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Communications Specialists TS‑64MSTII Modification
This article is based on a privately circulated writeup authored by Douglas Sharp K2AD
Dougs version of June 20, 2002
HTML'd and edited by Mike Morris WA6ILQ

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The Communications Specialists TS‑64MSTII is a "motherboard" that adapts the TS‑64DS (which is already a two-board stack) so it plugs into the MASTR II station in place of any of the several different stock GE "Channel Guard" (CTCSS) boards. Not only does it allow a carrier station to be converted to CTCSS without the hassle of locating a stock CG (CTCSS) board, but it also adds functionality - the stock board is either a decoder or an encoder, but not both at the same time...
As most stations these days need decode and frequently both encode and decode at least one function has to be added on by a third party board, and frequently both. The TS‑64MSTII provides decode, encode, a timeout timer and the high-pass audio filtering (which removes the received tone from the receiver audio) all in one board, and it is readily available (which can't be said for the GE board, even if it had all those functions) for around US$70.00.

A note from WA6ILQ:
The only limitation is that this configuration can't do split tones... i.e. it decodes and encodes the same tone.

The relevant Com-Spec manuals are here: (all except the last one are links to other pages at this site)

Note:   Com-Spec will sell direct to the end user and can easily beat Hutton's, Tessco's and most others prices.
Call 800-854-0547 or 714-998-3021 from 8:00am to 4:30pm (Pacific time zone), Monday to Friday

Once you have your TS‑64MSTII board in hand this modification makes the board and station combination much more usable.

The Communications Specialists TS-64 CTCSS Encoder / Decoder

Communications Specialists TS‑64 Wire Colors
1 Red DC power in (+8vDC to +20vDC). Worst case current draw is 9 to 10 milliamps.
2 Grey PTT Output - this is an open collector that goes to ground to enable the transmitter. This signal is the ORed result of the PTT Input plus the 160ms squelch tail elimination delay. In repeater service you will run this lead to the PTT input of your repeater transmitter.
3 Black Ground (both logic ground and audio ground)
4 Green Audio input - feed this pin with discriminator audio from the repeater receiver. It is the input to both the tone decode circuit and the receiver audio filter circuit (see the blue wire note below). This is a high impedance input (50-60k ohms) that needs at least 15 millivolts of audio.
5 White Receive audio mute - While this pin is labeled as "audio mute" it's actually an open collector logic level output which goes active when the subaudible tone is decoded. This pin can be set for active high or low (configured with JP7) and is factory default active low (goes to ground when the tone is decoded). If your repeater controller has separate COR and Tone Decode inputs this goes to the Tone Decode input. If it has only one input then this pin is used as that signal.
6 Yellow Encoder tone output (low impedance) - Up to 3 volts P-P of audio is available here, controled by the PTT input (the orange wire mentioned below).
7 Blue Filtered audio output - The path between the green wire (in) and the blue wire (out) has a high pass / low cut audio filter in line, designed to remove the subaudible tone from the user audio. The signal from this pin gets sent to the repeater controller audio input (when using an external controller) or to the transmitter if not.
8 Orange PTT Input - when pulled to ground this pin enables the tone encoder and puts the TS‑64 into transmit status (keys the PTT out lead and switches the tone encoder on). When ground is removed the output tone is phase shifted for 160ms, then the tone is switched off. In an environment with an external repeater controller you would use this pin to control the encoder. The PTT out (pin 2, grey) goes to the transmitter PTT in.
9 Violet This is a dual mode connection, and the mode depends on JP11. In repeater service you will want to leave JP11 open (which is out as the module comes from the factory).
  • JP11 out: This lead is the HANGUP input. In normal mobile service it is connected to the microphone clip so that it is grounded when the mic is in the clip (enabling the tone decoder) and floating when the mic is out of the clip. This behavior forces the mobile user to monitor the channel in carrier squelch mode before he keys up.
    If your prepeater controller has a single COR / Tone Decode input this lead could be run to a repeater controller switched output: floating is carrier squelch, grounded is in CTCSS decode mode. Since our application is full time CTCSS decode mode we jumpered this lead to ground on our TS‑64MSTII module.
  • JP11 in: This lead is a channel BUSY input and is connected to a point that goes high when the squelch is open (high is defined here as anything between 1.5vDC and the DC voltage input to the TS64). When the BUSY input is high the PTT is inhibited. This behavior is usually used on mobiles to prevent one user from doubling on another in a simplex environment. More details on connecting this input lead is in the TS‑64 manual.

Project Steps:

  1. Install the TS‑64 onto the TS‑64DS if it didn't come that way, and it on the TS‑64MSTII board if it didn't come that way. Yes, you will end up with a 3-board stack.
  2. Cut the jumper wire between “PTT DELAY” pins (the 6th and 8th from the left) and remove the stub ends from the holes in the board. Opening the jumper enables the "Squelch Tail Elimination" (sometimes called STE). The Motorola addicts would call it "reverse burst".
  3. Cut the blue, orange and grey wires near the "top connector". These cuts are visible in the enlarged Photo 1.
  4. Route the blue, orange and grey wires as shown in the drawing below and solder.

