On Wed, 28 Jun 2006 22:10:46 +0100, john wilkinson
wrote:

Thank you all for being pacient with me and my stupid questions.

Another thought has just raised its head.

I have 2 IF amps. 1ts with approx 20dB gain, second with 100dB gain.
The first IF has a XTAL filter at 45MHz.
The second has the collins mech filter at the beginnig, then 100dB gain,
straight into a diode detector.

I think I need some form of additional filtering at the output of the
second IF, before the detector, to reduce the noise introduced by the
100dB amp, else it don't work. Except for strong signals.

is this FM or AM/SSB/CW?

IF FM the 100db amp will be limiting by time the input is around
10uV.

IF AM/SSB/CW you should be seeing AGC voltage developed
by time the input is 10uV (50 at the extreme max).

I suspect the 20db 1st IF is not happy. FYI those 45mhz filters
are fairly wide (usualy 15khz or more). So any selectivity
is developed in the latter stages (your MF). However the
problem is you can easily be overloaded by strong close
signals by then.

Is that right?

Depends on the answer to the question.

Many thanks,
John.

Allison