections to the back plane are made by either screw terminal, bubble pins or specialized connectors. The control cards are the same for both unified and non-unified stations. The stations are fully factory assembled and tested for analog and binary operation. The delay line option if ordered is a drop ship item and installed in the field on installation. The delay line is an passive delay line manufactured by Allen Avionics and ranges in delay from 0-1100 microseconds, adjustable in 5 microsecond steps. The paging modem is also a drop shipped item which is installed in the field during station installation. The modem converts incoming FSK audio paging tones into RS-232 level digital signals which are then used to modulate the transmitter as FSK-NRZ data.

The paging modem used is a Bell 202 type modem which uses 1200 & 2200 Hz. modem tones. The recommended modem is manufactured by Universal Data Systems, a Motorola owned subsidiary. The original manufactured modem has since been redesigned to new model which can only be identified by a size comparison. The new modem is smaller in size as compared to the original old modem. In addition to being smaller in size the new modem is much faster in passing data as compared to the old modem. In the event an old modem is replaced it with one of the new small modems it will have to be slowed down by using a QRN4612 modem delay module. This is required for simulcast compatibility.

Micor stations are available in both simulcast and non-simulcast models. For non simulcast models the paging synthesizer and delay lines will not be required. The stations are designed for receiver flat audio, the transmit audio can be either flat or pre-emphasized. Early analog paging systems used pre-emphasis in the stations for voice paging, however this function was moved to the paging terminal and the base station transmit audio path is predominantly ordered with flat transmit audio. For simulcast systems it is much better to pre-emphasize the audio once at the source than have all stations pre-emphasizing the audio independently.

The Micor PURC paging stations come standard with Paging Universal Remote Control (PURC), a Tone Remote Control format for transmitter keying in the analog and binary mode. Depending on the type of station ordered, simulcast or non-simulcast, the paging synthesizers and delay lines will be optional. Power supplies and PA decks will vary depending on the frequency band, power out, and desired AC line voltage option. Figure 5 below illustrates the general structure of a Micor PURC paging station for a Unified and Non-Unified chassis.

Figure 6

FIGURE 6. Micor Unified and Non-Unified Transmitter Block Diagrams

7.1 MICOR DRC
Micor DRC refers to a redesign of the Micor control section so that the station is compatible with Digital Remote Control. The redesign utilizes PURC 5000 technology as the core architecture for the control section. The conversion requires the original back plane and all existing control cards to be removed and discarded. A new back plane, unified or non-unified, is installed in place of the old one. Screw terminal, bubble pin, and specialized connector interfaces are preserved for ease of connection to the existing station components. The control chassis is self contained on a slide assembly and is installed into the left hand side of the control chassis divider. Service to the chassis is accomplished by sliding out the tray and flipping the tray open.

The new integrated control chassis replaces several existing station components as well as adding new features never before possible with Micor stations. The control tray has a built in Bell 202T paging modem which comes standard with the tray. An optional digital wattmeter and delay line can be ordered for full station capabilities. The DRC option with digital delay line will replace the existing UDS 202T modem and passive Allen Avionics delay line. The digital delay line has over twice the range, 2555 microseconds versus 1100 microseconds, of the Allen Avionics delay line. The DRC option requires the station to have transmit flat audio for proper operation. Stations without transmit flat audio must be upgraded prior to installing the DRC option.

The Micor DRC option uses DRC 1 messaging. The new control option allows for positive control, increased sector paging, individual station testing, and station diagnostics for alarms and forward and reflected power readings (when equipped with a digital wattmeter). The option also is compatible with Motorola dial-up diagnostics which run off of an IBM PC or compatible when equipped with a Hayes 212 modem or equivalent. The station can be controlled by either a DDC or ASC 1000. The DRC option has a software upgrade allowing it to have the wattmeter delay line board parameters remotely controlled manually. The software upgrade works with an Enhanced DDC or an ASC1000. The Micor DRC option is available as a field retrofit kit for both Unified and Non-Unified stations or can be factory installed.

