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  The Motorola SpectraTAC™ Receiver, Satellite Receiver and Auxiliary Receiver Information Page
Compiled by Mike Morris WA6ILQ
(see the notes at the bottom of the page)
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First of all, this is NOT a Spectra! This is a Spectra TAC Voting and Satellite Receiver, sometimes called an Auxiliary Receiver.
The Spectra is a later design mobile radio and those radios have their own pages at this web site.

What's the connection between the MICOR and the Motorola Spectra TAC Voting and Satellite Receiver or the Auxiliary Receiver ?

The original design of the MICOR station had separate chassis for the receiver, exciter and control shelf, all linked by 50-pin ribbon cables. At that time multconductor ribbon cable and the insulation displacement connectors were a fairly new product and Moto had nothing but trouble with them. It wasn't long until Moto came up with a Unified Chassis design that eliminated the riibbon cables entirely (and after the the 50-pin ribbon cables and the insulation displacement connector products matured they lived on as the PC and mainframe SCSI-II disk drive intercabling).
Moto needed a second receiver for the unified MICOR chassis and the engineers took the early stand-alone MICOR receiver chassis and did some redesign. They came up with a package that could function as a stand-alone auxiliary receiver, as a second receiver, a third receiver, or even more (I've seen six in a single rack, each on a different channel and fed by a receiver multicoupler).
The first Moto-designed voter system used DC current in a phone line to indicate signal strength at the satelite receiver. This DC current system used cards designed for that purpose in slot two and slot three of the chassis. When the phone company started making DC lines very hard to get, if not ourtight impossible Moto came up with a system that mimiced the GE noise voter. That system, (called "SpectraTac") fit the voter encoder on one card and it went into slot three and slot two was used for the PL or DPL card. The fourth slot has always been for the metering / speaker card.

By the way, the "TAC" in " Spectra TAC" is translated as "Total Area Coverage" in Moto marketing-speak.

The receiver package covered on this page is a separate rack mount chassis that holds a standard MICOR receiver board (low band, mid band, high band, UHF, 800 MHz or 900 MHz), supporting PC boards in card slots, an optional metering card and an optional power supply. The card complement varied with the particular application - a simple receiver, an auxiliary receiver that drove a dedicated phone line, or a voting receiver that drove a microwave channel or a phone line. The cards themselves resemble those in a MSY, MICOR or MSR2000 repeater control shelf, however the cards are NOT compatible with a MSY, MICOR or MSR shelf, and neither the MICOR nor the MSR cards are compatible with the Satelite receiver / Aux Receiver / SpectraTAC shelf.

People unfamiliar with the product look at the chassis and see a model number TLN1991A or TLN1991B and think that they have a valid model number. They do, but what they have is for the rack-mounted bare sheet metal box. The TLN1991x is not a receiver. It is, according to Motorola, a "Receiver Housing Assembly" that is used for all models of auxiliary, satellite and SpectraTAC voting receivers.

As you can see from the above, an eBay listing that identifies this unit as a Spectra receiver just shows the lack of knowledge of the seller, and an an eBay listing that identifies a chassis as a "TLN1991 Receiver", a "TLN1991A Receiver" or a "TLN1991B Receiver" IS TOTALLY BOGUS - the TLN1991x is the sheet metal, and just the sheet metal!   To have useful identification of what you are bidding on you need:

  1. The factory model number (see the photo above for where to find it) is in the format of (letter)(digit)(digit)RT(letter)(dash)(4 digits)(one, two or three letters).
  2. The part number of the receiver board (they are in a three-letter-and-four number-and-a-letter-suffix pattern).   You will need to remove the shield cover on the left side of the rack to find it.
  3. The model numbers off ALL of the plug-in cards (they are in a three-letter-and-four number-and-a-revision-letter pattern, for example TRN6080A)
  4. If there is or is not a power supply module in the chassis (just look to see if there is a transformer visible in the hole in the back).
  5. If there is a metering card (it will be in the right-most slot), take the cover off the receiver board and see if there is a cable plugged into the metering connector on the receiver. If not, the metering card is useless.
If you have an exisiting chassis that does not have a metering card and buy one in surplus make sure that it comes with the metering cable, as it will be useless without it. If there is no cable then don't pay a lot for it (or plan on making up your own cable, and the special metering plug is no longer available).

No matter what the configuration, these chassis are useful as point-to-point link receivers, control receivers, or when you need to add a receiver to an ex-paging base station when you convert it into a repeater.

