noise source question
 

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 ;-)
Thanks
Francesco IZ8DWF

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

noise source question
 

noise source question
 

On 13 Mag, 02:17, RFI-EMI-GUY wrote:
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 ;-)
Thanks
Francesco IZ8DWF

I would think that your biasing of the resistor network would create
some amount of noise which of course would not be attenuated to the same
extent as the semiconductor. But then again it may be negligeable.


well, indeed it would raise the termal noise of the resistor network,
but we are talking about less than 1 mA currents and the noise from
the source will be by far superior. I was more concerned about adding
some DC to the output, I might just try building it, but I was trying
to be sure about possible implications before beeing happy with a
result :-)

Thanks
Francesco IZ8DWF

noise source question