Robert A. Miller wrote:
wrote:
Yep, my point was that anyone with an MFJ-259B, like mine, can optimize
their own G5RV for true all-HF-band operation especially if they have
a built in autotuner like my IC-756PRO. One complaint I hear is that
the built in autotuners won't tune a G5RV on all HF bands. Well, here's
one way to solve that problem.
I'm guessing you have no coax here? Just ladderline from antenna to
rig?
No, no, no! In every respect, my antenna is a G5RV using RG-213 from
the ladder-line series section transformer to the hamshack. If someone
has a G5RV, he can modify it to work virtually perfectly on all HF
bands, including the coax feed. Everything about the G5RV remains the
same except the ladder-line length is modified, and in the case of
75m, a parallel cap is installed. These modifications are super easy.
As an example of virtual perfection on 3.8 MHz, the ladder-line is made
25 feet long and a 1000 pf parallel cap is installed at the ladder-line
to coax junction. The impedance at that junction is very close to 50
ohms resistive so coax is acceptable. Exactly the same techniques can
be applied to all the other HF bands, most of which require no parallel
impedance of any kind.
I will publish the details for each band as I work them out. But this
antenna of mine is a G5RV in all respects. It is a 102 ft dipole fed
with 20-36 feet of ladder-line. The SWR on 3.8 MHz is high so the 1000 pf
capacitor is needed to rotate to 50 ohms through the 1/50 conductance circle.
For the uninitiated, if you have a 25+j25 impedance, you can cause that
impedance to twist to 50+j0 ohms by installing a parallel capacitor. On
75m, that capacitance value is about 700 pf. My antenna works best with
a parallel 1000 pf capacitance on 3.8 MHz.
All G5RVs can be modified to work perfectly on all HF bands. The G5RV
has gotten a bad rap because no one has published those modifications.
But it is actually an excellent all-HF-band antenna. It takes me about
two minutes to change bands from 75m to 40/17m. And, for the lazy, that
change could easily be automated.
--
73, Cecil, W5DXP
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