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Motorola MSF5000
Interfacing Signals

By Robert W. Meister WA1MIK
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External repeater controllers can be interfaced to MSF5000 stations. Several settings may need to be made via programming to enable specific signals. I am presenting all the information I have found through personal experimentation or examination of the station schematics; I am not recommending or endorsing any specific interface method. My own preference (and experience) for a digital-capable station is to use the signals on the MRTI and TTRC connectors. The audio signals on these connectors are NOT suitable for digital modes, such as D-STAR, AllStar, etc.

On the CXB / RLB (digital-capable) stations, you can tap signals on the Secure-capable Station Control Board (SSCB) test points, MRTI (Microprocessor Radio Telephone Interface) connector, the front panel control jack, and the expansion connector on top of the control tray. The MRTI must be enabled via RSS and 'M' must be in the PTT Priority list in order for the station to respond to signals fed into the MRTI connector. There are two connectors on the Trunked Tone Remote Control board (TTRC) whose signals are available on the station's junction panel if the cabling is present. You can attach wires directly to the TTRC's connectors.

On the CLB (analog) stations, you can tap signals on the Station Control Board (SCB) test points, the front panel control jack, and the expansion connector on top of the control tray. The DC and Tone Remote Control Boards don't provide anything useful except the wire-line interface.

I only have access to a CXB (digital-capable) station. Most of the signal information for that station has been personally measured and confirmed. Information about the CLB (analog) station was obtained from the service manual and has neither been measured nor confirmed. The best way to utilize any of these signals is to measure them with an oscilloscope under actual operating conditions. Remember to add isolation capacitors (10uF, 16V with the positive end pointing towards the MSF5000) on all audio signals if your controller doesn't have them.

General Information:

The MRTI was Motorola's "phone patch" device in the MSF era. Several different models were made by outside companies and sold by Motorola. They have a bunch of internal option jumpers and have to be programmed for the appropriate access codes via its own unique RSS (naturally). These units have their own squelch circuitry and DTMF decoders in them. Most signals are optically isolated and terminated with pull-up resistors. The MRTI is powered by the main 15 volt station power supply. I believe it can only be attached to a digital-capable station.

It is assumed that the person doing the interfacing has service manuals for the station. An enterprising individual can probe around and find lots of signals that may suit his/her needs. Observe normal engineering practices and don't force signals against their will.

Often there are several sources for the same signal. In particular, ground and +13.8VDC can be picked up on test points, terminal strips, and other places. Use whatever is most convenient for you. I personally do not like to modify the existing circuitry or solder wires to IC pins, however sometimes there's no alternative. Ease of maintenance should be considered when attaching directly to components without some means of disconnect.

Most of the receiver audio signals have had PL/DPL filtered out. If you need to use an external PL/DPL decoder, you'll have to use raw, unsquelched discriminator audio, available in several places.

The RSS help file and manual contain a wealth of programming information, useful only for digital-capable stations of course. There are many screens that have insignificant settings in them that you will learn to experiment with as you attempt to interface stuff to the station. Luckily the programming cycle only takes a couple of minutes, but it sure beats having to run to your friend's house to burn a new EPROM, as you'd have to do with an analog station.

NOTE: Throughout these tables, "N.C." stands for "No Connection" and an asterisk next to a signal name indicates the signal is active when low or grounded.

Front Panel Control Jack (all stations):

The local microphone / control jack has several useful signals on it, as described below. "Local" must be specified in the PTT Priority setting on digital-capable stations so the PTT signal will be recognized and enable the audio signal. There may be a similar setting for the analog station's programming. The Speaker Audio output is affected by the front panel volume control, so using this as an output for a repeater controller is not recommended. However, the MIC Audio and PTT inputs can easily be used to accept signals from an external controller. This is a standard 6-position, 6-contact, modular connector. Pin 6 is closest to the volume knob. Note that the CLB (analog) manuals number the pins in reverse, where pin 1 is closest to the volume knob.

Control / Microphone Jack
Pin# Name Function and Notes
1 Logic Ground For PTT and IPCB
2 Audio Ground For MIC and Speaker audio
3 MIC Audio Same as SCM or SSCB test point 8
4 MIC PTT * Same as SCM or SSCB test point 9
5 Speaker Audio [1] Select audio through volume control
6 IPCB Programming input [2]

[1]: The audio amplifier provides about 1/2 watt, enough to drive headphones or a small loudspeaker.
[2]: The IPCB signal is the programming input on digital-capable stations (i.e. the RIB hooks to pin 1 and pin 6). It can also be used to communicate with an analog station.