The DRC option is not compatible with monitor receiver, time out timer, and voice actuated response (VAR) as supported with Micor PURC stations. The option is compatible with Low Band, VHF, and UHF stations, both high and low power. The option is not compatible with 900 Mhz. Micor stations due to a mechanical incompatibility with the 900 Mhz PA deck and the control tray folding out for alignment. Electrically the DRC option will work in a 900 Mhz. Micor station however installation, alignment and servicing will be a bit inconvenient The product was never intended to operate with 900 Mhz. stations since PURC 5000 900 Mhz. stations are simulcast compatible with Micor and the Micor 900 Mhz station was intended to be canceled. Figure 6 below illustrates the option as installed in a Micor station.

Figure 7

FIGURE 7. Micor DRC as Installed in a Unified and Non-Unified Station

The Micor DRC option is made up of 4 primary PC boards, in addition to the two back plane boards, one for unified and one for non-unified stations. The DRC control module is actually made up of two boards, a Control Processor Board (CPB) which handles all the logic interface to the rest of the control tray, and a Modem board which processes incoming DRC audio as well as generating DRC audio for diagnostics. The Micor Paging Control Board (MPC) performs transmit audio processing and supervises overall control tray operation and interface with the station. The digital wattmeter and delay line board function is self explanatory.

7.2 MICOR ADVANCED CONTROL
Motorola's next generation of Digital Remote Control is referred to as Advanced Control. The Advanced Control tray is a self contained stand alone 19" rack mounted assembly which performs all the DRC functions provided by the Micor DRC option in addition to adding further system features and capabilities. The Advanced Control tray is compatible with single transmit frequency Micor VHF and UHF Simulcast stations. Non-Simulcast stations are incompatible with Advanced Control option. The tray has a built in Bell 202T paging modem as well as a digital line (if ordered) so the Micor UDS modem and Allen Avionics delay line are not needed. The tray can handle DRC 1 or DRC 2 messaging therefore it will operate with any Motorola Digital Remote Controller.

The Advanced Control Option for Micor station is offered as a field retrofit kit only. The tray is interfaced to the Micor station using the Micor DRC back plane, Unified or Non-Unified, depending on the station type. The tray is mounted towards the bottom of the station. The space evacuated buy the UDS modem and Allen Avionics delay line is utilized to provide room for the Advanced Control Tray. The Paging synthesizer is relocated to the space where the modem and delay line were and the Advanced Control Tray is mounted in the location where the paging synthesizer originally was. See the Advanced Control Retrofit for Micor PURC Paging Stations manual, part number 6881127E15 for detailed application information.

Figure 8

FIGURE 8. Advanced Control Tray Hardware Block Diagram

The Advanced Control Tray is microprocessor controlled and uses Digital Signal Processing, DSP, for audio processing. The tray is a 19" rack mount stand alone tray. The control tray is made up of 4 printed circuit boards, the Advanced Control Board (ACB), the Power Supply Line Interface Board (PSLIB), the Display Board, and the Back plane board. The back plane board is fastened to the tray and the ACB and PSLIB board plug into the back plane. The back plane board provides connectorized interface for the tray modules as well as interface to the rest of the station hardware. The display board physically snaps into the front panel and plugs into the ACB board via a ribbon cable. The display board is made up of an 8 character alphanumeric display, 8 status and indicator LEDs, and a 16 function key pad for locally operating, programming, and aligning the station. The front panel flips open for servicing of the ACB and PSLIB board.

The ACB board performs control audio processing, synthesizer programming, transmit audio processing, and station and system level alarm recognition and reporting. The board contains no user adjustable potentiometers and board status, configuration, and alignment is accomplished via the display board display and keypad. The PSLIB board generates +5 volts for use by the logic circuits, from station supplied +13.8 and +9.6 volt supplies. Filtered +13.8 and +9.6 is passed through the PSLIB board to the ACB board for use by the audio processing circuits. The PSLIB board also contains phone line interface circuitry for wire line control stations. The tray is also available with an internal dial up/dial out modem with battery back-up and charging for diagnostic messaging. If ordered the modem is piggy backed on the PSLIB board. The batteries mount to the control tray cover above the PSLIB board. The tray comes with a wiring harness for interface to the rest of the station and the outside world.

