[time-nuts] high rev isolation amps

Richard (Rick) Karlquist richard at karlquist.com
Sat Mar 26 19:14:07 EDT 2016


Nothing has come to my attention in the last
35 years that is superior for buffer amplifiers
to the simple cascade of grounded base transistors
as described by numerous NBS/NIST papers.
The chain usually starts with a common emitter
(with emitter degeneration resistor), which
is an even older NBS classic.

I realize you asked for an OTS connectorized
version.  Unfortunately, I have never seen
one of these offered in said 35 years.
When I worked for Agilent, there was an IC
version made by a captive fab.  It was
never spun off as a commericial part via
the semiconductor division (which is now
Avago).

In the early 1980's, I designed a crystal
oscillator and buffer amplifier for the
HP 10816 rudibium standard.  The crystal
was a 10811 crystal and used the Colpitts
oscillator from the 10811.  The Colpitts
in the 10811 fed a grounded base amplifier
via the crystal.  In the 10816, I used a
cascade of 3 GB amplifiers.  This worked
better than the original 10811 buffer amplifier.

Rick

On 3/26/2016 10:57 AM, jimlux wrote:
> Consulting the time-nuts hive mind here..
>
> I'm looking for off the shelf connectorized amplifiers with very good
> reverse isolation for doing things like intermod measurements (e.g. 2
> signal generators followed by amps/pads into a combiner) and phase noise
> measurements for a digital receiver.
>
> 1-100 MHz kind of frequency range..
>
> I've used ZFL-500LN (30dB gain, 27 dB directivity in the data sheet,
> which I interpret as 57dB reverse) , ZX60-4016 (really more of a
> microwave amp, and not so hot reverse wise.. 25 dB)
>
> I'm not particularly cost constrained, so a higher power amp (which also
> reduces distortion products from the amp) followed by pads is always an
> alternative.
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