On Sunday, November 16, 2014 4:47:35 PM UTC-6, gareth wrote:
wrote in message
...
It's quite easy. Just ditch the designed for 20m feed system and
replace it with something more suitable for 75m.

But the 102 ft top together with the 34 ft ladder is designed for 3.5MHz!

Not exactly.. It's a bit long when used as the makeup section
on 75m. But I believe it's the use of the chokes which cause the
losses many people see. Many claim it can be fairly efficient on 80m
using the standard G5RV with the 34 ft ladder line. On paper I suppose
it can if all clicks in an orderly military manner..

If...

And the various types of chokes are not created equal for this type of use.

I just don't like the design myself. On bands that show a large reactance
on the load side of the choke, you can saturate the core of the choke, which
turns RF to heat. No bueno..
In those cases, I think it would be better to ditch the choke and live with
the feed line radiation unless it causes problems.

I think it's kind of a mickey mouse design for my uses, but I'm spoiled
on the highly efficient coax fed dipoles, and see no reason to compromise
with lesser designs. Life is too short for compromise antennas unless one
actually needs one to fit the space, or really wants to work all bands
with a single wire up. That's not me.. I don't work the high bands that
much, and I have a tower and tri-bander I can put up if I really wanted to.
I'm not worried about room for the dipoles.
I can fit a full size 80m dipole no problem here at home, and I have
room for anything I can think of at the dirt patch.

I think ladder line all the way is the best for all band G5RV use, and is
the only way I would run one, if I were to run one.

I've also seen quite a few examples of excess choke losses on many of
the various commercial windoms.

I've never used a G5RV or windom myself, and I doubt I ever will, being
I can run full size dipoles. I've tried a few portable, and was not
impressed at all with the ones I used. One particular G5RV I once used at
a field day was fairly pathetic on 80m, and had me pulling my hair out.

Wasn't mine, so not sure on the type of choke, etc.. But it was bad news
vs a coax fed dipole. Terrible I tell you.. yuk.. I refused to ever be
stuck on one again after that, and always took supplies to build my own
dipoles on later field days. The next year, they were using a windom on 40m.
I strung up a coax fed 40m dipole also, and used a switch to A/B the two.
The owner of the windom was fairly shocked at the difference between the
two. I've talking 2-3 S units worth of difference on the rig's meter.
All signals, noise floor, the whole ball of wax was way up on the dipole.
And again, I lay most of the blame on the choke that was used more than
anything, but I've also never really been a fan of OCF wires either.
I guess I don't have to tell which antenna I used.. :|

I'd rather run parallel fed coax fed dipoles for more than one band. And
also, I rarely have a need to work all bands being as I run the lower bands
most of the time.
I generally work 80 and 40 mostly, so the parallel 80 and 40 dipoles fed
with a single coax feed is a better choice for me and is a highly efficient
system. I usually run the dipoles at right angles if possible to reduce
interaction, which can sometimes cause tuning quirks for the higher band
dipole. I never run them closely stacked like some do unless no other choice.

And that will work some of the higher bands with a reasonable SWR on the
harmonics if I want to take a walk on the wild side and work a higher
frequency. I just slap a tuner inline as a line flattener and live with the
losses, which will vary to the quality of the coax and the band used.
Some parallel dipole setups I also add 160m legs, but if I don't, I just
tie the coax together at the shack and feed as a T vertical on 160m,
which often is just as good, or even better on longer paths.