7.3 PURC 5000 STATIONS
The PURC 5000 Paging Base Station is Motorola's line of paging transmitters to replace the Micor family of paging transmitters. PURC 5000 paging base stations are fully solid state multi frequency synthesized, continuous duty, variable power output FM transmitters. They accommodate two tone, 5/6 tone, voice, and binary FSK-NRZ signaling for tone alert, tone and voice, numeric display, and alphanumeric display paging. They are available in VHF, UHF and 900 Mhz bands. VHF stations are available in 125W and 350W models. UHF stations are available in 6, 40, 75, 110, and 225 watt models. 900 Mhz stations are available in 75, 150 and 300 watt models. The transmitters were available in both simulcast and non-simulcast models. The stations are available in both wire line and link receiver control.

The PURC 5000 family of paging transmitters are available in both indoor and outdoor cabinets. The station hardware and cabinet design have been reduced in size compared to the Micor transmitters. Station installation and servicing only requires single side access from the front of the station. All antenna, power, and control connections are made at the side of the station via the station J-box. This type of design allows the stations to fit flush against a wall or mount back to back in congested sites. The stations can also be stacked one on top the other. The 300 watt 900 Mhz station is the only exception, due to the PA and power supply requirements. The 300 watt 900 Mhz. station comes in either an indoor or outdoor cabinet and requires both front and rear access. All internal component assemblies either slide out on rails or fold out for servicing. The internal component assemblies are painted with a black finish.

Non-Simulcast PURC 5000 stations come standard with, Tone Remote Control, wire line control, a built in Bell 202 paging modem, minimum size required indoor cabinet, 120 V 60 Hz. AC power supplies, cooling fans depending on the make and model, RF tray and control as shown minus the wattmeter/delay line, and one or two PA decks depending on the power out, and a Low Pass Filter. Simulcast PURC 5000 stations come standard with all the Non-Simulcast station feature in addition to adding a Paging Synthesizer for increased TX frequency stability. Additional ordered options include a link receiver for RF control, digital wattmeter option for power out monitoring, digital delay line for simulcast equalization, second expansion tray for special applications using wild cards or RS232 communications, double and triple circulators, international power supplies capabilities, battery back-up options for stations, alternate cabinets, outdoor models or dual access Micor type cabinets, and Digital Remote Control. See figure 9 below for a visual representation of the PURC 5000 station.

PURC 5000 STATION BLOCK DIAGRAM

Figure 9

FIGURE 9. PURC 5000 Paging Transmitter Block Diagram

7.4 PURC 5000 CONTROL TRAY
The PURC 5000 control tray is made up of 6 primary printed circuit boards. The station control board is a microprocessor based board responsible for interfacing with the rest of the station. The station control board contains a code plug which contains the station transmit frequency information, antenna relay control information, time out timer information, and auto station identifier information. Any modifications the these parameters require a new programmed code plug available from an authorized Motorola service center. The Control board, TRC or DRC, and the PURC Board communicate with the station by a 64 bit matrix called a muxbus. The control tray boards can read and write to specific muxbus bits thereby communicating information amongst themselves.

Figure 10

FIGURE 10. PURC 5000 Control Tray Hardware Block Diagram

The control board slot can be occupied by either a TRC board or a DRC board pair. These control boards are microprocessor based and process both logic and audio information . The control boards continuously monitor incoming audio to the tray for control messages. The control boards do not process transmit audio. They exclusively perform control audio demodulation and via the muxbus tell the Station Control and PURC board what mode of operation to be in. TRC control provides no station transmitted diagnostic information, but DRC control does. DRC control allows for diagnostic messaging over the air or via the station line 2 wire line. The control boards contain line 1 interface and line 2 driver circuitry for phone line interface. See figure 10 below for an exploded view of the control tray.

