Cecil Moore wrote:
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.


As a G5RV is to a dipole, is your modification *really* a G5RV? Seems
to me that you have a ladder line and capacitor tuned dipole, not a G5RV.

Does the 102 foot dipole have to be called a G5RV? Heck, Cecil - you
might just be able to call this the W5DXP antenna. Seems different
enough to me! 8^)

And perhaps your modifications actually show a little bit of why the
G5RV gets a bad rap! 8^)

In the interim, I'm watching this with great interest. It might just
be a great solution for me. I can get 102 feet of wire up. I have 96
feet with a tuner now.

Do You switch the capacitance in and out, or use variables? And if you
switch, do you have the caps at the coax ladderline junction or in the
shack?

Possible really stupid question alert!: When you speak of the ladder
line being 20-36 feet, and or 25 feet for 3.8 mHz (with cap) you mean
that the total height from the coax/ladder line junction to the antenna
itself must be the length of the shortest piece of tuning ladder line?

IOW, If I run my coax to the roof of my house to the box I would
construct to hold the different lengths of tuning line and switching
electronics, I could only have the antenna roughly 25 feet above this
box? If so, I can still probably get the antenna 50 feet above the ground.

Any problems with rolling the ladder line?



- Mike KB3EIA -