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May 12th 08, 11:10 PM posted to rec.radio.amateur.homebrew

Doug White Doug White is offline

Doug White is offline

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First recorded activity by RadioBanter: Oct 2007

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noise source question

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In article , wrote:
Hello,

I'm willing to make a noise source from an UHF transistor (B-E
junction reverse polarized like a zener) and I was wondering if it's
ok to use the output attenuator as part of the resistor network for
the DC bias of the transistor (or zener). I'd probably look at the
arrl handbook if I had it ;-)

Depending on how you do it, the noise can degrade over time. You are
better off using a diode. My recollection is that a true zener (around
3V) works best. I worked on an HP instrument that was originally
designed with a reverse biased transistor as a noise source. The noise
spectrum degraded over time and caused a lot of warranty returns. I
replaced it with a diode, and all was well. This was 30 years ago, so I
don't remember the details. This was for a low frequency noise source,
and things may behave differently for an RF source.

Doug White

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