First Expansion Tray
The first expansion tray contains a power supply board which buffers +13.8 and +9.6V from the station power supply and also DC-DC converts +13.8 volts to +5 volts for the PURC and wattmeter delay line boards microprocessor and logic circuitry. The first expansion tray snaps onto the control tray. The composite control tray rests on top of the RF tray which slides out for service. Service to the Control and Station Control boards is accomplished by flipping the tray to the right. The tray is hinged and will rest in the 90 degree vertical position with respect to the RF tray. The Control and Station Control board operate in the station in an up side down position. The first expansion tray boards are serviced by sliding out the RF tray and flipping up the first expansion tray lid. The first expansion tray has it own hinged lid.

The PURC board is a microprocessor based board responsible for processing analog and binary paging information. The PURC board monitors incoming station audio and will process analog voice or tone pages, or convert FSK modem tones to logic levels for binary paging. The PURC board controls the analog deviation, nominal and maximum, as well as providing binary deviation alignment for non-simulcast stations. The PURC board also has responsibility for supervising the wattmeter delay line board operation. The PURC board contains wattmeter look up tables for the various frequency bands. The look up tables are stored in program prom, therefore the code will vary from board to board, depending on the station frequency band and type of wattmeter element used in the station. The board firmware has several SP's available for the various bands to operate in a Key on Data mode for binary only systems. The board can also be jumpered to pass TTL or RS232 external paging data for applications where the internal paging modem is not needed.

The wattmeter delay line board is equipped with a three digit seven segment display to provide the user with visual information regarding station forward power output, reflected power and a calculated VSWR, when the station is equipped with a wattmeter element. The wattmeter option also allows the user to set alarm trip points when the forward power falls below the forward alarm set point or the reflected power rises above the reflected alarm set point. The display is also used to show numerically the station settings for the digital delay line. The digital delay line has a maximum delay of 2555 microseconds in 5 microsecond increments. The clock circuitry can be jumpered from 100 Khz. to 200 Khz. thereby changing the resolution to 10 microsecond steps and the total board delay is then doubled to 5110 microseconds. The change in clock rate degrades the delay line audio performance and should not be used for voice paging applications. The degradation can be tolerated by binary only paging systems running Golay or 512 POCSAG paging, usage with 1200 baud POCSAG is not recommended. The wattmeter digital delay line board contains audio gain and attenuation circuitry ranging from -6.4 dB to +6.2 dB in .2 dB steps. This board capability is only used for DRC stations equipped with remote gain and delay adjust.

Second Expansion Tray
The second expansion tray is only added to a station when wildcard capabilities are needed or remote dial-up diagnostics communications with the station is desired. A wildcard board is a logic board which has the capability to read 1-4 bits from the muxbus or write 1-4 bits to the muxbus. Typically a read operation is used to provide a control signal to the outside world that a station event has occurred and a write operation lets the outside world communicate an external event to the station. The wildcard inputs from the external world interface via opto couplers and the output wild cards can be open collector transistors or relay closures. The wildcard module is used as a tool by the product group to fulfill special customer needs in interfacing with the outside world. Special software may be needed in some cases to read and write and redefine the meaning of the muxbus bits. An example of using wildcards is for hot standby station operation. When a station is used to back-up another station the wildcard modules with specialized software are used to communicate operating and alarm status between the transmitters.

For PURC 5000 stations there exists an IBM PC based program which will display the station muxbus and allow the user to read forward and reflected power from a station equipped with a digital wattmeter. The feature requires the station to have a second expansion tray which houses a wildcard module and an RS 232 interface module. The station must also be equipped with an external auto answer Hayes compatible modem that runs at 300 or 1200 baud and must be connected to a dial-up phone line. The PC must also be connected to a Hayes compatible modem that runs at 300 or 1200 baud and be connected to a dial-up phone line. With this hardware in place the user can dial up a station and monitor transmitter muxbus bus information in real time. The various keying modes can be deduced from the muxbus bit status. Power readings will be displayed numerically and a VSWR calculation will be made when power readings are requested.

