[time-nuts] high rev isolation amps

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Mar 26 18:56:45 EDT 2016


On Saturday, March 26, 2016 10:57:01 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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These seem to be somewhat scarce.
One option is to add a unity gain high reverse isolation amplifier after your 
favourite low noise RF amp.
Even these are scarce so constructing one may be your only option.improve 
distortion.
A direct coupled series chain of CB stages should suffice.
Either a push-pull setup or applying feedback around the first stage emitter 
will input  
Packaging and cable leakage may limit the achievable reverse isolation to a 
bit below 120dB.

Bruce


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