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Author Topic: 160 Meter Antenna  (Read 511 times)
N1ZHE
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Posts: 68




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« on: December 04, 2003, 01:35:23 PM »

I live in a house with a very small lot.

My dipole is only 73 feet long, and won't resonate on 160, even with a good tuner.

What would be a good antenna to use for 160 in my case?

Has anyone tried the 160 meter Isotron?

David
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KT8K
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Posts: 1490




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« Reply #1 on: December 04, 2003, 02:18:14 PM »

From what I know of them, the Isotron is a pretty inefficient antenna.  A short vertical with a capacitance hat and a good ground radial system might be a much better answer. Dr. Jerry Sevick has done some great work on this and written about it in his books. Also check out ON4UN's book on "Low Band Dxing" and W4RNL's work at www.cebik.com.
A shortened antenna always has narrowed bandwidth and/or a big tradeoff in efficiency, but can still work well for you.
Good luck es 73 de kt8k - Tim
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K5DVW
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« Reply #2 on: December 04, 2003, 02:45:13 PM »

Unfortunately, small lots and "good" 160m antennas dont go well together. I've fiddled around with different ideas and the best thing I have found is a short vertical with a capacitance top hat. But, I've gone slightly farther and used inductive top loading right under the capacitance hat. In order to get any decent effeciency, you need radials, lots of them on the ground. What you'll find is that the VSWR bandwidth is exceptionally narrow, like on the order of 10's of KHz!!

The ARRL antenna book has an article showing how to build a 7' tall antenna for 40m in this manner. You could do the same for 80m or 160m.

Another thing that works is a low dipole, or NVIS or "grasswire" antenna. Try looking that up on the net and you'll find some ideas. They are both poor radiators, but you'll make contacts. When I tried these types of antenna, I could hear much more than I could contact.
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WB2WIK
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« Reply #3 on: December 04, 2003, 04:01:26 PM »

You might try a linear loaded loop surrounding your lot, occupying its entire perimeter.  A FW loop for 160 should be about 520 feet long, so if you had a square lot to fit a full-sized loop, your lot would have to be 130 feet square, or more than a third acre.  Sounds like you don't have that.

But you can put bends and folds in the wire to maintain electrical length while reducing physical length, and this works pretty well.

Do you have room for four corner supports for a loop?  If you do, there isn't much that will work better with limited space.

WB2WIK/6
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W3JJH
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« Reply #4 on: December 04, 2003, 04:07:04 PM »

I've had good luck with a Van Gordon Shorty Dipole on 160.  The antenna is 70 ft long with loading coils and is fed with ladder line.  I use a Centaur 4:1 balun just outside the shack and have a coaxial lightning arrestor on the coax that enters the shack.

The radiation impedance and, hence, the efficiency of an antenna depend on its size relative to a wavelength.  Small antenna such as the Isotron may match your transmitter quite well, but so will a dummy load.  Some dummy loads may also radiate as well as a small antenna.
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WB6BYU
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« Reply #5 on: December 04, 2003, 05:20:24 PM »

Probably the simplest approach would be to add loading
coils at each end of your dipole, with additional
wire extensions going out in whatever direction is
available for 10' (3m) or so beyond the loading coil.
(The wires could even hang straight down.)

How large of a coil?  I think the ARRL Handbook and/or
Antenna Book have design charts for loaded antennas -
if you can't find the ones for dipoles you can use the
ones for mobile whips with some extrapolation.  Seems
to me that "a hair curler wound with #22 wire" used to
be pretty close for the end of an 80m dipole, and this
would need something more than that.  Maybe about a
6" winding on a length of 1" PVC pipe would be a good
start.  Fortunately, just about anything you use will
help the tuner get a better match - even the wire
extensions without a loading coil.
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K4LIX
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Posts: 49




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« Reply #6 on: December 04, 2003, 06:06:45 PM »

See Nov. 1986 QST, page 26, "How to build a 160 meter Shortie" - I have one myself and have made a few for my friends - covers the whole band - 1.8 to 2.0 - no tuner needed - can also be adapted for 80/40 meters. --Good Luck, Jim--
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W8JI
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« Reply #7 on: December 04, 2003, 06:06:55 PM »

David,

Having operated 160 meters from all sort of locations since 1963, I'd never use anything on a small lot except an Inverted L.

A friend of mine, K8GIJ, lived on a city lot that was only about 30x120. He had about ten feet of backyard depth, and about 80ft wide.

He used a REAL open wire line up to an end-fed Zepp and fed the Zepp like a Zepp on 80 and higher. On 160, he fed it like an Inverted L.

Harold tied everything metal in his backyard to a ground, and fed the antenna with the feeder shorted worked against ground. He tied in the chain link fence, and everything he could with short direct wires to the tuner chassis.

When it was all done, he was always within a few dB of me and I had a 1/4 wl 130 ft vertical in wet rich black soil with 100 radials!!!

Another fellow with a *full size* dipole up 70 ft would be 5 S-units weaker than me at modest to long distances, and no louder at all in close.

I think using any horizontally polarized antenna on 160 is a mistake. Anyone with any serious time on the band will probably tell you the same thing. Low dipoles just get smoked by verticals. I have a 318ft tower and a hundred acres, and when my dipoles (some at 300ft) fell down, I never bothered putting them back up. It would be especially bad if you had loading coils.

While any antenna is better than no antenna, I'd seriously advise you try your best to get some sort of Inverted L up, even if you have to augment it with a loading coil. An additional plus is you can load it on other bands as a long wire with a tuner. Just be sure to do the best you can for a ground system.

73 Tom
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