7.5 PURC 5000 TRC
The PURC 5000 TRC station is available in both Non-Simulcast and Simulcast models. For Non-Simulcast models up to 8 transmit frequency control is possible using the Non-Simulcast Function Tone set. For Simulcast stations up to 3 transmit frequency control is possible using the Simulcast Function Tone set. Simulcast stations can be controlled for sector paging and individual keying when used in conjunction with an SSC or paging terminal that can generate PURC control audio. TRC is the standard station control offering unless the DRC option is added. TRC controlled stations provide no direct remote diagnostic capabilities in the TRC system. A TRC station can support IBM PC dial-up diagnostics when properly equipped with a second expansion tray, wildcard module, RS 232 module and a Hayes compatible modem with a dial-up modem.

7.6 PURC 5000 DRC
The DRC option for PURC 5000 stations entails replacing the TRC control board with the DRC control board pair made up of a CPB board piggybacked on a DRC modem board. The PURC 5000 DRC option communicates using the DRC 1 message format. The DRC option brings with it more reliable control as well as remote station diagnostic capabilities for alarms and manual diagnostic testing for alarms and power readings. Diagnostics are remotely retrieved via an over the air return path or dedicated return wire lines from each station. The over the air diagnostics method requires a SpectraTac monitor receiver set-up and voting comparator if more than one receiver is required to listen to all the transmitters. The DRC option supports a total of 1024 stations per system, sector paging across 254 sectors, and 4 transmit frequency control. The standard DRC option supports 8 station alarms, Tx fault, PA fault, synthesizer out of lock, low deviation, battery revert, system timer, external 1, and external 2 alarms. Manual interrogation of the station will allow for forward and reflected power readings and a local controller calculated VSWR. The station must be equipped with a digital wattmeter for power reading capability.

For additional station communication features a software upgrade is available, commonly referred to as "Enhanced DRC" software which allows the user to modify the wattmeter delay line board settings remotely. The upgrade option is typically referred to as the "Remote Delay, Gain and Frequency Adjust" option. The software upgrade is made to the DRC CPB board and the PURC Board. New proms are required as well as adding an EEPROM to the PURC board so wattmeter delay line board settings are preserved in non-volatile memory. The upgrade also requires the DDC controller to be upgraded to Enhanced DRC operation with a software version of 2.X. (the X merely indicates the latest release and any upgrades). The software upgrade can be factory installed or upgraded in the field with the appropriate retrofit kit. The field retrofit kits are frequency sensitive since the PURC board contains wattmeter look-up tables which are not the same for all frequency bands and elements used in production. The Enhanced DRC software package allows the user to read and modify the station delay line setting, change the power alarm trip point thresholds, control station audio gain from -6.2 dB to +6.4 dB, and tweak transmit carrier frequency from 30 to 200 Hz depending on the frequency band of the station. The remote frequency adjust capability requires the station to have a paging synthesizer which has been modified to support this feature. In addition the user can remotely control 4 output wildcard bits for controlling third party site equipment.

7.7 PURC 5000 ADVANCED CONTROL
PURC 5000 Advanced Control is Motorola's next generation control hardware which replaces all of the standard control hardware in figure 10. The standard control which was comprised of a control tray, first expansion tray, and second expansion tray in some cases, was an initial paging control offering designed around the MSF 5000 two-way radio control tray hardware. The Advanced Control Tray is a completely dedicated paging control, eliminating unnecessary hardware and cabling that existed in the standard control of figure 10. The new design is microprocessor based and uses Digital Signal Processor technology for analog and binary audio processing. The tray is self contained in a 19" rack mount metal enclosure with pull out modules for easy of servicing. The hardware utilizes electronic potentiometers for alignment purposes thereby eliminating the need for mechanical tuning. The tray utilizes a 8 segment alphanumeric display to communicate with the user the station status, current hardware configuration, and settings of alignments. All local station access is performed via a 16 function key pad for scrolling through various station menus or entering numeric information for alignment and adjustment.

The tray is made up of 4 standard PC boards and an optional dial-up dial-out modem with battery backup for dial-up diagnostic capabilities. The ACB board is the main control board responsible for interface and control of the rest of the station. The ACB board contains all the audio and binary processing circuitry. The PSLIB board is a Power Supply Line Interface Board with generates local +5V for the tray logic circuitry. In addition the PSLIB provides interface for telephone line connects for incoming and outbound audio. The PSLIB board also supports the internal station dial-up dial-out diagnostic modem (optional) with battery backup (optional).

