[TowerTalk] Antenna Analyzer Question

[David Gilbert]

As you say, the coax can make significant changes between the impedance 
at the antenna and what you read at the near end of the coax.  Like 
huge.  Here are two methods to deal with that.

1.  Use TLW or TLD to translate what you read at the near end of the 
coax to what it actually is at the far end of the coax.  It's simple to 
do if you know the length of your coax ... and what kind of coax it is.

2.  Calibrate your VNA with the OSL elements at the far end of the coax.

I've used both methods in the past, and either will work.

Dave   AB7E


On 2/10/2026 7:37 AM, Tom Hellem wrote:
> 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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