Click on the photos below for a larger image

Photo 1

Here is a photo of the assembly installed in the station.

Photo 2

Any of the LBIs (service manual sections) mentioned below can be downloaded from the LBI Library here at www.repeater-builder.com.

Station Modification Steps:

  1. Jumper changes to the 10 Volt Regulator Board:
    1. Insert a jumper between H2 and H4.
    2. Insert a jumper between H3 and H9.
    The two jumpers above configure the PTT timing for the delay involved with the squelch tail elimination. Additional information about how these jumpers affect the operation of the Station can be obtained from LBI-30704. One useful mod to the card: add a green LED for the presence of DC power, and a red LED for transmit indication (i.e. PTT).

  2. Jumper changes to the Receiver System Board:  (See Figure 1 and Figure 2 below.)
    1. Remove the jumper between H41 and H42. This disconnects the receiver audio mute signal (called RX MUTE in the manual) from P908-5, which keeps the receive audio on during transmit. This is standard in Repeater Stations, per the notes in LBI-31899. Other jumper changes on the System board may be required if the Station was not originally configured for Repeater operation.
    2. Cut trace between P908-2 and J952-8. The purpose of J908-2 in a station is to send a signal to the factory tone encoder to disable the transmit tone. In the TS64-MSTII this pin is unused. So, the connection between the station electronics and this pin is severed (which frees up this pin for...) We re-tasked J908-2 as our output for filtered audio from the TS‑64MSTII by connecting the blue wire from the TS‑64MSTII board to it. In other words, a previously unused pin on the TS‑64MSTII board is being used to route the filtered audio out to the station for use as repeat audio.
    3. Cut trace between J904-11 and J951-8. Unfiltered deemphasized (Vol Sq/Hi) audio is fed to the TS64-MSTII via P908-1, but this signal also extends to the output of the System board. The original connection we're removing can be seen as a junction on the LBI-31899 schematic. In order to feed filtered audio from the TS‑64MSTII to the System board, we need to cut the trace that continues this audio signal across to the output.
    4. Add jumper wire between traces of P908-2 and J951-8. Adding this jumper wire passes the filtered audio out of the system board on the original Vol Sq/Hi output pin at J951-8, as shown in Figures 1 and 2, allowing us to connect to Vol Sq/Hi on the backplane to the filtered audio from the TS‑64MSTII, for our repeater controller.


After the above cuts and jumpers are completed the board must be installed in order to have functioning receive audio and station PTT... here's why:

Figure 1 – From LBI31899E, the MASTR II Base Station System Board:

Figure 2 – An enlarged view of the lower left center of the above image:

In closing...

The TS‑64MSTII plugs into P908 on the system board, where the original factory tone board goes, with the component side of the board to the right if viewing the station shelf from the front, where you'd be standing if it were rack-mounted. Below is a shot of the whole shelf of a UHF machine, from an angle that shows where the board goes. The repeater in the photo may not look exactly like yours as ours has the factory metering kit.

Photo 3

The only adjustments are the tone frequency (controlled by six jumpers on the TS‑64 which are connected to a six-position dip switch on the TS‑64MSTII) and the tone encoder level (which is set by the only potentiometer on the board). The board has a timeout timer on it, which should be off / disabled by leaving JP8, JP9 and JP10 un-jumpered (which is how it is shipped from the factory).

A note from WA6ILQ:
Most of my commercial two-way background has been with Motorola equipment, so I asked Nate Duehr WYØX, an acknowledged GE fan to proofread this writeup, since he has used this conversion several times (in fact, Nate provided the photos for this article). In an email to me Nates comment on the encoder tone level pot was:

"I have never had to change/set the tone level from the TS‑64MSTII as shipped from the factory. This modification injects the TX CTCSS tone into the same input circuit to the exciter board as the GE factory CTCSS encoder, and CTCSS level can be set using only the CTCSS LEVEL pot on the exciter board, just like the factory board."

"I've never looked up what the GE exciter is expecting for tone level from the stock board, and I've never measured the output of a batch of TS‑64MSTII's to see if they're all relatively the same from the factory, but never have had to touch the adjustment on the TS‑64 itself yet when setting up this modification, nor have we seen any problems with distortion or any other CTCSS problems as a result. I guess there's always a first time for everything, eventually... but so far, no problems!"

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This page originally posted on Monday 27-Nov-2006

Article text © Copyright 2002 Douglas Sharp K2AD and Repeater-Builder.com 2006
Hand-coded HTML © Copyright 2006 and date of last update by Mike Morris WA6ILQ
Top image is © Copyright Communications Specialists Inc.
LBI images are © Copyright GE and their successors.
Photographs are © Copyright Nate Duehr WYØX 2006 and used with permission.
This page created November 2006 by Mike Morris WA6ILQ from Doug's writeup and Nate's photos with permission from both.

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.