[time-nuts] NIST isolation amplifiers

Bob Camp kb8tq at n1k.org
Tue Nov 25 20:02:56 EST 2014


I’ve built that one as well. It’s a bit easier with +/- supplies. 

It has the same “you need a good layout” issues as any of the other versions. It’s got a bit higher input impedance than the others so it’s better choice for > 4 outputs. 


> On Nov 25, 2014, at 6:53 PM, Gerhard Hoffmann <dk4xp at arcor.de> wrote:
> 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
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