Both the ACB and PSLIB boards plug into a back plane board for easy field replacement. The back plane is screwed down to the metal tray enclosure and requires no service accesses. All interface cable connections are conveniently made from the front of the back plane board. The tray is sloped down towards the back allowing easy access to interface connectors. The Advanced Control Tray comes with an interface cable harness specially designed to minimize cable clutter. The Advanced Control Tray design no longer requires the tray to slide out on rails thereby reducing the risk of pinched cables as with the PURC 5000 control hardware in figure 10. As mentioned before all tray programming and station local access is accomplished via the Display board which has an 8 segment alphanumeric readout. Led indicators for critical station operating status indication, and a 16 function key pad for menu access and data entry. See figure 11 below for Advanced Control tray pictorial representation.

Figure 11

FIGURE 11. Advanced Control Tray Hardware Block Diagram

Advanced Control in PURC 5000 stations is only compatible with Simulcast stations. The tray does not support local alignment of binary deviation for Non-Simulcast stations as the PURC 5000 control hardware of figure 10 does. All binary deviation alignment is performed in the paging synthesizer tray for Advanced Control applications. The paging business has progressed primarily to simulcast systems and the required design effort to support Non-Simulcast stations was deemed impractical. Customers desiring Non-simulcast transmitters with Advanced Control will have no choice but to PURChase a Simulcast transmitter at the additional cost of the paging synthesizer hardware.

The Advanced Control Tray is currently offered with DRC control only, TRC control is currently under development. The tray supports both DRC 1 and DRC 2 messaging standard unlike the PURC 5000 standard DRC which only supports DRC 1 messaging. The tray also includes standard digital wattmeter hardware, digital delay line hardware, RS 232 interface hardware, and wild card input and output hardware. The digital wattmeter and delay line options are still paid for options. The wattmeter option will source the station a wattmeter element and the delay line option will cause the factory to enable the delay line hardware in software. Even though DRC is the only control format currently supported by Advanced Control it too is a customer paid for option. When TRC development is completed it will be the standard shipping control unless the DRC option is ordered. Consult the Advanced Control users manual, part number 6881084E80, for complete detailed tray operation. Consult SMR-5861 for hardware schematics and troubleshooting information.

FEEDBACK PATH FOR INFORMATION FROM BASE STATIONS TO CONTROLLER

8.0 INTRODUCTION
In order for an exchange of information to take place between the controller and the base station, a feed back path must exist from the base station to the controller. Two basic types of communications paths may exist. The first is a dedicated one-way return path, RF or wire line, from the base station to the controller. The controller then uses the outbound control channel to talk to the station and the station responds on the dedicated return path. The second type of return path is a separate bi-directional communications medium such as a dial-up phone line, whereby the controller can connect and communicate with the station without inhibiting the outbound station control channel.

8.1 RF RETURN PATH
An RF return path requires the use of a receiver on the paging transmitter carrier frequency as well as dedicated return wire line to pass the station diagnostic audio from the receiver location to the controller location in the event they are not co-located. Typically one receiver is unable to hear all the transmitters in a simulcast system, therefore additional receivers and wire lines are required to provide coverage for the entire system. The receiver return phone lines must be individually selected in the event that a transmitter can be heard by multiple receivers. In this type of situation a collision of the return information would occur from multiple receivers if the audio was merely summed together by a phone line combiner at the controller site. When installing this type of system, the base stations must be aligned and configured for over the air diagnostics.

