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@sdellington.us
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