[TowerTalk] EFHW core
K9MA
k9ma at sdellington.us
Tue Sep 29 14:15:54 EDT 2020
I went through a similar exercise with a 40 m EFHW for 40 and 20. It is
true that the full wave resonance is not exactly twice the full wave
one. I designed and built a small QRP tuner specifically for this
antenna. It has a pretty wide resistance range, like 2K to 6K, but
limited reactance range. Some modeling told the length of wire that
could be matched on both bands. It works fine. Although I never
considered 15 meters, it turns out to work there, too. Then one day I
heard a station I wanted to work on 30 meters. Much to my surprise, I
was able to get it down to 1:1 and worked the station. That was purely
an accident, and I'm sure it wasn't very efficient with the 2 meter
counterpoise I use for the other bands, and I wouldn't try that with
more than 5 W.
73,
Scott K9MA
On 9/29/2020 12:39 PM, Richard (Rick) Karlquist wrote:
>
>> _______________________________________________
>
> This marketing claim strains credulity. I used to have a
> half wave end fed wire cut for 80 meters @ 50 feet. It had no more
> bandwidth than a typical 80 meter dipole. I had a matching
> network with a tapped coil and a motorized switch to cover
> the band in 100 kHz steps. The impedance was around 3,000 ohms,
> which is very roughly 50 X 75 ohms. On 40 meters, it functioned
> as a full wave end fed. However, the resonant frequency was
> above the 40 meter band, and it had to be tuned down using
> a switched in capacitor. The drive impedance on 40 was
> considerably lower. After much due diligence, I was able
> to make a usable 80 and 40 meter antenna. I made my first
> clean sweep in SS using it (plus my KT34).
>
> The idea that a simple transformer could cover all the bands
> from 75 to 10 meters with no tuner is simply not believable.
> I see that there are no specs on SWR, etc. Then there is the
> issue of the various patterns on the various bands. No cleverness
> at the drive point mitigates this.
>
> Rick N6RK
> _______________________________________________
>
>
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--
Scott K9MA
k9ma at sdellington.us
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