Wire-line Interface (stations with DC or Tone Remote Control Boards):

Full-duplex audio is available with either DC or tone control boards if the station is configured for four-wire remote control. Audio, which may include control tones (or DC control), enters the station from a remote console on the line 1 pair. You can feed audio into this pair from an external controller through a small audio transformer. You can also inject the proper DC current to key the station, but the audio would have to be AC-coupled. Alternatively, you can feed just audio in and key the station via other means. Audio leaves the station on the line 2 pair. You can retrieve audio from this pair to feed an external controller. The wire-line interface is via four screws on a terminal strip on the junction panel on the side of the station. Jumpers on the remote control boards, or programming, can be configured to use just one line in base station, half-duplex situations.

Expansion Connector (all stations):

This 40-pin connector, J800, is present on analog and digital-capable stations. The metering panels (TLN2418 or TLN2419) plug in here, as can an expansion chassis or a programming cable (for digital-capable stations only). This jack accepts a standard 40-pin IDC (Insulation Displacement Connector) female connector, the same as what you would use on a computer ATAPI / IDE hard drive. Several signals are missing from the analog station but these should not present a problem for most interfacing purposes. The only down-side to using this connector is that you can't attach a metering panel to the station while an interface plug is utilizing it.

Control Tray Expansion Connector J800
Pin# Digital Analog Notes
1 A++ A++ Auxiliary +13.8VDC
2 A++ A++  
3 A++ A++  
4 A++ A++  
5 A++ A++  
6 Audio Ground Audio Ground  
7 Audio Ground Audio Ground  
8 Audio Ground Audio Ground  
9 Audio Ground Audio Ground  
10 Audio Ground Audio Ground  
11 IPCB IPCB Programming line
12 Exp. Reset * Exp. Reset * Reset output to expansion chassis
13 BA0 BA0 MUXBus Address Lines
14 BA1 BA1  
15 BA2 BA2  
16 BA3 BA3  
17 BD0 * BD0 * MUXBus Data Lines
18 BD1 * BD1 *  
19 BD2 * BD2 *  
20 BD3 * BD3 *  
21 Logic Ground Logic Ground  
22 DS * DS * Data Strobe
23 Shut Down * Shut Down * Holds external voltages off
24 Logic Spare Logic Spare  
25 Logic Spare Logic Spare  
26 Audio Spare Logic Spare  
27 Audio Spare Logic Spare  
28 Gen. TX Data Audio Spare  
29 Quad 2 Audio Audio Spare  
30 Diversity Audio Audio Spare  
31 GCC Audio Audio Spare  
32 Select Audio Select Audio Via volume control to metering panel
33 Local Audio Local Audio Audio input; don't use with MIC attached
34 TX Data Audio TX Data Audio Bypasses limiting and pre-emphasis
35 RX2 Audio RX2 Audio  
36 TX Audio TX Audio  
37 Audio Ground Audio Ground  
38 RX1 Audio RX1 Audio  
39 Quad 1 Audio Quad Audio  
40 Audio Ground Audio Ground  

The Wildcard module, which mounts in the expansion chassis that sits on top of the control tray, can be configured to sense or change the four data bits (BD0..BD3) of any of the 16 hex addresses specified by the address lines (BA0..BA3) that float around the control tray. These are known collectively as the MUXBus. These 64 signals are displayed (some of which may be modified) by a diagnostic metering panel or a MUXBus screen in RSS (digital-capable stations only). There are specific interfacing rules, but you could build the appropriate circuitry to make use of these signals if necessary. The analog station has most of these signals available. Wildcards, expansion chasses, and documentation for these are quite rare; expect to pay a premium for them. In other words, find another way to play with these signals.

MUXBus Signals
Addr B3 B2 B1 B0
A RX2 C8 RX2 C4 RX2 C2 RX2 C1

[1]: Bit names with green background colors mean they're read-only status indicators and may not be changed externally on analog (CLB) stations.
[2]: Bit names with aqua background colors mean they're not defined for analog (CLB) stations.

