It's probably a lot more common to express the noise referred back to
the input, but if it's output noise you want, that's fine too. You'd
want to either use a drain load that's much higher resistance than the
output (drain) resistance of the FET at that bias--or else account for
the shorting effect of the load.

Often the noise is so low you would be served well by amplifying by
100 or 1000 so your "meter" has enough to measure accurately.

If I were doing it, my "meter" would be an FFT-based spectrum
analyzer, which would be able to read the amplitude directly in
V/rtHz; then I'd just divide by the gain, if I'd used an amplifier.
(I have a very low noise amplifier I use for just such measurements,
so the amplifier doesn't contribute a lot to the measurement, but even
then, it may be necessary to subtract out the amplifier's noise
contribution.) If you really need to know it at 10Hz, you probably
should not use a bandwidth much more than a couple of Hz. An
FFT-based analyzer (or possibly other spectrum analyzer, or even a
wave meter/analyzer) makes that fairly easy. Not sure this will help
in your particular situation.

Cheers,
Tom

wrote in message . ..
I need to measure the "equivalent noise voltage", in units of
nV/square root( hz) of a JFETs drain-source at a given Vds & Ids and
F=10 hz. How do I do that? What's throwing me is the F=10 Hz. What do
I do with that? I thought to take the measurement, I would bias the
FET to the required Vds and Ids and measure the voltage across the
drain - source with an RMS meter. Then divide that by the sqrt of the
bandwidth of the RMS meter. I've Googled, but didn't find anything to
straighten me out. Any help?