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-----Original Message-----
From: George T. Daughters [SMTP:gdaught6@pobox2.stanford.edu]
Sent: None
To: yo3ctk@alltrom.ro
Subject: Re: [AMPS] IMD measurement scheme
(snip)
> Feed the PA with two signals of equal level with a known
spacing (say
> two kHz) and tune the receiver to each of the two tones.
how do you recommend this be done? a combiner/splitter? a
resistive
mixer? (high power resistors would be necessary) what's your
method?
During my career as a R&D engineer for military equipment in the
eighties, I used the following setup for measuring IMD performance of
power amplifiers:
A pair of HP signal generators (non-synthesized, for low phase
noise) feeding two power amplifiers (Marconi, 150W) connected to the
tested amplifier's input via a -3 dB hybrid combiner. This combiner must
have at least -40 dB crosstalk between its two inputs. We made it on a
Philips toroid, but I am sure that it can be replicated with Amidon
toroids as well. If you are really interested, I can dig into my notes
from that era to search for construction details. But I think it was
nothing unusual, just carefully made and designed for this power level.
At the output of the amplifier under test, we used a -40 dB, 1
kW power attenuator (Rohde&Schwarz) and either a HP 141T spectrum
analyzer or a Rohde&Schwarz test receiver. I personally prefer the
spectrum analyzer due to its ease of use, but Tom has a valid point in
that a good test receiver has a superior dynamic range.
Hope this helps.
73 de Mike, YO3CTK
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