[time-nuts] Phase noise measurement (was - no subject)

dk4xp at arcor.de dk4xp at arcor.de
Sun Aug 22 11:23:10 UTC 2010


 


> > 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







More information about the Time-nuts_lists.febo.com mailing list