[TowerTalk] Antenna Analyzer Question

[Jeff Blaine]

Tom, you are absolutely correct.

The very very very cool part of a VNA-type device is the ability to move 
the "calibration point" to the end of a length of coax (using the OSL).  
This frees you from having to connect the device right to the 
feedpoint.  Some SWR meters (like the Rig Expert devices) also support 
this capability.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 2/10/2026 8:55 PM, David Gilbert wrote:
>
> That's every bit as technically correct  as anything I said ... it 
> just requires that you cut a piece of coax to a particular length so 
> it's not quite as versatile.
>
> But just as valid.
>
> Dave   AB7E
>
>
>
> On 2/10/2026 6:59 PM, john at kk9a.com wrote:
>> While not as technically correct as the responses from AB7E, K9YC and 
>> W6RMK,
>> what I used to do back when I used Yagi's with hairpin matches was I
>> measured the impedance through a 1/2 wl multiple of coax.
>>
>> John KK9A
>>
>>
>> [TowerTalk] Antenna Analyzer Question
>> Tom Hellem K0SN 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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