> > NXP BF862, available from digi-key.
> >
> Don't these devices have relatively high flicker noise?
1/f corner is well below 100 Hz. Look at the noise voltage plots of
that audio guy I cited.
My results for the BF862 were the same shape, absolutely somewhat worse
in amplitude because I wanted a differential input and less FETs in parallel.
Most of my BF862 had abt. 12 mA IDss, btw.
> The input capacitance is relatively noncritical in this application
> (phase noise measurement) since it is shunted by the much larger output
> capacitance of the low pass filter at the mixer IF port.
The 300 pF Cin of a single IF3602 could seriously detune the input low pass
and the 200 pF feedback capacitance in a stage with substantial voltage
gain would destroy the bandwidth unless cascoding is provided.
I think, I'll test some Analog Devices ADA9848-2 in parallel. It's hard to beat
that combination of noise, 1/f, bandwidth, offset stability and price.
Such a preamp can be used as an add-on to a scope or FFT-Analyzer, too,
to characterize power supplies, references or oscillator bias circuits.
It's fun to enter 60 dB probe gain into a scope channel menu
and still see usable traces with uV/div scale factors.
( with a low pass, of course)
There are noise nuts, too! ;-)
Gerhard
> > One heroic effort for audio is here:
> > http://www.diy-audio-engineering.org/index.php?board=2.0 HPS5.1
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