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Technical Tips from Mark W. Persons

Marti CR-10 Receiver Modification

This modification is for anyone who has a Marti CR-10 Remote Pickup Receiver in an environment where people are working and/or where there are live microphones nearby.  The squelch relay in these receivers can be very mechanically noisy when it engages and disengages.  Part of the problem is that the metal receiver cabinet tends to amplify the sound, much to the dismay of those in the same room.  A chattering relay can be most distracting. 

Shown in the photograph is the Marti 800-219 Power Supply/Squelch Board, which normally has a relay plugged into a 16-pin DIP socket.  In its place is a transistor with two resistors.  This modification makes the receiver completely silent.  The downside is that the original relay can also be used to turn a transmitter on if this receiver is part of a repeater system.  This is not normally the case when the receiver is used in a radio studio environment.  

Here is the circuit.  It is a 2N7000 N-Channel Field Effect transistor with two 10,000 ohm resistors attached.  The lead numbers indicate which socket connections it is plugged into. 

This circuit worked quite well for the client.  Perhaps a better mechanical solution would have been to solder the transistor and resistors to a 16-pin header plug for easy insertion in the original relay socket.  I suspect the modification will also work in Marti AR-10, BR-10, and DR-10 Receivers as well.

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   ham W0MH      

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