[R-390] Q IF And Audio Module Tube Optimizing

[Flowertime01 at wmconnect.com]

Tisha,

A real great point on trying to get a sense of the band pass shape of the 
filters in a (your) receiver. Back when we never worried, as a filter passed 
or did not pass a signal.

But today we know about the insides reducing to gooey crud. This can cause 
all kinds of dead spots within a band pass.

Yes, we should add a section on doing a simple (not sweep generator) test 
that results in a chart / graph of the band pass of each mechanical filter in 
the IF deck.

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You wrote,

It is disconcerting to me to be trying to dial into a signal and when I
rotate the bandwidth switch I hit spots where the signal just completely
disappears. I have some examples were it was not just related to the S/N
ratio and a wider bandwidth resulting in an AGC action that drives the
desired signal down through the floor.
-----
Yes as we change band width, other signal gets into the mix and into the 
AGC. This adds AGC reduction, this drops RF gain, this drops our wanted signal 
into the noise.

I am thinking that at some signal levels we rattle gooey crud and thus 
loose the signal or have dead spots. We are lucky the crud is not hanging the 
filter in a completely dead inoperative state that passes no signal at all.

I also think the crud can hang on a filter wafer and thus change its 
resonance. To our ears it is as if audio notches are being formed.

We just always peaked the trim caps on the IF for maximum gain on any 
filter. The real intent was to match the gains of the filters together. But the 
procedure is still to use a signal generator of clean single source signal. 
This is not the real world performance of what happens in the filters and AGC 
action. 

You are right. The trimmer caps can be used to better match and thus 
improve the apparent in your ear performance of the receiver. I just do not have a 
procedure to do a comparison of the filters.

OK Fellows how do we do this with the AN/URM 25 and volt meter? How do we 
do this with a nice sweep generator and scope? What do we find as a base line?

Roger AI4NI</HTML>