On Sunday, November 16, 2014 12:53:27 PM UTC-6, FBMboomer wrote:
I do not take the advice of those
who use what are supposed to be antenna modelling software that consider
all variables. They never do.

Antenna modeling is quite useful, and quite accurate as long as you
consider the possible faults, and quite useful as a learning tool.
I've modeled half a gazillion antennas, and most all were quite
accurate as long as you don't run into one of the few "gotcha's"
that can occur. That is normally not a problem with the vast majority
of antennas one would model.


Now, if a G5RV can be made to
work as well as a 1/2 wave dipole, I am guessing that it is not easily
done.

It's quite easy. Just ditch the designed for 20m feed system and
replace it with something more suitable for 75m.
The best would be to use a tuned ladder line, or a tuned open wire
line. Of course, you would need to change the lengths of the tuned
feeder if you change bands, but that can be done with knife switches,
etc..
The 2nd best would be to feed it with an untuned ladder or open wire
feeder, and use a tuner at the shack. The tuner loss won't be huge,
and it will perform better than the usual garden variety G5RV.

Myself, I would prefer to use a 130 ft dipole, and feed like this if
I were to use a tuned feeder.
http://www.w5dxp.com/notuner.HTM
But you can feed a 102 ft dipole the same way if you vary the feeder
length for a good match, with good results.

I have never heard a G5RV that was anything but lame. Perhaps
everyone puts up the G5RV using short cuts. I don't know.

No, they are just using the garden variety G5RV, which was designed
as a 20m antenna. And many use a tuner at the shack, which adds even
more loss.

Using an untuned ladder or open wire line with a tuner at the shack
should give quite an improvement over the usual 20m method most newby's
use. That's the easy way out for a decent improvement.

Now, feeding a half size dipole with the same method can lead to some
pretty serious losses if one uses a T match tuner, etc. You would want
to avoid that. I always prefer a 1/2 WL dipole for the lowest band
to be used to avoid that if feeding with ladder/open wire line and most
common tuners "IE: T match, etc" at the shack.

But I've always preferred coax fed dipoles and such. The coax fed turnstile
is one of the best NVIS antennas for the low bands I've tried so far.
Low feeder loss same as a 1/2 wave dipole, and also no tuner required.
And you can even steer the pattern a bit if you rig up a way to change
the phasing between the two crossed dipoles.

The horizontal loop is a good NVIS antenna, but I could see no real
advantage over the dipole or turnstile when considering the extra hassle
of installing one. But I wasn't worried about local noise even though
I'm in the city.
Evidently the pattern you are getting from yours has pretty low gain
at the low angles, which is likely why you are hearing less local noise.
Which is fine. But you have to consider that antennas are generally
reciprocal between transmit and receive, so if you are hearing less
noise at those lower angles on receive, you will also transmit less RF
at those same low angles. With a NVIS antenna, not really an issue though.
For DX, it would likely be inferior to the previous dipole you used.

And modeling should show you the difference between the two patterns
at those low angles quite accurately.