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MSF5000 Digital (CXB) Station Repeater Interfacing Signals By Robert W. Meister WA1MIK

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 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.

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.

• TP9 seems to be the point everybody uses. This is MIC PTT so TX Audio must come in on the MIC Audio line at TP8.
• Pin 4 of the front panel modular Control/MIC jack goes to TP9.
• J802-5 is the MRTI PTT, so TX Audio must come in on the MRTI Audio input.
• TTRC J2900-12 is External PTT that defaults to activate the PTT signal internal to the station, but this can be changed in RSS. This is also available on the DB25 connector on the side of the station at pin 12. Requires TTCB.

TX Voice 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 Voice 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.)

• 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.
• Pin 3 of the front panel modular Control/MIC jack goes to TP8.
• The wire line L1 pair gets transmit audio. This is also present on the DB25 connector pins 6 and 7. Requires TTRC.
• J802-8 is the MRTI Audio Input.

Not all of these audio inputs are suitable for injecting CTCSS or DCS signals. I recommend letting the MSF5000 do that encoding. However, if you absolutely must have your repeater controller encode the CTCSS or DCS signal, one good point to use is jumper JU5 on the SSCB. Remove the two-pin shorting jumper that's there, store it on one of the other two pins, and feed the AC-coupled audio into the center pin. You'll have to adjust the CTCSS or DCS deviation externally. This will inject the CTCSS or DCS signal after the station's deviation EEPot.

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.

• J802-11 is the MRTI Carrier Detect signal and is open-collector.
• U1552-1 is RX1 UNSQ and it goes low when the receiver squelch circuit detects a carrier.
• U1552-7 is RPTR UNSQ and it goes low when the repeater squelch circuit detects a carrier.
• TTRC J2901-11 is the RSTAT signal that goes to +14V with a carrier. Requires TTRC.
• DB25 connector on the side of the station, pin 9. This is programmable via RSS and it can follow any of the MUXBus or High Speed Ring buffer signals. For example, you could program it for RX UNSQ or RX PL DT. Requires TTRC.

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.

• 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.
• J802-10 is the MRTI Received Audio Output. It is de-emphasized and squelched.
• The wire line L2 has de-emphasized and squelched receive audio. This is also present on the DB25 connector pins 2 and 3. Requires TTRC.

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.

• TTRC J2900-8 is RDSTAT and is open-collector. Requires TTRC.
• DB25 connector on the side of the station, pin 9. This is programmable via RSS and it can follow any of the MUXBus or High Speed Ring buffer signals. For example, you could program it for RX UNSQ or RX PL DT. Requires TTRC.

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. Typically the analog grounds are used for audio signals and the logic grounds are used for PTT and COR signals.

• The Analog Ground test point.
• J800-6,7,8,9,10 are all analog grounds.
• J800-21 is a logic ground.
• J801-2,4,6 are all analog grounds.
• J802-7 and either J802-13 (14-pin MRTI connector) or J802-18 (20-pin MRTI connector) are all analog grounds.
• J802-1,3,6,9 are all logic 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 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.