[TowerTalk] TowerTalk Digest, Vol 278, Issue 4

[JAMES WOLF]

Tom,

Ideally, you would include the feedline in the calibration of the test device. That's not usually practical either.  What you can do, is to calculate how the feedline transforms the measurement.  To do so, you need the impedance of the line, the velocity factor, and the loss at the frequency of measurement.  Then you can model the feedline as a transmission line. attached to the source (antenna).  You should be able to use a program such as TLDetails to do the math.  https://ac6la.com/tldetails1.html


Jim - KR9U  




> On 02/10/2026 5:00 PM GMT towertalk-request at contesting.com wrote:
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> Today's Topics:
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>    1. Antenna Analyzer Question (Tom Hellem)
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> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 10 Feb 2026 07:37:48 -0700
> From: Tom Hellem <tom.hellem at gmail.com>
> To: towertalk <towertalk at contesting.com>
> Subject: [TowerTalk] Antenna Analyzer Question
> Message-ID:
> 	<CANyX0ApfgyW=q=a8i119-fws6Xs=CXyyskpMK8YKE=wgnUEfrw at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
> 
> In order to make measurements  of impedance, etc on an antenna with any of
> the various analyzers on the market, one must connect the analyzer to the
> antenna
> with some length of coax. And unless the antenna being measured has a
> feedpoint
> impedance of 50 +/- j0, the impedance as seen by the analyzer is going to
> vary
> continuously all along the length of the coax, a phenomenon easily seen
> with the use
> of a program like TLW, etc.
> 
> Question is, unless I can attach the analyzer directly to the feedpoint,
> how can I
> obtain a reliably accurate measurement?
> 
> I just looked at the user manual for one of the popular analyzers on the
> market.
> It makes no mention of this whatsoever. And I don't remember it being in
> any other manual I have seen in over 50 years of being in ham radio except
> for one:
> I have a manual for  a simple and inexpensive VNA built from a kit several
> years ago, sold by a German company, that makes a big deal out of doing
> what it calls an SOL compensation for
> the coax and any other connectors used between the VNA and the antenna.
> This
> supposedly removes any of the impedance transforming effect of the test
> setup from the
> equation and allows for a precise measurement of the antenna under test.
> 
> So what gives? Has anybody here ever wondered about this?
> Am I overthinking it or is there something to it?
> 
> Tom
> K0SN
> 
> 
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> End of TowerTalk Digest, Vol 278, Issue 4
> *****************************************