Tuning a POTY

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EA7KIR
Posts: 67
Joined: Tue Feb 09, 2021 3:38 pm

Tuning a POTY

Post by EA7KIR » Thu May 26, 2022 5:24 pm

I bought a ready-built POTY and I'm Im not too impressed with the workmanship, so I'm trying to tune it with a NanoVNA V2 for the wide band QO-100 transponder. The plot shows my best effort so far, although resonance looks a little high and I don't see a double dip. So I'd like to know if this is as good as it gets. Any help welcome.
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Plot #1.png
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Michael EA7KIR

g0mjw
Posts: 1902
Joined: Sat Sep 20, 2014 9:15 am

Re: Tuning a POTY

Post by g0mjw » Thu May 26, 2022 6:34 pm

It is looking OK. You want to get the tip of that loop as close to the centre of the smith chart in the middle of the band. You might not see a double dip, it depends on the impedance and phase, best use the smith chart. Don't go for the best match possible, that is sure to be wrong. The circular polarisation depends on the two resonances not being on top of each other. It is also somewhat compromised by the large 22mm tube passing through the patch.

Mike

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