The MUXbus signals are frequently used by wildcard circuitry. You can access the MUXBus in a limited fashion via two pins on the J2 system connector; this is described later in this article. A full description of each MUXBus bit can be found in another document on this web site.

Digital-Capable Stations:

The following table describes the signals present on the SSCB test points:

Digital-Capable SSCB Test Points
TP# Name Function and Notes
1 Select Audio Gated audio to local volume control
2 Logic Ground Ground for all digital logic signals
3 Quad Audio Essentially discriminator audio from RF tray
4 TX Audio Modulation audio to RF tray
5 +9.6V [1] Source of +9.6 volts DC
6 +5V [1] Source of +5 volts DC
7 Analog Ground Ground for all analog signals
8 MIC Audio Local microphone audio (9.6v bias present)
9 MIC PTT * Local microphone PTT (gnd=PTT)
10 Reset * Reset signal source (gnd=RESET)
11 Analog Ground Ground for all analog signals
12 AGC Reference [2] ? ? ?
13 IF Envelope [2] ? ? ?

[1]: TP5 and TP6 are right at the output of the power supply regulators. They can most likely provide several hundred milliamps each.
[2]: TP 12 and TP 13 are present on some SSCBs but are only used on 800/896 MHz stations during alignment.

The following table describes the signals present on the MRTI connector on the SSCB. This connector will have 14 or 20 pins, depending on the version of the SSCB. The pins are industry-standard, 0.025 inch square on 0.100 inch (2.54 mm) centers, single row, the same size as on the Expansion connector or wire-wrap IC sockets. I've used Jameco p/n 103181 single row connector housings with Jameco p/n 100765 female crimp pins for interfacing to all of the internal single row connectors. Pin 1 is towards the front of the control tray.

MRTI Connector J802 on SSCB
14 # 20 # Name Function and Notes [1] Base [2] MRTI [2] Rptr [2]
1 1 Logic Ground        
2 2 PL Strip * Disable transmit PL/DPL No Yes Yes
3 3 Logic Ground        
4 4 Monitor * Disable receive PL/DPL No Yes Yes
5 5 PTT * Transmit No Yes No
6 6 Logic Ground        
7 7 Audio Ground        
8 8 Audio In Audio input to station No Yes No
9 9 Logic Ground        
10 10 Audio Out Audio output from station Yes Yes Yes
11 11 RX Carrier RX carrier indicator (OC) No Yes Yes
12 12 Inhibit MRTI inhibit (OC) ??? ??? ???
  13 N.C.        
14 14 Aux. Indicator Auxiliary indicator (OC) No Yes Yes
  15 N.C.        
  16 A++ Auxiliary +13.8VDC Yes Yes Yes
  17 A++ Auxiliary +13.8VDC Yes Yes Yes
13 18 Audio Ground        
  19 N.C.        
  20 N.C.        

[1]: (OC) indicates Open Collector output from a transistor. You must supply an external pull-up resistor to +5V; I suggest 4.7k, 1/4 watt. The signal is high when active.
[2]: Base is with MRTI and RPTR disabled and neither in the PTT Priority list. MRTI is with MRTI enabled, RPTR disabled, and MRTI in the PTT Priority list. Rptr is with MRTI and RPTR enabled, but without MRTI in the PTT Priority list.

The PTT Priority list, set via RSS, allows for Local, Data, Repeater, Wire-line, and MRTI inputs. The order these are entered determines the priority. Audio from the appropriate source will be gated to the transmitter based on the highest priority PTT input. Local refers to the front panel microphone jack. Data refers to trunking inputs. Repeater is the internal connection between the receiver and transmitter. Wire-line is the two-or four-wire interface on the junction panel that goes through the DC or tone remote control board. MRTI is the MRTI connector on the digital-capable SSCB. Only audio from the source with the highest priority PTT line active will be gated to the transmitter.

Note that most of the signals are not active unless MRTI ENABLED is set via RSS. The station will not respond to PTT requests via the MRTI connector unless the PTT Priority list has "M" (for MRTI) in it. Input audio is only active when MRTI PTT is active.

