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The Motorola SpectraTAC™ Receiver, Satellite Receiver and Auxiliary Receiver
Compiled by Mike Morris WA6ILQ
(see the notes at the bottom of the page)
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
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:
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).
- 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).
- 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.
- 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)
- 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).
- 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.
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
120 / 240vAC
800 or 900 MHz
Typical model number: C04RTB-3108C
- 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.
- Since there is no transmitter, the transmitter power output indicator digit is
- 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
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.
- 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.
- 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.
- 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).
- 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.
- 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:
- Slot 1: The "Audio Control Module" is a TRN6080A or B (low, high or UHF) or a
TRN6598A or B (800 or 900 MHz units)
- Slot 2: either the TLN5946A "Receiver Quality Signal (RQS) Line Current Generator"
card or the "Coded Squelch Module", which could be either:
- TRN6082A or B for DPL (uses a TRN6005 to set the DPL code, and there is a
page at this web site that shows you how to build up your own code plugs)
- TRN6083A or B for PL (uses a TLN8381 reed - the same as a MICOR)
- Slot 3: either the TLN5946A "Receiver Quality Signal (RQS) Detector Module" or the
"Encoder Module", which could be either:
- TRN6085A or B is the "SpectraTac Encoder Module", which sends 2175 Hz down the
line while the receiver is squelched, or can send one of two test tones (400 Hz or 2500 Hz)
for testing line equalization.
- TRN1460A "Voting Encoder Module", which sends either or both of 2250 or 2325 Hz
tones to indicate one of three receiver quieting levels (this was the older two-tone
voter that could not handle fluttery or fading signals).
- Slot 4: The "Receiver Service Kit" consists of the TRN6087A / TLN1717A
metering module (Click for side view),
plus the TKN6759 cable kit that connected the metering card slot to the metering
connector on the receiver circuit board. The two items together comprised Option
C105AA in the order book. If you are going to add metering to a chassis you need
BOTH the card and the cable, the cable is not common in surplus, and the connector
that plugs into the receiver card is no longer available. Why two numbers on the
module? Don't know. The book calls for the TLN1717A module but the actual card is
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)
The TLB6851 is very, very rare, I've only seen one in my entire career.
Mid Band (Uses a K1003 channel element)
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)
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)
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)
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).
||Wideband, 5 kHz deviation, 25 kHz channel spacing, uses a KXN1029A
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 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).
- There is no AC power switch. More than one chassis has been modified with an
added toggle switch (on the rear).
- 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.
- Likewise, there is no indication of COR / COS / channel busy / a carrier present.
Another LED can be added next to the squelch potentiometer.
- 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.
- Moto made a special "Extractor Tool" to get the cards out of the MICOR chassis
or the Aux receiver chassis: part number 6683574F01.
- The tuning tool specified in the aux receiver manual is part number 6684387C01.
- 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.
- The "Receiver Interconnect Board" (that connects the receiver board to the
module motherboard) is TRN8538A.
- The "Module Interconnect Board" (the module motherboard) is TRN6090A.
- The TRN8625A is the shield kit, and consists of the 0180796B67 front cover
and the 0180799B72 rear cover.
- The TPN1158A is the power supply module (add this to a "RTA" or an "RTN" to
make it a "RTB" unit).
- 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.
- 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™").
- 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).
- 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.
- 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
- 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
- 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.
- 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.
- 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.
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.