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 that right?

Many thanks,
John.


Yikes!

100dB?

I suggest you use a modern mixer IC like Analog Devices AD8343. You can
achieve -50 to -57dB harmonics rejection with these mixers and each mixer
presents a gain of 7dB as well.


Dan / M0DFI