To go into more detail, the basic Aux Receiver is a chassis with a receiver, the common audio card (the left-most slot), an optional PL or DPL card (in the second slot), and an optional power supply. The only difference between an Auxiliary receiver and the SpectraTAC receiver is that the SpectraTAC version added the voting encoder card into the third slot, which is necessary for the chassis to handshake with the SpectraTAC voting shelf at the other end of the wireline or microwave link. In other words, the "Encoder Module" is useful only if you have a SpectraTAC voting shelf at the other end.

The receiver board used in any version of the chassis is a plain-jane MICOR receiver board, and all the other articles at this web site that cover modifications to the receiver board (i.e. mods for 2m or 220 MHz) are applicable. This also means that you can move a chassis to any band (as long as the receiver antenna coax connector matches - the low band, mid band, high band and UHF units used a chassis-mounted SO-239 antenna connector attached to an internal cable that terminates in an RCA plug that feeds the receiver card. The 800 and 900 MHz units use a type "N" connector, high grade teflon cable for the internal cable and an SMA connector for the receiver.

The chassis model number breaks down as per the table below - but realize that the receiver boards can be swapped in 5 minutes, and the model number on the chassis may not be accurate - really, you have to look at the actual TLB / TLC / TLD / TLE / TLF part number stamped on the receiver board.

Aux Receiver / SpectraTAC Receiver Chassis Model Number Breakdown
Numbers in [ brackets ] are references to the table notes at the bottom
Typical model number: C04RTB-3108C
Type [1]
Power [2]
Band [3]
Series Supply
Voltage [4]
30-50 MHz
66-88 MHz
132-174 MHz
120 / 240vAC
395-520 MHz
800 or 900 MHz
900 MHz

Typical model number: C04RTB-3108C
Type [5]
Deviation [6]
Frequencies [7]

Configuration [8]

(no card)
15 kHz
One Freq
(no voting
encoder card)
(PL card
5 kHz
Two Freq
(voting encoder
card added)
(DPL card
2.5 kHz
Four Freq

Table Notes:

  1. The leading "B" indicates a Base station cabinet, a leading "C" indicates a Compact series cabinet, a leading "N" indicates no cabinet was shipped with the unit.

  2. Since there is no transmitter, the transmitter power output indicator digit is always zero.

  3. Do not trust the band indicator in the model number as it takes 5 minutes or less to swap a receiver card in the field. Always look at the part number on the actual receiver board when evaluating any surplus unit. Each of the frequency bands are divided in frequency ranges (called "splits") and any given receiver card was built for a specific split (like 42-50, 132-150.8, or 450-470 MHz). If you are buying a surplus chassis make sure that you purchase one containing a receiver card made for the split you need (or plan on range-changing the card you have, or swapping the receiver card). Note that the receiver audio card (the left-most slot) is different between conventional and trunking - i.e. a receiver that was configured for 800 MHz may require some mods to the audio card before you can make a 150 MHz or 450 MHz receiver work properly. Also make sure that the receiver comes with the proper channel element included - I've seen a receiver chassis that was purchased on eBay with a UHF PL model number that arrived with a 150 MHz receiver board, a trunking audio card (in the left-most slot), no PL card and a 33 MHz channel element. And the seller advertised it as a UHF PL receiver "recently removed from commercial service". Yeah, sure... It was obviously a frankenstein (i.e. build up from spare parts). For more information see the table of MICOR receiver board part numbers below.

    Another point: These units were manufactured during the time period that band 5 included both 800 MHz and 900 MHz, and after the transition that created band 7. So a surplus band 7 unit was definitely shipped with a 900 MHz receiver board, but a band 5 receiver chassis could be configured for either 800 or 900 MHz, and it could be trunking or conventional.

  4. The "A" series chassis do not have a power supply module installed (it can be added in the field) and are dependent on another source of both +12vDC and +9.6vDC, be it a MICOR station in the same rack, or an adjacent "B" or "K" unit. Many surplus units have had the power supply removed, so make sure that if you are buying a surplus chassis and need to power it from the AC mains that it has a power supply installed. The "K" configured chassis are very rare in the USA. In most cases the "N" units were the same as "A" units - they required an external source of both +12vDC and +9.6vDC. See below for some comments on modifying a chassis for +12v-only operation.

