[time-nuts] NIST isolation amplifiers

Bob Camp kb8tq at n1k.org
Wed Nov 26 21:40:12 EST 2014


I very much would not implement that circuit these days. A logic buffer based design beats it on pretty much ever (useful) spec in the book.

> On Nov 26, 2014, at 7:52 AM, Charles Steinmetz <csteinmetz at yandex.com> wrote:
> Bruce wrote:
>> A single 2N2222 or equivalent transistor in a suitable circuit dissipating about 200mW or so can achieve a reverse isolation of 35dB with distortion of around -40dBc (output +13dBm) with a gain of unity, and an output impedance of 50 ohms with a PN floor of around -180dBc/Hz or so.
> For those wondering, I suspect Bruce had in mind something like the attached  (he posted the basic design a few years ago).  I built 8 channels using toroids on FT37-61 cores.  I think the Mini-Circuits T622 should work, but I have not tried it.  The analyses are from my simulation, and the constructed unit performed similarly.  The Miller effect limits fan-out to about 10 for a 10MHz distribution amp.  [Note: the 50 ohm resistors on the outputs represent the external loads, and are not part of the amplifier.]
> Best regards,
> Charles
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