Hi Andre
I was going to mention the 33' counterpoises, but I see that you have
done that already. I've used a single counterpoise on 40 meters with
various coil antennas. One thing I didn't see in any of the emails is...
where are you setting up your antenna? Is there anything metallic nearby?
I have a Wolf River Coils Take It Along mini which is good for 40 meters
and up, and I found that I can tweak the resonant frequency by rotating
the sleeve around the coil rather than just moving it up and down. I use
either the stock WRC telescopic whip or a Buddipole extended length whip
used for 80 meters. Both are roughly 10 feet long.
I typically achieve better results with vertical antennas when they are
elevated above the ground. i.e. 4-5 feet vs .5 foot above the ground,
though I was never able to get any results comparable to an inverted V.
With a manual tuner I was able to make the transceiver happy while still
being able to use the antenna to some degree of success, but it took a
steady hand and very miniscule changes in the capacitance knobs.
73
John Denison
KD5YOU
On 6/18/2024 4:19 PM, Andre Pollard via BVARC wrote:
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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