8.2 SPECTRATAC MONITOR RECEIVER VOTING COMPARATOR SYSTEM
The SpectraTac Voting Comparator system is the only current product offered by Motorola for RF return diagnostics. The system was originally designed for two-way mobile systems which used it to monitor voice transmissions from mobiles. For diagnostics the system passes MDC DRC messages and voice quality is not an issue. Receiver selection is performed automatically by the Voting Comparator. If multiple receivers return diagnostic information from a single transmitter then the voting comparator selects the receiver that has the best Signal to Noise ratio. This ensures the greatest chance for MDC message recovery without the concern for data collision. The voting process provides us with the necessary receiver selection so that data collisions do not occur. A limitation with the voting process does exist however. In the event of a co-channel user or receiver interface a situation can exist when the wrong receiver is voted at the same time a diagnostic request is in progress. In this scenario the controller will get a "no response" from the station. Another diagnostic poll will be required to communicate with the station. The SpectraTac system was first used with the release of standard DRC in both PURC 5000 and Micor DRC stations using a DDC controller. See FIGURE 12, 13 & 14 below for detailed equipment operation.

Figure 12

FIGURE 12. SpectraTac Total Area Coverage System with Voting Comparator and Monitor Receivers

The SpectraTac Voting Comparator can support up to eight receivers per card cage. Up to three Voting Comparators can be connected together to allow up to 24 receivers to be supported in a voting configuration. The SpectraTac system also provides a return phone line check for continuity. When the receiver is squelched it sends a continuous tone of 2175 Hz., referred to as status tone, down the phone line. The voting comparator detects the presence of this tone and any loss of this tone without audio activity implies a break in the return phone line. The user is visually made aware of the failure by a led indicator.

8.3 SPECTRATAC MONITOR RECEIVER
The SpectraTac receiver comes standard with an audio control module (WL) and has three additional module slots for optional hardware. The audio control module contains line driver circuitry so that demodulated receiver audio and status tone audio can be sent to the Voting Comparator or controller for processing. The user can set the level via a front panel level set potentiometer. The coded squelch module (SQL) is not used for paging system applications. The module would be used if the transmitters used PL or DPL on transmit audio as is common in two way mobile system applications. The encoder module (ENC) provides status tone and should be ordered for phone line failure indication capabilities. The module is also used in properly aligning and characterizing the return phone line audio level when used with a SpectraTac Voting Comparator. The speaker and metering module is a local service interface for listening to recovered audio and aligning the receiver locally. This is optional, but recommended. Detailed information regarding receiver operation can be found in Motorola manual publication 6881039E45, SPECTRA TAC Total Area Coverage Voting and Satellite Receivers.

Figure 13

FIGURE 13. SpectraTac Monitor Receiver Block Diagram

8.4 SPECTRA TAC VOTING COMPARATOR

Figure 14

FIGURE 14. SpectraTac Voting Comparator Block Diagram

The Voting Comparator can support up to eight monitor receivers. Each receiver phone line is connected a Squelch Quality Module (SQM) which checks for status tone and performs the audio quality check when a voting situation occurs. The SQM provides led display for status tone fail, module voted, and un-squelch indicate. The module can be locally disabled or monitored. The Command Module (CMD) routes the voted SQM module audio to a 600 ohm line driver. The Voting Comparator command module audio can drive a phone line or connect directly to the controller if co-located. Typically the voting comparator is co-located with the controller. Up to three voting comparators can be connected to allow for up to 24 receivers to be supported for voting on a single system. The Key module is used to key a DC or TRC transmitter for re-broadcasting comparator voted audio. This capability is not commonly used in the paging system however there is no restriction on using it. As mentioned earlier most voting comparators are co-located with the controller and do not require a RF hop to the controller site. For further detailed Voting Comparator information see Motorola publication 6881039E50, SPECTRA TAC Total Area Coverage Comparator.

