Notes on the hookup of a Motorola
Spectra TAC (Total Area Coverage) Voting / Satellite Receiver

By M. Scott Zimmerman N3XCC

Disable the signaling in a Spectra TAC commercial Voting Receiver for use in a non-commercial installation. Also describe the common receiver connection points on the unit for direct connection to other radio equipment. I.E. a link radio or repeater controller.

The Motorola Spectra TAC voting receiver is a compact single chassis receiver solution for remote voting applications. It was intended to be used with wire line interconnects between the voting receiver and the voting panel.

Since the system was designed for wire interconnects, or constant key radio links; all telemetry (S/N ratio, COS active, etc.) was transferred by using tones and/or DC voltages. For most amateur applications dedicated phone lines are cost prohibitive and full time radio links don't allow for efficient use of available spectrum.


The following signals are available from the Spectra TAC receiver:

Signal Name Module Name
Pin Number
Discriminator Audio1
Audio Control
Un-squelched, Un-filtered Discriminator Audio. Direct from Discriminator
Buffer Disc. Audio2
Audio Control
Buffered, Un-squelched, Un-filtered Discriminator Audio
Amp. Disc. Audio3
Audio Control
Amplified, DC Biased, Un-squelched, Un-filtered Discriminator Audio
De-Emph. Audio4
Audio Control
De-Emphasized, PL filtered audio. Fed through a 22K series resistor. (see below)
Audio Control
Ground When Squelched, Open when Un-squelched. May require a pull-up resistor.
PL/DPL Decode
Audio Control
16 & 21
Each pin is a separate source of 13.8v when correct tone is decoded or disable switch is activated.
PL/DPL Decode module must be installed.
    Pins are counted from the top of the module toward the bottom.
  1. This audio is direct from the receiver's discriminator output and will provide approx. 500mV P-P audio.
  2. This audio is DC biased at approximately 5.5V DC and will provide approx. 500mV P-P audio at low drive impedance.
  3. This audio is DC biased at approximately 4V DC.
  4. This audio is DC biased at approximately 3.7V DC. It has been De-Emphasized and PL filtered and is fed through a 22K series resistor. This source impedance may cause low audio problems in some applications. The 22K resistor can be simply shorted out to eliminate this problem. Simply follow the circuit board trace backward from pin 15. You will easily find the 22K resistor in question. Also, this point is DC coupled to the audio circuitry. In most cases, when feeding a repeater controller, the controller's input will be capacitively coupled and will not be a problem. However, if it is not, you MUST add a series coupling capacitor to block the DC voltage from upsetting the controller's audio circuitry. All telemetry cards (I.E. Signal Quality Module, Spectra TAC Encoder Module, Etc.) need to be removed before using this pin. In most applications these modules are not needed anyhow.
The above connection points assume that you are using an Audio Control Module and, if applicable, a PL/DPL Decode Module. If the Audio Control Module is not being used, Pins 3, 10, 11 and 15 will not work as described above. This is because the audio amplifier circuitry and squelch circuitry are located on the Audio Control Module. If you don't have an Audio Squelch Module, all is not lost, but you will need to build your own audio amplifier and squelch circuits.

The only module that is required for most applications is the Audio Control Module. The PL/DPL decoder card may be required if you are planning on using one of those sub-audiable tone types. The rest of the module positions are not used and should be left empty. The only other module that my be used is the Receiver Service Module. This module is great for monitoring the receiver's audio and properly aligning the receiver. If one is not available, it's not a problem. They are just nice to have.

As always, more information can be found in the Motorola service manual. The part number for this manual is: 6881039E45.


Copyright 7-14-2005 M. Scott Zimmerman, N3XCC
This information was compiled by M. Scott Zimmerman, N3XCC    7-14-2005
Page last updated by N3XCC 7-14-2005

Up one level
Back to Home