  5. Changing from carrier squelch to coded squelch (i.e. PL or DPL) requires you to plug in the appropriate Coded Squelch card. Changing squelch types involves changing out the squelch card. Do not trust the chassis model number, always look in the second card slot. Make sure the card is a SpectraTAC or Aux Receiver card, it is unique to this chassis, a MICOR station card or a MSR2000 station card will not work. Also the same blank PC card was used for both tone and DPL, one half was stuffed for PL, the other half for DPL (see this photo). You can add the missing parts and have a combination card that will decode both tone and DPL on an OR basis (i.e. either the proper PL tone or the proper DPL code will unsquelch the receiver), or add a SPDT toggle switch and have it be one or the other. WA1MIK wrote an article on how to add DPL to a tone PL card using an aftermarket DPL decoder card.

  6. A "0" is a very rare beast as the market for wideband radios is very limited. It was a special order for the broadcast industry as some stations had wideband VHF and UHF remote pickup channels. 99.9% of the time you will find a "1" in this position. If you find a "2" it indicates that the original receiver was configured for 2.5 kHz deviation (i.e. 900 MHz).

  7. Finding anything but a zero in this position is rare, but adding additional frequencies is no different and no more difficult than on any other MICOR receiver. A factory single frequency chassis will have an internal jumper that connects the Frequency #1 (F1) control line to ground.
    All MICOR receiver boards support either 4, 8 or 12 channel elements, but there was no mention in the model table in the book I looked at for a 8 or 12 frequency receiver - from the model table you would think that the highest channel count was 4. It may be that the Aux Receiver chassis is limited to 4 channel receiver boards.

  8. There are other configuration options (not listed) that include the presence of an optional double-wide metering card (that includes an audio amplifier and a loudspeaker) which goes in the right-most slot. If anyone has any additional configuration options information please let me know and I'll add them to the table.

Here's a photo of the rear of the chassis. This particular one has a BNC-to-N adapter screwed onto the antenna jack. There is also provision for plugging in a handset to allow communications with another technician at the SpectraTAC voter site. Some documentations refer to this as the "order wire" option.

Many surplus receiver chassis have a self-contained AC mains power supply that has two power connections - the chassis-mount one that is for the incoming power line, and a pigtail lead output. The power cord pigtail allows daisy-chaining of the AC power cords between units. While you could theoretically daisy chain an entire rack of receivers, the manual says one power cord for three or less receivers. Personally I don't like daisy-chaining - I run a separate cord from each chassis to a power strip. Murphys Law says that the receiver that dies will be the first in the chain, requiring you to shut down the entire string of receivers to remove the dead one.

As mentioned above the chassis versions that are missing the power supply ran from external sources of +12vDC and +9.6vDC. You can add a +9.6 regulator to make your chassis dependent on +12 only. Simply bolt an LM340-9 or 7809 (a +9vDC three-legged voltage regulator) down to the chassis with the appropriate bypass capacitors and a silicon diode in the ground lead (raising it to +9.7 volts) or a LM340-8 or 7808 (a +8vDC regulator) with two diodes (+9.4 volts). Personally I'd look at the LM117 / LM317 series of regulators. If anyone would like to do an article on that mod please consider this an invitation - we'll publish it.

The cards that plug into the unit are dependent on the application. The Voting Receiver or the Auxiliary Receiver systems used the Coded Squelch and Encoder cards, where an IMTS mobile telephone system used the TLN5946A "Receiver Quality Signal (RQS)" cards. The possibilities were:

Known MICOR Recevier Part Numbers:     If anyone wants to donate a board photo we will put it up here.

Low band:         (Uses a K1003 channel element)
Part Number Range
TLB6851 25-30 MHz
TLB6852 30-36 MHz
TLB6853 36-42 MHz
TLB6854 42-50 MHz
The TLB6851 is very, very rare, I've only seen one in my entire career.

Mid Band         (Uses a K1003 channel element)
Part Number Range
TLC6112 72-76 MHz
The frequencies below 72 MHz and above 76 MHz in the USA are TV channels. Most of the 72-76 MHz frequencies are used as commercial point-to-point links. The "official" mid band is 66-88 MHz worldwide. Later Moto products covered the mid band as two splits, 66-77 and 77-88 MHz.

