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Re: [TowerTalk] More Radials = Higher SWR???

To: towertalk@contesting.com
Subject: Re: [TowerTalk] More Radials = Higher SWR???
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 5 Feb 2023 20:41:14 -0800
List-post: <mailto:towertalk@contesting.com>
On 2/5/2023 8:18 PM, Lux, Jim wrote:
I just do a cal with the coax, putting the O,S,L at the end. Then between that measurement, and the no coax cal, you've got the S21 for the Coax, which most of the tools will de-embed if needed.  You could probably just do a "open" measurement and it would be good enough to measure the coax.

I guess if you've got an antenna up on the tower, that's a bit harder.

The only antennas I can access to do that are RX antennas and 160M verticals.

(although I suspect someone could come up with a scheme where you look "off resonance" where the antenna impedance is wildly off resonance, and then interpolate)

As you probably know, it's easy to get good TDR data with an antenna connected, whether some form of impulse or inverse FFT of swept impedance. An impulse is inherently broadband, and because a very wide sweep is required for decent distance resolution, nearly all practical antennas are resonant over a small fraction of the wide sweep, there will be a strong reflection at all frequencies where the antenna is not resonant. I typically sweep 50-550 MHz so as to avoid the part of the spectrum where VF is most variable.

73, Jim K9YC


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