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Topband: Flag Xfmr Measurements

To: <topband@contesting.com>
Subject: Topband: Flag Xfmr Measurements
From: W8JI@contesting.com (Tom Rauch)
Date: Fri, 13 Sep 2002 21:52:08 -0400
> I fail to see how you can possibly have a VSWR of 5:1 when you
> terminate your matching transformer with 900 ohms and look at the 50
> ohm side.  You have the turns ratio correct for 50 to 900 ohm
> impedance transformation. 

I'm not saying anything one way or another about this because I 
haven't followed the discussion that close, but there is something to 
keep in mind.

Transformers and matching systems with loss are not symmetrical when 
reversed. In other words, a perfect SWR 9:1 step down transformer is 
not 1:9 when used to step impedance up (between the same impedance 
ratios) if it has loss. This creates a real problem when measuring 
performance and loss with back-to-back identical transformers or 
matching systems with loss.

We should never assume a RF transformer or matching network is 
symmetrical, unless we know for sure it is nearly lossless.73, Tom 
W8JI
W8JI@contesting.com 


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