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MSF5000 Analog (CLB) Station Repeater Interfacing Signals By Robert W. Meister WA1MIK

This is a collection of interface connection points for the analog 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 Voice 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. All connections are made to points located on the Station Control Board (SCB). You'll have to use your own imagination on how to secure the wires or if you want to add a connector somewhere.

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, and In-Cabinet Repeat should be disabled. Do NOT put a call sign into the code plug EPROM. Make sure the audio/PTT input you choose to use has been coded in the PTT Priority field ('L' for the local mike or 'W' for the wire-line). If you're using the wire-line, you will want it 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 control qualifier 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:

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

PTT Input:

Ground this line to cause the transmitter to key up. If you ground the 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. If you plan to have your external controller also encode PL/DPL, you could use this input.

• TP9 seems to be the point everybody uses. This is MIC PTT so TX Audio must come in on the MIC Audio line.
• U813-5 is the same as the XMIT switch mentioned above.
• J801-14 is the PA KEY signal going to the RF Tray. It just causes the station to transmit RF only. The front panel PA KEY LED is attached to this line and it indicates that the RF Tray has been told to transmit. This bypasses all the logic on the control board.

TX Voice Audio Input:

There are several ways to get audio and repeater controller signals into an analog (CLB) station. The methods, which are supported by the code plug and programmer, of getting TX Voice Audio into the station are:

1. Local (front panel) Microphone.
2. Wire Line (4-wire, full-duplex, tone or DC).
3. Repeater/Receiver.

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 pre-emphasized, limited, and filtered.

• TP8 is MIC Audio. This goes along with TP9: MIC PTT. There will be +9VDC present on this line and it is a low impedance (about 600 ohm) input.
• U834-13 is the TX Audio Summing Amp input, un-gated.
• U838-6 is the TX Preamp/Limiter input.
• U832-15 is TX Audio after all source gating.
• J800-33 is the Local Audio Input, same as TP8.

Not all of these audio inputs are suitable for injecting CTCSS or DCS signals. I recommend letting the MSF5000 do that encoding.

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.

• TP7 is the RX1 UNSQ signal that rises to +2.9V (or higher) when a carrier is detected.
• TP6 is the RPTR UNSQ signal that rises to +2.9V (or higher) when a carrier is detected for repeater use.

RX Audio Output:

There are two receive audio signals floating around: raw/flat (discriminator) audio, called QUAD Audio, and de-emphasized audio, called RX1 Audio. 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.

• TP3 is raw (flat) discriminator audio coming from the RF Tray. You would need separate de-emphasis, PL filtering, and possible squelch/muting circuitry following this.
• TP5 is de-emphasized, high-pass filtered, but un-squelched RX1 audio.
• U832-14 is gated RX1 Audio.
• J800-39 is the same as TP3, also called QUAD Audio.
• U835-1 is the same as TP3, also called QUAD Audio.
• J800-38 is the same as TP5, also called RX1 Audio.

Coded Squelch Output:

Some controllers have an 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. 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 and ignore the station's COR (squelch) outputs at TP6 or TP7.

• U829-14 rises to +2.9V (or higher) when the proper PL or DPL code is received.
• U829-15 is a buffered version of U829-14. This pin rises to +9V (or higher) when the correct PL/DPL is gated through the station.

Ground:

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.

• The Logic Ground test point can be used as an analog ground.
• J800-6,7,8,9,10 are all analog grounds.

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 11-Nov-2011.

Article text and hand-coded HTML © Copyright 2011 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.