Additional signal information:

The following table describes the signals available on the TTRC connector J2900. The pins are industry-standard, 0.025 inch square on 0.100 inch (2.54 mm) centers, single row, the same size as on the Expansion connector or wire-wrap IC sockets. Pin 1 is towards the front of the control tray. A cable connects these signals to J2 (System Connector) on the station junction panel.

TTRC Connector J2900 and System Connector J2
Pin# Name Function and Notes [1] J2
1 Audio Ground   17
2 Site Fail-soft * Generates fail-soft tones (in) 18
3 Logic Ground   19
4 TX Inhibit * Inhibits transmitter (in) TX INHB 5
5 Gen. TX Data -   20
6 Gen. TX Data +   21
7 RF Relay Control A+ when transmitter active (out) 22
8 RDSTAT * Carrier with proper PL/DPL (OC) 23
9 Spare Output * Programmable via RSS 9
10 RX Code Detect * Secure data present (OC) 11
11 Fail-soft Indicate * Station is in fail-soft mode (OC) 24
12 External PTT * Causes transmitter to turn on (in) 12
13 RX Inhibit * Inhibits receiver audio output (in) RX INHB 25
14 TX Code Detect * Secure data present (in) 13

[1]: (OC) indicates Open Collector output from a transistor. You must supply an external pull-up resistor to +5V; I suggest 4.7k, 1/4 watt. The signal is high when active.

Additional signal information:

The following table describes the signals available on the TTRC connector J2901. The pins are industry-standard, 0.025 inch square on 0.100 inch (2.54 mm) centers, single row, the same size as on the Expansion connector or wire-wrap IC sockets. Pin 1 is towards the front of the control tray. A cable connects these signals to J3 (Trunking Connector) on the station junction panel.

TTRC Connector J2901 and Trunking Connector J3
Pin# Name Function and Notes J3
1 Logic Ground   17
2 Logic Ground   18,19
3 Analog Ground   20
4 TX Data -   21
5 Trunking Rx Audio out approximately 5VP-P 22
6 Mute * in 23
7 Duplex Enable * in 9
8 Trunking PTT * in 11
9 Control Channel * in, low=control, high=voice channel 24
10 TSTAT Transmitter status (out) always low 12
11 RSTAT Receiver status (out) +14V with carrier 25
12 TX Data +   13

The following table describes the signals on the junction panel's system connector J2 and trunking connector J3. These DB25F connectors obtain their signals from the TTRC J2900, J2901, and the RJ-11 wire-line connectors. See the tables above for functions and notes.

Pin# System Connector
J2 Signal Name
Trunking Connector
J3 Signal Name
1 N.C. N.C.
2 Line 2 + N.C.
3 Line 2 - N.C.
4 N.C. N.C.
5 TX Inhibit * N.C.
6 Line 1 + N.C.
7 Line 1 - N.C.
8 Line 4 + N.C.
9 Spare Output [1] Duplex Enable [2]
10 Line 4 - N.C.
11 Rx Code Detect * Trunked PTT *
12 External PTT * [1] TSTAT
13 TX Code Detect * TX Data +
14 N.C. N.C.
15 Line 3 + N.C.
16 Line 3 - N.C.
17 Audio Ground Logic Ground
18 Site Fail-soft * Logic Ground
19 Logic Ground Logic Ground
20 General TX Data - Analog Ground
21 General TX Data + TX Data -
22 RF Relay Control Trunked RX Audio
24 Fail-soft Indicate * Control Channel *
25 Rx Inhibit * RSTAT

[1]: This pin is programmable via RSS. See below.
[2]: This is undocumented in some manuals.

There are two 6-pin RJ11 jacks on the TTRC analog board. The one closest to the front panel LEDs is J901, and it has L3 and L4 signals. The other jack is J900 and it has L1 and L2 signals. Pin 1 is closest the front panel on both connectors and the signals are described in the table below. Flat wire cables plug into these jacks and the other ends are wired to the DB25F System connector, J2, as shown above. J900 also feeds the L1/L2 terminal strip on the station junction panel. L1 and L3 are inputs; L2 and L4 are outputs. All four are isolated with 600 ohm transformers with 4.7uF capacitors in series.


