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MSF5000 Digital (CXB) Station
Repeater Interfacing Signals

By Robert W. Meister WA1MIK
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This is a collection of interface connection points for the analog-plus and digital-capable stations. It's been compiled from other articles and web posts that I've run across. I've checked each of them for reasonableness and made corrections where appropriate. The suggestions in each category are presented in no special order.

For simple repeater controller interfacing, the following signals are usually required:

  1. PTT Input to the station.
  2. TX Audio Input to the station.
  3. COR Output from the station.
  4. RX Audio Output from the station.
  5. Coded Squelch Decoder Output from the station.
  6. Ground.

Note that the Coded Squelch Decoder output implies COR. These are often combined into one signal if both can't be derived. Read more about that below.

Important Notes:

All audio signals should utilize a 10uF 16V electrolytic capacitor in series with any external equipment as the station's audio circuitry is biased at +4.8VDC. Point the positive end towards the MSF5000. Some controllers may already have capacitors in series but always check first.

Logic signals are measured relative to ground.

Most connections are made to points located on the Secure-capable Station Control Board (SSCB) but some will be on the Trunked Tone Remote Control (TTRC) board and are noted as such.

You'll have to use your own imagination on how to secure the wires or if you want to add a connector somewhere.

There are definitely additional places (various IC pins) that you can use to interface your repeater controller. These will vary depending on the particular SSCB in your station. There are at least three different SSCB schematic PDF files on repeater-builder, so you should find one that most closely matches your board, then probe various pins with a voltmeter or oscilloscope to verify the desired signal is present. Attaching to anything on the solder side of the board is quite difficult and not recommended.

The audio signals described here probably are NOT suitable for digital modes, such as D-STAR, AllStar, etc.

Programming Hints:

The station should be programmed as a REPEATER, not a base station. Do NOT put a call sign into the station ID field. Make sure the Transmit Audio/PTT input you choose to use has been coded in the PTT Priority field ('L' for the local mike, 'M' for the MRTI, or 'W' for the wire-line). You'll need a TTRC board and some cables installed to use the wire-line for audio and you will need to set for Full Duplex (4-wire). Also make sure you've got the proper Receiver control Qualifier ('C' for coded, 'S' for squelch, etc). The Repeater Activation and Repeater Hold-in qualifiers can be set to OFF, as you won't be using the station as a stand-alone repeater running without an external controller (that's why you're here now reading this article, isn't it).

There are a few other MSF5000 articles on Repeater-Builder that contain relevant information and may be useful to read at some point:

RSS Programming
MSF5000 Photo Tour, to identify things
MSF5000 Interface Signals

PTT Input:

The various PTT inputs control audio gating for that particular signal. If you ground the PTT side of the SSCB's XMIT switch input, the station will transmit RF but PL/DPL will NOT be encoded. Paging systems often use the XMIT switch terminal for exactly this reason. Depending on where you feed audio into the station, you could use this point as a PTT input.

TX Audio Input:

There are several ways to get audio and repeater controller signals into a digital (CXB) station. The RSS-supported methods of getting TX Audio into the station are:

  1. Local (front panel) Microphone.
  2. Wire Line (4-wire, full-duplex, requires TTCB).
  3. Repeater/Receiver.
  4. MRTI Connector.

Each of these audio sources has a unique PTT input. Audio will only be gated through to the transmitter when the appropriate PTT signal is activated. A PTT Priority field in the code plug specifies which PTT sources can activate the transmitter, and which has priority over the other. The local microphone input is the easiest and most reliable. Audio fed here will be (possibly) pre-emphasized, limited, and filtered. (A field in RSS enables or disables receiver de-emphasis and transmitter pre-emphasis.)

COR Output:

There are two separately adjustable squelch circuits: RPTR and RCVR/RX1. When the station is in local control (ACC DIS) or the PL DIS switch is set, the front panel squelch operates the RCVR/RX1 squelch circuit. There is a slight difference in these two circuits: the receiver squelch will act like the MICOR bi-level squelch where a strong signal will result in a very short squelch tail while a weak signal will have a longer tail. The repeater squelch has a bit more hysteresis and a longer dropout time, to help ride through flutter and noisy reception areas. These are simple noise-activated squelch circuits; they will open with any signal. PL/DPL does not come into play here. Note that some of these signals will require an external pull-up resistor to +5V or +12V, and the best place to put this is inside your repeater controller. Check its input to see what voltage you can safely pull this line up to.

RX Audio Output:

There are two receive audio signals floating around: raw/flat (discriminator) audio, called QUAD Audio, and possibly de-emphasized audio, called RX1 Audio. (A field in RSS enables or disables receiver de-emphasis and transmitter pre-emphasis.) Neither is squelched, however they both go through audio gates as they make their way to the transmitter. If you need gated audio, pick it up after one of these gates. Remember, there are multiple audio paths and gates; make sure the one you use is activated under the right set of conditions.

Coded Squelch Output:

Some repeater controllers have one input for COR and a separate input for PL/DPL Detect. The MSF's microprocessor decodes the PL/DPL and gates the RX1 Audio path when a properly coded signal is received, based on several qualifier fields in RSS. All you can do is utilize this gate control signal. If your external controller has just one COR input and your repeater will be using PL/DPL, you should connect the COR input to this signal.


Don't rely on the chassis mounting screws or a power supply ground. Pick up a ground on the station control board for all the logic and audio connections. Typically the analog grounds are used for audio signals and the logic grounds are used for PTT and COR signals.

Acknowledgements and Credits:

MSF5000, PL, DPL, and a bunch of other terms are trademarks of Motorola, Inc.

Contact Information:

The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.

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This article first posted 28-Aug-2014.

Article text and hand-coded HTML © Copyright 2014 By Robert W. Meister WA1MIK.

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.