Mastr II Base to Repeater conversion

Preliminary - 15 June 2003

For a Mastr II Base you need to modify the system board if it was using CG previously or was a multi-channel unit. Basically you remove all of the cards except the 10v regulator, modify the 10v regulator card if necessary and remove or add a few jumpers to the system board. As far as dealing with the amplifier T/R relay follow the instructions on the Repeater Builders site to deal with the T/R relay. Connect your controller.

1) Tune up radio

2) Remove all cards from the shelf except the following

10v Regulator card

3) Modify 10v Regulator card if necessary

 Check jumpers 1,2,3 and 4: 

Ensure that 1 is connected to 2  and 1 is connected to 3

4) Cut the following System Board jumpers if present

H41-H42 (RX Mute/CG Out)

H68-H69 (TX CG Disable)

H72-H73 (Voting) - was present in my base

5) Make sure the following jumpers are present

J933 Pin 4 to pin 8 (F1 for TX) on Exciter

H47-H48 (F1 for RX) on System Board

6) Deal with T/R relay

7) Hook up a controller

Controller Mastr II Notes   Mastr II Backplane location

 TX Audio High

 Trans Audio Hi

Inject the transmit audio into the microphone input of the radio. Be aware that this input has a +10V bias applied, which is intended to power the microphone preamp. You might need to insert a DC blocking capacitor here, probably an electrolytic in the range of 1-10F (watch the polarity!). If you are planning to use a local microphone on the control head, you might want to insert a resistor in series with the controller's audio output to prevent the controller from loading down the microphone's output. 5K would be a good value to start with.   


 TX Audio Low

 Trans Audio Lo 

Audio ground  



 Local PTT

Ground to transmit


 RX Audio High

 Volume / Sq Hi

This source of receiver audio must be de-emphasized. The de-emphasis filter should have a -6dB/octave slope for proper frequency response. If the receiver audio is not de-emphasized, the repeater will sound really "tinny". Many controllers have built-in de-emphasis filters. If yours does not, you can make your own with a 15K resistor and a .22F capacitor. Wire one side of the 15K resistor to the volume/squelch hi signal, and the other side to one side of the .22F capacitor. Ground the other leg of the capacitor. Take the receiver audio from the capacitor-resistor junction.  


 RX Audio Low 

 Volume / Sq Low

Audio ground




Be very careful of the CAS signal, it cannot source much current at all. You can convert the CAS signal to open-collector by using a 2N2222, with the emitter grounded and the base connected to the CAS signal through a 10K resistor. The collector of the 2N2222 will be pulled to ground when the squelch is open (signal being received).  


 CTCSS Decode

 CG Decoder Output 






 10v  10v  TB1201-9



The System Board



Updated: 8 May 2003