Another set of signals floating around digital-capable stations is called the High Speed Ring data word. This consists of five bytes of read-only data that can be viewed on the SSCB display and used to activate the "Spare Output" line on the junction panel, which is described shortly. Some bits are used to specify individual conditions, while others are used to specify actual values and as such would not be usable to control the spare output line. All of the combinations are documented in the Digital-Capable Instruction Manual Appendix A. Two bytes are controlled by the SSCB, two bytes are controlled by the TTRC, and one byte is controlled by the Secure module. Most of this data is not terribly useful for interfacing.

High Speed Ring Buffer Word
Byte Signal Name [1] Position[2]
0 RSTAT 10000000
0 RDSTAT 01000000
0 TSTAT 00100000
0 MRTI DVP Mode 00010000
0 Keyword Number # 00000111
1 Coded Takeover 10000000
1 Ring PL Detect 01000000
1 Gen Simulcast RB 00100000
1 Unassigned 00010000
1 PTT Source, etc. # 00001111
2 TX Inhibit 10000000
2 TPTT 01000000
2 Duplex Enable 00100000
2 Control Channel 00010000
2 Fail-soft 00001000
2 WL Key Number # 00000111
3 WL Key Erase 10000000
3 MUTE 01000000
3 Ext Code Detect 00100000
3 Site Fail-soft 00010000
3 DVP Code 1/2 00001000
3 Unassigned 00000100
3 Unassigned 00000010
3 Unassigned 00000001
4 EOM Audio Mute 10000000
4 Pre-RX Code Rel. 01000000
4 Pre-TX Code Rel. 00100000
4 RX EOM Detect 00010000
4 Int. TX CD DT 00001000
4 Int. RX CD DT 00000100
4 Int. ACC DIS 00000010
4 Unassigned 00000001

[1]: A pound sign (#) means these 3 or 4 bits are combined to form a specific value. These fields can not be used to operate the "Spare Output" pin as described below.
[2]: The most significant bit (bit 7) is on the left. Bits are numbered 76543210.

You can program a digital-capable station to activate the "Spare Output line on the TTRC J2900 pin 9 (if a TTRC is present) or the junction panel (J2 pin 9 if a cable is present), when any one of the 64 MUXBus signals is true, or a specific bit is present in the HSR word.

Programming Tricks:

On the Advanced Information screen (page 08 of 10) in the RSS, there is an area at the bottom called "System Connector". The "Spare Output" field is composed of five parts:

To specify the MUXBus signal R1 PL DT (Receiver 1 PL DeTect, Address 03, Bit 2), you would enter "MUXA3B2" in this field.

To specify the HSR signal RDSTAT (Receiver STATus, Address 0, Bit 6), you would enter "HSRA0B6" in this field.

The "Spare Output Pin Active" field can be set to "HIGH" or LOW" depending on which way you want the pin to go when the appropriate signal is active. If set to "LOW", this example would cause J2 pin 9 to go low when receiver 1 detects PL/DPL. There seems to be a bug in some versions of TTRC firmware (for example 5.34) that keeps the Spare Output pin active high regardless of the RSS setting. Version 5.41 apparently fixes this condition, and it has been verified. It may work fine with other versions or other MUXBus bits.

You can similarly program the External PTT input (J2 pin 12) to perform some other function besides causing the station to transmit. For example, to disable transmit PL/DPL when this pin is grounded (TX PL DS), enter "MUXA2B3" in the appropriate field. Note that this action, like the PL Strip input on the MRTI connector, immediately stops the PL/DPL generation with NO reverse-burst or turn-off code, at least on stations with the latest firmware when keyed up via the MRTI PTT input (even though the printed MUXBus documentation says it does generate RB/TOC).

This page, extracted from the RSS Programming manual, is the source of this information.

Analog Stations:

The following table describes the signals present on the SCM test points:

Analog SCM Test Points
TP# Name Function and Notes
1 Select Audio Audio to local volume control
2 Line Audio Audio to remote control board
3 RX Audio Discriminator audio from RF tray
4 TX Audio Modulation audio to RF tray
5 RX1 Audio Level-controlled de-emphasized RX audio
6 Rptr. Un-squelched Repeater un-squelched = +2.9VDC
7 RX1 Un-squelched Receiver un-squelched = +2.9VDC
8 MIC Audio Local microphone audio (bias present)
9 MIC PTT Local microphone PTT (gnd=PTT)
10 Test Indicator +2.9VDC when TEST LED turned on
11 DC/TRC Select Remote Control type (gnd=DC, high=tone)
12 +5 Volts May be marked +5V
13 Logic Ground May be marked L.G.
14 +9.6 Volts May be marked +9.6V
15 Audio Ground May be marked A.G.
16 Audio Ground May be marked A.G.
17 IF Envelope Only present on 896 MHz stations
18 AGC Reference Only present on 896 MHz stations

