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Re: [TowerTalk] Test Fixture for Common Mode Chokes

To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Test Fixture for Common Mode Chokes
From: Brian Beezley <k6sti@att.net>
Date: Fri, 23 Jan 2026 18:18:44 -0800
List-post: <mailto:towertalk@contesting.com>
AC0C said:

"Brian, would you consider the N2PK VNA in the "fancy" category rearding your calibration comment?"

Jeff, I don't think the N2PK measures all four S-Parameters nor does it do a 12-term calibration. I was thinking of the HP 8753C and 8753D, which are sophisticated VNAs that a surprising number of hams have.

I confused some things in my last message. The NanoVNA compensates for the port 1 impedance when doing a single-port calibration, but I don't believe the stock firmware compensates for it when doing a two-port calibration. Also it is the port 1 impedance that was so far off for the particular NanoVNA-H4 N6LF tested, not port 2.

I'd be interested in seeing an .s2p file for the commercial test fixture. If the S21 method is good enough without going to the trouble of making a Y21 measurement, that would be good to know.

Brian

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