RadioBanter - View Single Post

December 20th 05, 12:46 PM posted to rec.radio.amateur.antenna

wrote:
I'll leave the theoretical howcums of my experince to those of you who
are deep into the physics of electromagnetics. For my part another 1/4
wave HF GP just ain't gonna happen here again elevated with radials or
ground mounted with gazzilion radials. ..........................

Kinda weird. The one I used here worked great. And almost
identical specs. Mine was full size at 36 ft with 4 sloping radials.
The only thing I can think of to explain it , would be ground quality.
Evidentally, my ground quality must be pretty good compared to
many areas of the country. I know it's a good bit better than Cecils,
judging by the conductivity maps. If your's didn't work up to par,

Hi Mark. What's your/any definition of "par"in this context? What other
40M antenna did you A/B test against your GP on the air?

I'd almost have to blame it on the radial system. I think you probably
needed a few more to equal what I had here. In fact, going by the
numbers, for a 1/4 wave at a 1/4 wave high, you really need 8 radials
to equal 120 on the ground. I judged my 4 radials as being equal to
about 60 radials for a ground mount.

No surprise there.

But...My conductivity rating in
this area is bordering on the "30" range being I'm not too far from the
coast.

.. . maybe someday I really will download that map . . Not that I can do
anything about what it tells me about the ground condx in my particular
neighborhood . .

I know for sure Cecil would need more radials than mine for
the same performance, as his was half the height and his ground
rating is lower. .
My hunch is if you had 8 radials on the GP, it probably would have
done better.

Maybe, maybe not but realistic modeling elevated HF GPs would at least
provide some hints. Maybe.

From what I've seen, heard and read over the years there's a whole
bunch of smoke, mirrors and mythology wrapped around the effects of
radials as they relate to current-fed HF verticals. Reg Edwards
"endfeed.exe ' ditty looks like it debunks a bunch of the mythology. In
any event and with all due respect I'm not about to get into
nit-picking any of it.

The situation I described was a sort of very subjective A/B "shootout"
between my two 40M antennas as transmitting antennas and the so-far
strange and unexplained results I got and I seriously doubt that my
results would have been noticeably different if the GP had four more
radials. My voltage-fed inverted L seriously and consistently
outperformed the GP on long-haul contacts as a *transmitting* antenna
to the tune of at least one s-unit, sometimes more particulary into the
north Pacific, at the far end. But the two antennas seemed even-up when
*receiving* on my end. That's the issue Cecil brought up. The only
"radials" I had under the L was a three foot long #14 wire which ran
from the cold side of the tuner to a copper-plated eight foot steel
ground rod driven a few feet into the ground. It BOOMED. The GP did
not.

My GP totally smoked the ground mount I had that used 32 radials.
No comparison at all.

Yup.

I've never tried 1/2 waves on the low bands,
except for extended inv-L's...I have run them 20m up though.
Work well there.

Seems like they work nicely. So far my only measurable current-era
experience with true ground-mounted half-wave "dipoles" came about when
I operated portable for an extended period a few years ago and strung a
coax-fed 20M dipole up into a big maple tree with the bottom end of it
a foot or so above the ground. Lousy location, halfway down a hill on
one side of a mini-valley but "I worked every station I called". Heh.
My alternative antenna then was 475 feet of wire strung thru seven
trees "resonated" by some MFJ rotary inductor clunker or another which
was "gounded" by 75 feet of wire from my third floor shack to the
nearest patch of grass. RFI disaster site. Zero RFI with the dipole.

Anyway I'm on my way into a new location. Tiny property which will host
several voltage-fed HF verticals because of their minimum-size
footprints. Along with the verticals the property also hosts a rather
swampy bamboo farm. Big suckers too, maybe I can raise my own quad
spreaders. What do you 'spose the ground resitivity and permitivity
might be? Reg and Nec-Win- Plus want to know . . .

MK

w3rv