EMRFD Message Archive 216

Message Date From Subject
216 2006-11-26 18:35:20 Mike Czuhajewski Microphonic mixer chips?
> Mixer is a MC1496 which in my opinion has less microphonics than
some NE602
> and SA612 mixers.

Fascinating. I had never heard that one before. Is there any data to
back that up? I would expect microphonics to be generated by something
other than ICs, although I suppose anything is possible. Perhaps other
things in the circuits were causing the microphonics? Was the exact
same test bed used to make a comparison? (Not just an identical
circuit built from the same schematic, but a single collection of
components with one mixer substituted for the other and results
compared. That would eliminate all possible variables.)
217 2006-11-26 19:25:55 Loren Moline WA7S... Re: Microphonic mixer chips?

I believe the microphonics or sound in receiver when it is moved is caused
by some feedback within the mixer circuit. Sometimes there is more of the
local oscillator component in the output of the mixer than others maybe
attributed to the balance of the mixer and rejection of the oscillator.

I believe even though the output is audio and filterted that some of the
oscillator signal is not fully rejected which can cause problems in the
following audio stage.

I have built a direct conversion receiver from Ramsey and it does not
perform as well as mine. And it does use the more modern NE602 mixer.


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