output impedance

[Ignacio Omeñaca]

 

Hi guys, any suggestion  how to measure the output complex impedance of an RF amplifier?

 

Using a NANO VNA?

Measuring voltage, current and  phase with an oscilloscope and calculate the impedance?

 

Basically I would like to figure out the  output impedance of a  Chinese amplifier (HF and VHF) to calculate matching network and filters

 

 

Thanks

 

73

 

Nacho

M0IXG

EA2AIV

[John Gumb]

Nacho,

The “right” way to do this appears to be with a “load pull set”

https://www.microwaves101.com/encyclopedias/load-pull-for-power-devices

https://www.everythingrf.com/community/what-are-load-pull-measurements

as no doubt you’ve found. Read that lot for too long and you brain dribbles out of your ears :-;

I’m wondering if it can be done using an ATU and dummy load & power meter. Maximum power transfer will occur when the source and load impedances are matched. Get a match with the amp driving into the ATU and dummy load & power meter then read it back using the analyser. You’d have to be careful about spurious responses/oscillation in the amp. I guess you’d have to try a selection of frequencies. Also it takes no account of what’s going on at the input. Also, I guess there will be many possible matches.

This is a problem I’ve been curious about.

Hopefully one of the grown-ups will respond :-) Someone must have done it.

73 & great to hear from you.

John

G4RDC

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[Gary Searle]

Back to front measurements. Interesting John.

DE G4ELD

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[Ignacio Omeñaca]

Thanks John, very interested readings for this weekend…

 

I am tempted to put the amplifier on TX grounding the input and use a NANOVNA to measure the output impedance and  hoping not to see smoke

 

 

73

Nacho

M0IXG 

EA2AIV

To view this discussion on the web, visit https://groups.google.com/d/msgid/radarc/A4BAE253-7C9F-467D-B661-77267A3A6684%40gumb.org.