Other Interfacing Schemes:

Some of the logic signals in the analog station run from 0 to +2.9VDC which is technically not TTL-compatible. Measure the signal with an oscilloscope to see what it looks like before using it for interface applications, to prevent surprises when you're done.

All audio connections to the MSF5000 internal control board should be AC-coupled. Several junction points are biased at +4.8VDC and any low impedance load attached to the circuitry can cause problems. A 1uF capacitor would be adequate for normal audio; something larger might be necessary for external PL/DPL signals.

The following data was extracted from an article by Jim WD5IYT:

Signal Name Analog Station
V+ +9.6 Volt Test Point
Ground Ground Test Point
Discriminator J800 pin 39
Carrier Sense Test Point 7
TX Audio U838 pin 6
PTT U813 pin 5 (XMIT switch)

Another interfacing scheme for an analog station is shown below. It doesn't deal with PL decode, however; that would have to be obtained from the MUXBus using a wildcard or other external circuitry:

Signal Name Analog Station
Ground Logic Ground
RX Audio U832 pin 15 or U835 pin 1
RX Unsquelched Test Point 7
TX Audio Test Point 8 (local MIC)
PTT Test Point 9 (local PTT)

The following signals are used by Zetron according to the instruction manual for their model 38A Repeater Tone Panel. To use these signals, the ACC DIS switch on the control tray's front panel must be set. The control tray's front panel SQUELCH control will set the carrier squelch threshold.

Signal Name Analog Station Digital-Capable Station
Ground [1] J800 pins 7 & 8 Test Point 2
+12 Volts DC [1] J800 pins 1 & 2 R8121 side towards center of SSCB
Discriminator Test Point 3 Test Point 3
Carrier Sense Test Point 6 U1552 pin 1 +8V no signal, 0V signal
TX Audio U834 pin 13 [2] U814 pin 2 [2]
PL/DPL Audio Wiper of R889 (IDC) [2] U831 pin 3 [2]
PTT J801 pin 14 [3] SW800 front-most lead (XMIT)

[1]: Ground and +12VDC can also be found on TB601, the +15V terminal strip on the power supply that feeds the power amplifier.
[2]: These audio signals pass through a 33k resistor to the indicated point.
[3]: PTT can be applied to the same XMIT lead of the front panel switch as on the digital-capable station. See the following paragraph for an explanation.

The PTT connection point for the analog stations, specified by Zetron, is the PA KEY signal going to the RF tray. It activates the transmitter only; it does not actually "key" the entire station like PTT does. The RF tray generates power without the SCM worrying about timeouts. It also requires the user to supply all transmit audio and PL/DPL.

The following simple interface information for a digital-capable station came from Jason WA1NH. Note that a TTRC and its various cables are required for this scheme to work; most stations have them.

I am curious as to who stated that hooking an external controller to an MSF5000 was not worth the effort. It allows remote knockdown and linking on a remote base connector to the controller. I was able to do it with little effort.

Here is a snapshot of what to do to accomplish it the easy way. In RSS, disable repeater and leave callsign space empty. Set PTT Priority to "L" (Local) then "W" (Wireline). Set timeout timer to off. Next, remove the two screws that hold J2 to the station junction panel on the case of the repeater and push it to the inside of the cabinet. This allows the controller to be placed inside the repeater and away from wandering hands.

Interface the following pins on J2 to your external controller: (please note that I used 1:1 audio transformers on the audio lines to isolate both sides from ground.) [ Editor's Note: Additional transformers are NOT necessary since the station already provides its own to isolate all audio going to and from J2. Remember to set the appropriate EEPots for Line 1 and Line 2 levels. ]

That was Easy!!!!

Now you have to find a controller that has a remote base port for linking (IRLP, EchoLink, RF) and a control receiver audio input. Remember to set "ID over remote base port" to OFF for EchoLink and IRLP.

