I have done it with these methods: One is to find or build an operating
impedance bridge. A Delta Electronics OIB2 is the module that was made
for HF range up to 1 kW. It will read inline impedance under power.
Another is to use an external dual directional coupler, rated for few
hundred watts and down to HF range. Werlatone makes such a device. You
might find something from Narda or Microlab/FXR surplus, not sure they
will go that low. Then calibrate it into the test using a vector network
analyzer. It has to have ext A/B/R inputs for this to work.
There are other ways, these are the most direct, and unfortunately
costly ways. But they will give you the exact input complex Z of an
amplifier under power.
73
John
K5PRO
Date: Fri, 22 Dec 2017 14:11:13 -0700
From: Steve London <n2icarrl@gmail.com>
To: amps@contesting.com
Subject: [Amps] Operational Input Impedance
So, this begs the question: What is the actual input impedance during
operation ? How would one go about measuring it with something like an
antenna analyzer or VNA ?
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