[TowerTalk] Circularly Polarized Receive Antenna

[David Gilbert]

Yes, that's definitely true.  In addition to a couple of NanoVNAs and an 
HF-CIA, I own an FA-VA5 designed by DG5MK that also works with the 
DG8SAQ software.

By the way, it is possible to achieve the same thing as a TDR with 
almost ANY decent quality complex impedance analyzer even if it doesn't 
have TDR built in.  Just take R +/- jX measurements at three different 
frequencies on an open or short line, load those readings into TLW, 
visually inspect on the peak impedance plot (the button lower right on 
the TLW user interface) where along the line the readings match to get 
the velocity-factor-adjusted wavelength, and then use that to get the 
full length of the line.  It's a lot easier than it sounds.  I've done 
it on 20 to 30 foot lengths of coax and gotten results within a half 
inch of what I measured with a tape.

Dave   AB7E


On 8/17/2025 4:56 PM, Jim Brown wrote:
> On 8/17/2025 2:30 PM, David Gilbert wrote:
>> Even if you have "equal" length feedlines they don't necessarily have 
>> exactly the same velocity factor.
>
> Of course, and with instrumentation capable of TDR, we can measure and 
> trim their electrical lengths to match. I'm using the excellent DG8SAQ 
> VNWA, built and sold by a ham in the UK. It implements TDR by 
> performing an inverse FFT on wide frequency sweep. We can select from 
> a half-dozen windowing functions for the best view of the data.
>
> 73, Jim K9YC
>
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