Well, Tom I operate from a small city lot, although I do have some tall
trees! I've done OK on 160 and 80 with a 160 inverted L and full size 80m GP
- both with elevated resonant radials. (The 160 radials did meander a bit)
I've worked some really good DX on 160 - VK6, 3B8, JA and 3Y0 etc. - and
some deep Russians. Biggest problem for me, in the city was not being heard,
it was HEARING! Once I put up a terminated loop "Kaz" antenna, with a
preamp for receiving. All that changed - a LOT! I believe that guys are
missing a good bet by not trying the elevated resonant radials under their
160 and 80m antennas -even if they have to meander a bit.
In my experience,the main challenge on 160 is HEARING!
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Tom W8JI
Sent: Wednesday, December 12, 2012 4:25 PM
To: Guy Olinger K2AV; Ashton Lee
Cc: k6xt@arrl.net; topband@contesting.com
Subject: Re: Topband: Fw: GAP VERTICAL QUESTION
With the following caveat: The very sparse and short buried radial systems
he is showing are FAR more lossy in practice than shown in his gain tables.
Four twenty foot buried radials beneath a 1/4 wave L on 160, could place
you down 20 dB. >>>>
1% efficiency, and 99% of power dissipated in the earth with a small ground
system on an inverted L antenna? I don't think that is very likely without
a feedpoint in the hundreds or thousands of ohms. Even a single ground rod
is likely around 50-100 ohms, and would produce signals much stronger than
that.
There are ways to create modest feed impedances with extreme loss.
Researchers at GAP, through great effort, have found a way to combine
terrible efficiency with a reasonable feedpoint impedance.
Based on measurements, the GAP is somewhere around 1% efficiency on 160 and
around 3% efficiency on 80 meters. Most of this loss is because the loading
system (at least in large part) uses a coaxial stub, which has a Q low in
the double digits, and has higher voltage applied at a poor ground system.
I'm also sure much of the loss is caused by folding of current back and
forth, cancelling radiation and driving radiation resistance through the
floor. The bulk of the feed impedance on low bands is dissipative. It is a
very high angle radiator on ten meters, but is "OK" on most other bands.
This is quite an achievement, giving low SWR and mobile-antenna performance
without actually using an antenna 8 feet long, and without a physical
resistor.
<<
You really can't do that as your 160 meter counter poise and expect decent
results. You can end feed the same wire on 80/40/30 meters (full wave worth
of wire in the L on 80m) >>>
It is a half wave on 80.
<<<with four buried 20 foot
radials and it will be an excellent antenna. This is due to the high Z feed
at the ground with current max AWAY from the feed point.>>>
Four short radials on an L are really not that bad compared to an antenna
engineered to have very low radiation resistance and very high internal
loss.
I know or knew people who were quite successful with small grounds on
inverted L's. An old friend (now SK) in Toledo had an inverted L on a small
city lot, probably no more than ten feet deep from the house to the fence,
and he was consistently within a few dB of my full size 160 vertical in a
swampy area. His only long radial ran parallel to the L and underneath the
L. His radials were buried to hide them, and his L was right against his
ranch style house.
Other people had similar antennas. One fellow had nothing but ground rods,
he had no radials at all, except the wires that connected the rods. His
signal was certainly less than my 1/4 wave tower with a large radial system
in wet black sandy loam, but it was probably not more than 5-10 dB less.
Another station was always within an S unit on any report anywhere, even
Australia, and he was on a corner city lot with less than 20 feet to the
sidewalks for radials and a 30-35 ft high inverted L.
My conclusion is it takes great effort, or significant incredible failure,
to manage to be 10-20 dB down.
I really get quite a chuckle out of anecdotal day-and-night performance
reports, when I think back at some of the absolutely rubbish that ran neck
and neck with a quarter wave vertical in black wet swamp soil. I wonder more
about how poor the one antenna was than how good the second one was.
73 Tom
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