Taming the Internal Controller:

People often ask: "Why can't I just remove or bypass the internal controller and use that super-duper powerful Binford 6100 repeater controller instead?"

You can't just remove the SSCB or SCM; it's an integral part of the station and it does a lot more than you may realize. The MSF5000 is a synthesized programmable full-duplex station. The internal controller stores and utilizes the code plug, which deals with programming parameters such as transmit and receive frequencies and PL/DPL. It generated the CW ID, which can be set to commercial or amateur standards (digital-capable stations only; the CLB stations were hard-coded to 15 minute intervals). It has timeout timers for all PTT sources. It runs diagnostics on the various components and audio paths. It operates the synthesizers in the RF tray. It provides two separate squelch circuits. It handles transmit audio processing. In short, it's an integral part of the station and some sections of the controller are required to enable the station to transmit and receive.

You can use as many of the features as you want, or none at all. For example, my digital-capable UHF repeater uses an inexpensive external controller. I configured the MSF5000 as a base station with no CW ID and all the timeout values set to zero (this disables them). I programmed the transmit and receive PL tones into the SSCB. The interface between the station and the controller is seven wires attached to the MRTI and TTRC connectors, just the necessary signals to make a repeater: receive audio, receiver active (RX1 ACT), PL and carrier detected (RDSTAT), monitor (to disable PL receive), transmit audio, PTT, and ground. I let the MSF5000 do what it's best at, while letting the external controller handle CW ID, timeouts, voice messages, and DTMF decoding for control functions.

I have another system configured as a stand-alone repeater. I set the input timeout to 180 seconds, enabled the CW ID with a zero delay time and an eight minute interval, and used a 12 second hang time. This way, the CW ID is heard during the hang time, while the transmit PL is still active (Normally the CW ID is sent without PL; some people like it that way, others don't.) I can attach an external DTMF decoder to one of the receive audio lines, and use it to control the transmitter via the TX INHB input line. I could attach another audio source to the MSF5000, such as a voice module on an external controller, and have messages and announcements.

Granted, the MSF5000 is not the most amateur-friendly station in the world, but it was designed before many of the sophisticated multi-port, linking, do-everything chatter-boxes came on the market. I go for simplicity and reliability rather than all the bells and whistles (and burps, cricket chirps, twangs, laser gun zaps, etc.) that seem to proliferate some frequencies these days.

There are things the MSF5000 just can not do. For example, the stock internal controller (SSCB or SCM) can't encode or decode multiple PL/DPL tones on the same channel; you'd need an external community tone panel to do that, such as provided by Zetron, or a Multi-Coded Squelch (MCS) board in an expansion chassis. You can program several channels and/or modes into the station and switch them externally, but you're pretty much stuck using the existing remote control schemes (tone or DC) to do so. You can't change channels or modes while the station is transmitting. If your application requires changing the PL or DPL codes on-the-fly, you'd need to utilize an external encoder or decoder and connect it into the control board at the proper spot.

You can "tame the beast" and turn off every internal controller feature, leaving you with a radio that functions like a programmable MICOR, to which you can connect your own fancy external equipment. You can also "go with the flow" and let the MSF5000 do what it's best at: a great receiver, a continuous-duty transmitter, PL/DPL encode and decode, a robust power supply, and audio processing. Then add whatever else is necessary for legal control requirements. You'll end up with a stable workhorse that will give years of excellent service.

Acknowledgements and Credits:

All MSF5000 technical information came from Motorola's official documentation:

Jim WD5IYT also has an MSF5000 interfacing article. Information extracted from that was done so with his permission.

A Zetron Model 38A Repeater Tone Panel Instruction Manual, Part No. 025-9043Y, was used for some information. Written permission was obtained to use the manual as source material. Zetron has not endorsed the solution described in this overall article.

Of course, thanks always go to Mike Morris WA6ILQ of the Repeater-Builder staff for converting this article to HTML. There's a lot more work involved in that process than you'd think.

MSF5000, DPL, PL, MRTI, MICOR, and a whole lot of other terms are trademarks of Motorola, Inc. Other trademarked names including EchoLink and IRLP) are the property of their respective owners.

Contact Information:

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

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This article first posted April 2006.

Article layout and text Copyright © 2006 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.