[Amps] Operational Input Impedance

[John Lyles]

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 at gmail.com>
> To: amps at 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 ?