[Milsurplus] scr-287 integration question

[W7QHO at aol.com]

In a message dated 8/19/06 8:58:14 PM, scr287 at sbcglobal.net writes:


> The '375 mutes the '348 by opening a set of
> normally closed contacts, this takes screen voltage
> off the the IF and one of the RF amps in the receiver.
> 
> Mine does this, but the receiver still operates well enough
> to hear the transmitter. Even with the antenna leads
> disconnected from the receiver. It is not grid rectification
> or audio coming in the power socket, as it is tunable.
> 
> Just wondering if this is a design feature to provide side tone,
> or do I have some other issue?
> 
Jack,

Interesting, have run a BC-348 with my BC-375, but muted by breaking the 
ground end of the RF gain control, thus completely cutting off both RF and the 
first and second IF amps.   Experience no transmitter signal feed through using 
this method.

Can see how merely cutting off the SG voltage might not be enough for 
complete muting.   The HF osc/mixer is still running as are the first RF and the 
third IF stages.   Removing the SG voltage alone does not reduce the gain of the 
affected stages completely to zero, the SGs have to be driven somewhat negative 
to do this. 

Don't know whether or not this might have been a design choice to provide a 
side tone (or for some other reason). 

The Navy TCS receivers are also muted by removing SG voltage to the RF and 
first IF   and also the mixer stage.   Have noticed no feed through with these 
sets, so maybe disabling the mixer makes the difference.   Note, though, that 
the TCS transmitter puts out much less power than the BC-375.

Good luck with the project.

Dennis D. W7QHO
Glendale, CA