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  Interfacing an ACC RC-850
Repeater Controller to an
MSF5000 CXB Station

Originally titled:
Specifications Covering the Line-up and
Installation of the VHF Motorola MSF5000
(possibly published by ACC itself)
Transcribed by Robert W. Meister WA1MIK
(with some corrections and improvements)
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Disclaimer from WA1MIK:

The original author and source are unknown. This document was something I found on the web and printed in 2002 and stuffed into a binder. It is incomplete and there are lots of omissions and errors. I merely transcribed it. You get what you pay for. See the "Contacting Us" page on the Repeater-Builder main index page if you can offer improvements or corrections.


This document summarizes the changes in configuration as well as the interface specifications for a VHF Motorola MSF5000 in order to be used with the ACC RC-850 repeater controller.


The equipment covered by this specification is as follows.

Software Configuration:

"SoftPot" settings for initial installation were changed as follows.

SoftPotSignal Being AdjustedOriginalModified
0Coded (Decrypted) RX Level 5000
1Flutter Fighter Level (896 MHz only) 1000
2Repeater Squelch Level 7878
3Receiver Squelch Level 7373
4Maximum Deviation Level 8282
5Receiver (Repeater) Level 9999
6Coded Deviation Level 8900
7Transmit Line Audio Level 4100
8Status Tone Level 5000
9High End Equalization Level 0000
ALow End Equalization Level 0000
BTrunking Data Deviation Level 0000
CLine 2 Output Level 5000
DLine 4 Output Level 0000
ECoarse Line Output Level 0200

[The following paragraph added by WA1MIK:]

You must enable the MRTI interface port on page 6 of the Advanced Information settings. You must also add "M" (MRTI) to the PTT Priority field list and set the MRTI TOT (Time-Out-Timer) field to 000 for the mode being used by the repeater. There are other configuration parameters that also must be set when using an external repeater controller. All of these settings are changed using the Radio Service Software (RSS).

Hardware changes from the original configuration (as purchased)

Secure Capable Station Control Board (SSCB):

Trunked Tone Remote Control Board (TTRC):

Secure Module:

Interface Specifications:

Upon researching the various options for interfacing the control and audio lines from the RC-850 to the MSF5000, it was determined that using the MRTI interface connector on the MSF5000 was the most effective option. It was also decided to combine all of the audio and control lines to and from the MSF5000 into a female DE-9 connector to be mounted to the chassis. This was done in order to assist in the ease of installation and removal of the MSF5000 or the RC-850.

The pinout of the MRTI (J802) connector is as follows. Click on the image for a larger view.


Note that this connector can have either 20 pins (older board) or 14 pins (newer board), but the usage of the first 12 pins is the same. The pins used on this connector are as follows.

PinSignal NameUse or Function
1Logic Ground Ground connection used as reference for logic connections.
2MRTI PL Strip* Active low input. Tied to Autopatch Offhook output from RC-850. Allows DPL transmitted during normal operation to be turned off during an autopatch call to facilitate selective monitoring.
5MRTI PTT* Active low input. Used as PTT input from RC-850 to key transmitter.
7Audio Ground Ground connection used as reference for audio connections.
8In MRTI Audio Audio in from RC-850 to be transmitted.
10Out MRTI Audio Audio out to RC-850 from receiver.

The pinouts of the TTRC connectors (J2900 and J2901) are as follows. Click on the image for a larger view.


Most of the pins used for the interface to the RC-850 are available from the MRTI connector (see above). However, one pin that is required but is not available on that connector is some sort of Carrier On Receive (COR) signal.

That signal is available as either active low or active high as required. The pins involved are:

The only other signal required is an external keying signal (/PA KEY) for the power amplifier. This signal is active low and is available from the RF Tray Interconnect Board on either J502A, pin 6 or J596A, pin 4 as desired. Ground, if required, is available at J502, pin 5 or J596A, pin 3.

[The following paragraph added by WA1MIK:]

I don't know why they need the external keying signal described in the paragraph above. This signal isn't brought out to the DE-9 connector or the RC-850 controller via the interface cable below. They DO seem to want /AC FAIL, an active low signal that comes from the power supply. This IS available on the RF Tray Interconnect Board at J701A, pin 4 as documented below.

DE-9 Connector Pin Specifications:

The pinout of the DE-9 connector added to the MSF5000 chassis for interfacing to the RC-850 is as follows:

DE-9MSF5000RC-850 Description
1J802, 7DA-15, 2 (AGND)Audio Ground
2J802, 8DA-15, 1 (J10, 10)Audio From RC-850
3J802, 10DA-15, 9 (J10, 2)Audio To RC-850
4J2900, 8DA-15, 8 (DGND)Logic Ground
5J2900, 3DA-15, 7 (J6, 17)/COS
6J701A, 4(J6, 14) (Digital Input)/AC Fail
7J802, 1DA-15, 8 (DGND)Logic Ground
8J802, 5DA-15, 5 (J6, 7)/PTT
9J802, 2(J7, 8) (Digital Output)/DPL Disable

RC-850-MSF5000 Interface Cable Specifications:

The cable below was constructed to interface the MSF5000 to the RC-850. A resistor divider network was used to reduce the audio to the RC-850 from about 6.4 Vpp to 1 Vpp (at 1kHz).


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This article transcribed 03-Dec-2011.

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.