John is absolutely right, however a compromise antenna is better than no
antenna, and it's amazing what you can work with a compromise antenna when
the band is open to you. I live in East Central Iowa. I'm real estate
challenged, as in a suburban back yard that measures 60x70 ft., and I'm
height challenged to 54 ft. because of FAA restrictions. My inverted L for
160 runs up a 48 ft. tower to 46 ft., then slopes downward 58 ft to a 26 ft.
pole in the center of the back lot line, then horizontal to the East for 35
ft. at a height of 26 ft. where it's tied off to a pole on the Northeast
corner of the lot. The tower is right next to the house in the middle of the
lot, so I don't have any radials, just an 8 ft. ground rod. My SWR,
unmatched, is 1:1.4 at 1.828 MHz (think warm worms). I have a TH-11 on the
tower, a HF2V on the West side property line between my house and the
neighbor's house (also no radials), a mag loop on the East side property
line between my house and the other neighbor's house, and a Waller flag on
the North property line (right under the inverted-L! The most I've ever
gotten out of my amp is 800 watts. With this severely compromised antenna
farm, I've confirmed 295 on 30 meters, 278 on 40 meters, 219 on 80 meters,
and 131 on 160 meters. I didn't get on top band until October 2003, but I've
been on the other low bands since 1982.
All this is to encourage other challenged top band (and low band) hopefuls
to do the best you can with what you've got. You may not be able put up a
perfectly matched antenna with high radiation efficiency, but shouldn't
prevent you from working some pretty good DX. I confirmed zone 18 on top
band, and that's right over the pole from Iowa. When it comes to antennas,
anything is better than nothing.
Nelson, KU0A
-----Original Message-----
From: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
On Behalf Of John K9UWA
Sent: Friday, October 14, 2011 7:55 AM
To: topband@contesting.com
Subject: Re: Topband: Fwd: Capacitor for Inverted L
With a 30 foot high vertical section and the rest around 105 feet horizontal
And having two above ground radials. The "Real Impedance" Of this antenna is
about 12 ohms. The fact that the antenna matches 50 ohm coax says that your
"Ground Loss" of this antenna is about 38 ohms. So your
warming the worms with about 3/4 of the power going into that antenna
and only 1/4th of the power is actually being radiated into the air. If you
keep
adding additional radials you will find that the match will keep lowering
until
eventually at around 80 to 100 radials you would eventually get to a ground
loss of maybe 5 to 10 ohms the antenna would be much more efficient. It
would then require a 2 to 1 Un Un to match the now around 25 ohm antenna
to your 50 ohm coax. Your signal will be considerably stronger as you won't
be warming the worms as badly as you are now.
John k9uwa
> Although I'm far from being an antenna "expert", I second Wes'
> comments about matching a 160 meter Inverted L.
>
> I recently made my first ever Inverted L and am very, very pleased
> with the results. Mine has only 30 feet or so of vertical rise, and
> the remainder of the "hot" side runs pretty much horizontal. Being
> very space constricted, along with having to be stealthy due to HOA
> and CC&R issues, I was only able to get two radials installed. Both
> are 16" off the ground. When I first installed the antenna and hooked
> my MFJ-259B to it, it was resonant at about 1.700 MHz. I pruned back
> the radials several feet and left the "hot" wire alone. Doing so got
> the antenna to resonate at 1.840, with a 60 KHz 2:1 bandwidth. I feed
> it with 115 feet of RG-8 and have a huge coax RF choke at the feed
> point. With this "crummy" antenna setup I've worked the east coast of
> the USA during the recent California QSO party, in addition to easily
> working the guys at T32C. This has been with 100 watts from an
> Elecraft K3. The auto-tuner in the K3 has no problem getting a match
> up in the phone part of the band. N o external matching network
> needed here...! :-)
>
> I put my final measurements into EZNEC and the far field plot shows
> the antenna being omni-directional (expected), but with a fairly low
> take off angle - about 25 degrees. I fully expected that I'd wind up
> with an NVIS cloud warmer, but the on-air results pretty much compare
> with the modeling data.
>
> Jim / W6JHB
John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
k9uwa@arrl.net
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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