[time-nuts] NIST isolation amplifiers

[Gerhard Hoffmann]

Am 25.11.2014 um 20:34 schrieb Charles Steinmetz:
> A couple of people were asking about NIST isolation amplifiers 
> recently.  I'm attaching circuit diagrams of the 5-10 MHz amp from 
> 1997 and the 1-200 MHz amp from 1990.  I think Bruce has the papers 
> linked at his ko4bb.com pages.
I have built _this_ version of the NIST preamp 6 or seven years ago. It 
is quite ok and feeds the
signal generators, counters, SAs and VNA  in my lab without issues. 
There is >1 successor that
corrects the awful S11 and has no output transformer but it still awaits 
characterisation. Maybe
over the holiday season to come.

Noise on the base voltage string is attenuated by transistor beta in the 
cascode, so there is not too
much to gain here. The next 2 versions use even more current to support 
13 dBm without transformer,
they run pretty hot ( 2 BFG31 chains/channel).

< http://www.hoffmann-hochfrequenz.de/downloads/downloads.html >

regards, Gerhard