[BVARC] Antenna help

John Denison kd5you at comcast.net
Wed Jun 19 21:20:45 CDT 2024


To elevate it, use the force. 🙂

73
John Denison
KD5YOU

On 6/19/2024 8:24 PM, Andre Pollard via BVARC wrote:
> Thanks all for the feedback. No chance to work on it today, even if 
> the weather had cooperated.
>
>  I can get it to work fine on 20M and up, and since the trip starts 
> soon, I'm going to try it again when we get back. Going to try another 
> testing location to rule out interference that only seems to affect 
> 40M, since the current location is fairly near the house (stucco with 
> metal lath), and buried electric lines. Also will try different coil 
> settings and grounds. I will try to elevate it too, but since this is 
> my hiking antenna I'm not sure I want to add a tripod LOL.
>
> Andre
> W4SFZ
>
> On Wed, Jun 19, 2024 at 4:09 PM John Denison via BVARC 
> <bvarc at bvarc.org> wrote:
>
>     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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