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 that right?

Many thanks,
John.
I put a ceramic filter after my last AD603 amp, and bingo!!! I get quite
good reception.

I think the 2 off AD603 with no output filtering was swamping the diode
detector with the noise floor level.

However, the detector is buffered from the filter through an emitter
follower, and guess what it oscillates at 170MHz.

How do I cure this?

Has anyone seen an emitter follower oscillating before?