[BVARC] Antenna help

Andre Pollard apollard310 at gmail.com
Tue Jun 18 16:19:16 CDT 2024


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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.bvarc.org/pipermail/bvarc_bvarc.org/attachments/20240618/6d5b6536/attachment.htm>


More information about the BVARC mailing list