8.5 SPECTRA TAC USAGE FOR AUTO EQUALIZATION WITH THE ASC 1500
Voting Comparator Special Applications and SQM Module Concerns: The SpectraTac Receiver and Voting Comparator system is currently used for automatic delay equalization when using an ASC 1500 with Advanced Control paging transmitters. The automatic delay equalization system imposes special restrictions on the SpectraTac system. For diagnostic messaging, voting is allowed, however for auto delay equalization the receiver SQM's must be selected to insure system integrity for the equalization algorithm. Some stations may be able to hear two or more receivers with an equal quality level therefore the receiver used to return information may vary. For diagnostic messaging this is not a problem. For auto equalization however it is critical that the transmitter always pass audio through one specified receiver. The automatic equalization algorithm measures audio delay in closed loops comprised of the outbound control path, the transmitter, a SpectraTac receiver, and the receivers associated return phone line. If the SpectraTac receiver was not the same for each measurement made, the readings would vary due to the different return phone lines and the equalization algorithm would not be able to equalize the system properly. To guarantee consistent receiver selection the ASC 1500 utilizes the SpectraTac Voting Comparator SQM module inhibit capability to deselect all receivers except the receiver that pairs up with the station under test. The ASC 1500 can select/deselect up to eight receivers. This places a limitation on the system since equalization cannot be performed on systems needing more than eight receivers yet. The ASC 1500 uses the voting method for receiver selection when performing station diagnostics, only for equalization measurements is the select/deselect mode used.

The Squelch Quality Module was originally released as a TLN1718B kit and since then has been replaced with a TLN1718C kit. The C version module redesign included changes to the inhibit module logic circuitry which inadvertently created problems for use with auto equalization. C version modules are acceptable for standard voting applications however they cannot be used with the ASC 1500 for automatic delay equalization since the ASC cannot control the C version inhibit function. As a short term alternative the original module was brought back into production under an new kit number, TRN6091B. The TRN1718B SQM module or the TRN6091B module must be used for systems using an ASC 1500 and running automatic delay equalization.

8.6 WIRELINE RETURN
A wire line return path for diagnostic messaging requires each transmitter to be equipped with a dedicated audio phone line, comparable to a 3002 line grade, connected to Line 2 of the station. The station must be configured for wire line diagnostics, and the line 2 driver must be adjusted for a level less than or equal to the maximum allowable level tolerated by the phone company. Typical levels are -5 to -10 dB. All these wire lines must then be combined using third party telephone combining equipment to feed the audio diagnostic input on a DRC controller. Typically a combiner with independent gain control is used so that the phone line loss from each site can be compensated for to produce a consistent input level to the controller. Phone lines can vary in loss anywhere from 0 to 15 dB in the course of a day. In the event a large phone line loss is noticed, i.e. a transmitter no response occurs, the gain in the combiner can be increased to temporarily compensate for the loss and restore diagnostics while the phone company is alerted to check the line and correct the problem.

The dedicated wire line return path can also be used for Unsolicited Alarm Reporting when an ASC 1500 and Advanced Control base stations make-up the system. Stations capable of unsolicited alarm reporting will send MDC messages to the controller when an alarm condition is detected. Since all the return wire lines are combined together, it is possible for two or more stations to be sending information and have the data corrupted by a data collision. To alleviate the problem of data collisions, the stations will continue sending alarm messages in a random fashion until the controller services the alarm with an acknowledge to the station. This acknowledge requires the control channel to be inhibited from paging while the ASC 1500 services the station.

8.7 MODEM CONNECT VIA THE PUBLIC SWITCHED TELEPHONE NETWORK
Both the RF and wire line return system configurations impose a restriction on the outbound control channel in that when diagnostics are performed paging is inhibited. An alternative to this type of system configuration is to use a form of diagnostic messaging referred to as Dial-up/Dial-out diagnostics. This type of system requires the controller to support and be equipped with a Hayes 212 compatible modem and a dial up phone line. Each transmitter must also be equipped with a dial-up phone line and a modem. This type of system configuration allows paging and diagnostics to run in parallel and on independent channels so the control channel is not inhibited during diagnostics. An addition benefit of this type of system is the ability of the base stations to initiate a message when a failure is detected as opposed to waiting to be polled at some time interval by the controller. This type of system operation is referred to as Unsolicited Alarm Reporting and is a form of real time alarm reporting. The only delay is the delay in the modem dialing and connecting via the telephone network. The phone system inherently performs data collision avoidance between transmitters since a station trying to dial the controller will get a busy signal if the controller is servicing another station. A station which is busied out will continue calling the ASC until the alarm is reported and the ASC acknowledges the alarm.

END OF SECTION
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