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Better Squelch Action
on a GE MASTR II

By M. Scott Zimmerman and Kevin K. Custer
 


Concept:
Modify the bi-level squelch found in an unmodified GE MASTR II radio for better performance.

Background information:
The performance of the stock GE bi-level (slow / fast) squelch leaves much to be desired. The following modifications will improve the squelch action, and make the GE squelch operation act more like the squelch circuitry in a Motorola MICOR.

For more information on the details behind bi-level squelch, click here.

Modification information:
Bryan Dorbert N3ST gave the suggestion of removing capacitor C630 on the IF/Audio Squelch Board. This capacitor, when removed, will disable the Fast Squelch function.  From the factory, in Station applications, this capacitor is removed.   With this capacitor removed, the "popping" will be reduced when a user has mobile flutter.

(Editors note; This concept will work, however, all it does is disables the fast action; which totally defeats the dual mode squelch.)

A better approach is to lengthen the amount of time the squelch stays open on a marginal signal, but will still allow the squelch to close immediately on a strong signal. This is accomplished by changing the value of capacitor C631. Originally its value is .82 uF. Trial and error has proven that a value of approximately 3.3 uF is a better value for this capacitor.   I would suggest a tantalum or other high quality capacitor be used. Electrolytic types are ok, however they may change value with temperature and this could be a problem in sites that aren't environmentally controlled... you don't want your squelch action to be your repeater building telemetry...

For this mod to work, C630 needs to be in place, so on a mobile don't remove it.
On a Station, you'll need to install this capacitor as it was never present.  C630 is a 4.7 uF, 25 volt tantalum.
C631 can actually be the same value as C630, 4.7 uF, it seems that a 3.3 works fine, but some prefer the slightly larger value.

After changing the value of capacitor C631 (and installing C630 if it is not present), the GE MASTR II's squelch will perform nearly like the famous Motorola MICOR, something that over time has proven to be the best noise squelch circuit for repeater operation, in many folks opinion.

Here's a layout of the System Audio and Squelch board, with both capacitor locations circled.

Here's a partial schematic with both capacitor locations circled. Click on it for a larger view.


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HTML Copyright March 2002, Kevin K. Custer  W3KKC
The information presented on this web site, in and on these conversion pages is © Copyrighted 1995-present by Kevin Custer W3KKC and multiple originating authors.