High band:         (Uses a K1005 channel element)
Part Number Range
TLD4071 132-142 MHz
TLD4072 142-150.8 MHz
TLD4073 150.8-162 MHz
TLD4074 162-174 MHz
Overall, range 3 is the most common in surplus. Most railroad radios are range 4.
All MICOR highband receivers have the same ranges, so I'm only going to list one in the above table.
The TLD827x is a 4 channel receiver and the most common. The TLD827x is an 8 channel receiver and most often found in mobiles. The TLD578x is a 8 channel receiver that was found in a VHF DVP (Digital Voice Privacy, a form of scrambling or encryption) station, it may be used in DVP mobiles as well. The TLD845x has the extender noise blanker option - rare on high band.
The TLB8271 and TLD8272 are very, very rare, I've only seen one of the 8271 and it was on a 142.7 MHz Shore Patrol channel (yup, out of band). I've seen a few of the TLD8272 and they were in Civil Air Patrol repeaters (the input was around 143 MHz).

UHF:         (Uses a KXN1024 channel element)
Early ID Late ID Range
TRE1201 TLE8031 406-420 MHz
(skipped) (skipped) 420-430 MHz
TRE1202 ? 430-450 MHz
TRE1203 TLE8032 450-470 MHz
TRE1204 TLE8033 470-494 MHz
TRE1205 TLE8034 494-512 MHz.
? TLE8035 512-530 MHz.
The TRE1202 is very, very rare, and only found in European systems (the business / commercial band starts at 440 MHz in Europe and the UK), or where a MICOR was factory ordered on amateur channels in the USA. The 420-430 MHz range is skipped over in the factory stock receiver boards. The TLE8035 receivers that I've seen were all on 520-530 MHz frequencies and they are not in the standard manuals.

800 Band (806-821 MHz)         (Uses a KXN1029 channel element)
Part Number Range
TRF1011 806-821 MHz

900 MHz
Part Number Range Notes
TRF1032 928-960 Wideband, 5 kHz deviation, 25 kHz channel spacing, uses a KXN1029A Channel Element
TRF6112APR 900 MHz  
Note that there were wideband (5 kHz) and narrowband (2.5 kHz) receivers built for 900 MHz. I don't know the specs on the TRF6112 receiver (i.e. wide versus narrow).

Spectra TAC Encoder Option for MICOR Stations:

A standard remotely-controlled MICOR base or repeater station can be modified to put out the idle status tone when no carrier is received, thus allowing it to participate in voting with a Spectra TAC comparator. This is called "Option C269" and it requires installation of three boards into the MICOR card cage. There are four relevant documents that cover this option; each is about a 250kB PDF file.
Spectra TAC Option C269, main description
Spectra TAC Encoder Module, TRN6085B1
Spectra TAC 4-wire Line Driver Module, TRN6552A
Spectra TAC Squelch Gate Module, TRN6689A

Spectra TAC Voting and Satellite Receiver Instruction Manual, 6881039E45, about $12 in Feb. 2007.
Spectra TAC Comparator Reference Manual, 6881039E50, also about $12 in Feb. 2007.
The later Spectra TAC Voting and Satellite Receiver Instruction Manual contains full specs, installation, maintenance, troubleshooting, schematics, board layouts, and parts lists for the receivers, all plug-in modules, the power supply, and the chassis / backplane. There are sections in the manual for VHF low-band (25-50), mid-band (72-76), and high-band (132-174), UHF (406-512), and 800 MHz (806-821) receivers. The later revisions contain the information for the 900 MHz receiver board and has the updates to the audio and receiver cards.
The 900 MHz PURC service manual, part number 68P81062E70, also has the info on the 900 MHz receiver. The price in 2004 was about $10.
The MSF5000 Link Reciever Options manual (part number 68P81063E10 (I have a "B" version)) has the info on the 72-76 MHz receiver (option C661), the 450-470 MHz receiver (option C659 and C662), and the 900 MHz (receiver (option C660 and C663).

Additional Info:

