[BVARC] Antenna help

[Jeff Greer]

Could you add a wire to the top of the whip, throw it in a tree or something, and turn the whip in to an inverted L?  Agree that the coil should work (maybe add more radials?), but the L might be something different to try.  (If you get the same SWR result, that probably indicates not enough metal on ground for the radials side...)
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From: BVARC <bvarc-bounces at bvarc.org> on behalf of Andre Pollard via BVARC <bvarc at bvarc.org>
Sent: Tuesday, June 18, 2024 4:19 PM
To: BRAZOS VALLEY AMATEUR RADIO CLUB <bvarc at bvarc.org>
Cc: Andre Pollard <apollard310 at gmail.com>
Subject: [BVARC] Antenna help

I need one of our antenna gurus to give me some input-

I have an 18'-4" telescoping antenna I have been using when camping. By adjusting length, I can get it to tune at <1.5 SWR on all bands 20M and above. So far so good, but when do we ever leave well enough alone.

I'm getting ready to travel for a while, and wanted to extend the range down to 40M. So I used the calculators at Coil-Shortened Vertical Antenna Calculator (66pacific.com)<https://www.66pacific.com/calculators/coil-shortened-vertical-antenna-calculator.aspx> to determine the necessary coil. It said I need 4.9 mH. I made the coil per the calcs one the same site, using a 1.9 inch diameter PVC pipe. I'm running it bottom-loaded.

By tapping the coil a couple of turns down, I can get it to tune to 7.2 mhz, but the SWR is >6. If I put my hand very close to the coil , the frequency shifts (expected), and the SWR drops to 1.2. So I tried adjusting the length and tapping different turns, never better than 4 SWR on any frequency around 7 mhz. However, if I get my hand near the coil, SWR drops.

Thinking this meant I needed capacitance, I tried a hat to the whip, with several different designs and sizes. Changes frequency, but horrible SWR still.

Bypassing the coil I can adjust the whip and get great SWR on 14 mhz and above. So, I don't think it's a problem with the coax (20 feet of RG8X) or nanoVNA.

Google shows up all sorts of sites showing making a coil loaded shortened vertical like i'm trying. None mention the issue I'm seeing as a problem.

I'd appreciate any input, I've been 'learning' on this for a couple of days now and haven't gotten it to work yet.

Thanks,
Andre
W4SFZ
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