[time-nuts] Reverse isolation

John Ackermann N8UR jra at febo.com
Sun Mar 8 22:48:58 UTC 2009

I've been learning a little bit about this lately from my friend who is 
an Agilent network analyzer apps engineer.

He tells me that "hot S12" tests can be done with modern network 
analyzers.  The key is being able to offset the frequencies enough so 
the front end of the analyzer doesn't get creamed.  For example, you put 
+10dBm at 11 MHz on the input, and +10dBm at 10 MHz on the output.  Then 
measure S12 using a narrow bandwidth in the analyzer.  Hopefully the DUT 
frequency response is flat enough for that to be meaningful.

In any event, it's a challenging measurement.


Didier said the following on 03/08/2009 06:14 PM:
> This question is directed at Bruce, but if anyone else has a contribution,
> feel free to speak.
> Bruce, 
> What is the best way to measure the reverse isolation of an amplifier
> (particularly a buffer amplifier for a 10 MHz reference), when it is
> expected to be in the order of 100 dB or more?
> Feeding the output with a known signal and measuring at the input with a
> spectrum analyzer comes to mind, but I am sure there must be something wrong
> with that technique, it sounds too simple.
> The presence of a signal at the input (or not) may affect the operating
> point of the amplifier, so measuring from output to input without such
> signal may not give a true result. 
> Didier
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