  1. There is no AC power switch. More than one chassis has been modified with an added toggle switch (on the rear).
  2. There is no indicator that power is applied to the chassis. A front panel power indicator can be implemented on the audio control module (which is necessary for a functional receiver - every other module is optional). Simply add a green LED above the word "RCVR" at the top of the card, with a series resistor from the +12v pin to the LED, and ground the other side of the LED.
  3. Likewise, there is no indication of COR / COS / channel busy / a carrier present. Another LED can be added next to the squelch potentiometer.
  4. The LED on the PL or DPL decoder card is not a decode indicate LED. It is switched on by one pole of the disable switch (i.e. it is in carrier squelch when the LED is on, and in PL or DPL when it is off). A common mod is to do one of these:
    1) rewire the LED as a decode indicator, or
    2) relocate the red disabled LED to just above the disable switch, and in the newly vacated hole (where the LED used to be) add green LED wired as a decode indicator.
  5. Moto made a special "Extractor Tool" to get the cards out of the MICOR chassis or the Aux receiver chassis: part number 6683574F01.
  6. The tuning tool specified in the aux receiver manual is part number 6684387C01.
  7. The extender card for servicing the modules is listed as a 0180700B25 in one manual and as a TLN8799A in another. The PCB itself is etched with the number 84E83959G01 but that's the bare circuit board, not the assembly of board, male and female connectors (an 84-series part is a bare PCB, in general an end user cannot order one. Even the Motorola National Service Organization shops are given a hard time when they try to order one). A couple of useful mods: add one series LED and resistor set on the 12vDC and a second set on the 9.6vDC buss. Second mod: cut the main +12 and +9.6 power trace and put a fuse holder across each cut. When you have a shorted card you can pop the fuse and put a miliammeter across the fuse holder, otherwise you can put a fuse in it.
  8. The "Receiver Interconnect Board" (that connects the receiver board to the module motherboard) is TRN8538A.
  9. The "Module Interconnect Board" (the module motherboard) is TRN6090A.
  10. The TRN8625A is the shield kit, and consists of the 0180796B67 front cover and the 0180799B72 rear cover.
  11. The TPN1158A is the power supply module (add this to a "RTA" or an "RTN" to make it a "RTB" unit).
  12. The power supply is a single AC voltage unit, built for either 120vAC or 240vAC. There are no jumpers, to change mains voltage you replace the transformer.
  13. Option C28AB added the TPN1141A "Emergency Power Kit" which consisted of nothing but a 12v 8ah gell-cell and a 2a fuse between the + and - terminals on the module backplane. All of the AC power supplies had the charger circuit (R108, a 20 ohm resistor, set up as a constant voltage charger. If you value your battery life, remove that resistor and use a modern external charger designed for maximum battery life (like a "Battery Tender™").
  14. The VHF/UHF antenna cable (N to RCA plug) is a TKN6998A, and the 800/900 MHz cable (N to SMA) is a TKN6999A. If you are going to install an 800 or 900 MHz receiver into an existing VHF / UHF chassis you will have to locate (or manufacture) a TKN6999A cable (or cheat and make or acquire a female RCA to male SMA adapter cable).
  15. The chassis offers an intercom function between the receiver location and the other end of the wireline circuit. This required a TMN6067 handset to be plugged into the backplane connector labeled "handset". The handset was Option C192AA in the order book.
  16. Option C12AE adds either the TLD8421 preamp (136-150 MHz) or the TLD8422 preamp (150-174 MHz) and the associated TKN6807 cable kit. This 10 dB gain preamp (according to the book) bumps the receiver sensitivity from 0.5uv to 0.25uv. Frankly, AngleLinear makes a better preamp. See the MICOR page at this web site for details.
  17. Option C12AD adds either the TLE8191 preamp (406-450 MHz) or the TLE8192 preamp (450-512 MHz) and the associated TKN6812 cable kit. This 10 dB gain preamp (according to the book) bumps the receiver sensitivity from 0.5uv to 0.25uv. Frankly, AngleLinear makes a better preamp. See the MICOR page at this web site for details.
  18. Speaking of preamps, the metal bracket that mounts the preamp on the back of the receiver chassis is a 15D8366K03, however the same cover in the manual shield kit gives it the part number 1V80799B72. It is part of the TRN6825A Receiver Shield Kit. This plate mounts on the rear of the receiver housing to cover the power supply. The cable from the chassis mounted antenna connector feeds the preamp input, the cable shown should be plugged into the output connector and is used to feed the receiver front end.
  19. Option C2466 added a TLE1082 6-port UHF antenna multicoupler to allow one antenna to drive multiple receivers, but at a cost of some considerable insertion loss. You would be much better off if you used a preamp-based multicoupler. You will want to use 50 ohm terminations on any unused ports. The book does not list a high band multiport coupler.
  20. Do not use the audio output of the metering card to feed your Sinadder for tuning a receiver. The design of the audio amplifier on the card has a serious amount of distortion and it will really confuse the Sinadder and you will think that the receiver is much worse than it really is.

Contact Information:

The author can be contacted at: his-callsign // at // repeater-builder // dot // com.

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This page created 05 October 2008 by Mike Morris WA6ILQ

The author would like to acknowledge the contributions from from several submissions to the Repeater-Builder mailing list, and from conversations with several hams that have battled the quirks of the Aux Receiver chassis.

Motorola® and SpectraTAC® (and a bunch more stuff) are registered trademarks of Motorola Inc.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.