Yeap, I use a folded unipole, and it doesn't have to be a "quarter wave"
to radiate well.
The system I proposed isn't of my invention,
but comes from an old (and highly respected) antenna text, Laport's "Radio
Antenna Engineering", my copy dated 1952. He proposes using the wires in
or on the ground, and also shows a neat "unbalanced" line built in what
looks to me like raingutter turned upside down. He admits the losses are
higher than balanced line because of the return currents in the lossy
earth and that there will be radiation from the line. He also shows a
number of multi-wire configurations which are unbalanced and are obviously
just air-dielectric coax without complete metal jacket around the hot
center conductor. These are open-wire lines by just about any defintion,
and are all unbalanced.
I wasn't especially advocating the system..that's why the "however"
followed. I do think it would be less lossy than an equivalent length of
poorly matched RG213, and the losses from radiation, whatever they might
be, would perhaps be of some use in making contacts. I know that the power
burned up inside the 213 won't contribute to the desired goal!
73
Ralph Matheny
K8RYU
207 Gibbons Place
Marietta Ohio 45750
mathenyr@marietta.edu
On Sun, 8 Feb 2009, K4SAV wrote:
> K8RYU wrote: "A couple comments. First off, the thing can be tuned from
> the shack with an "unbalanced openwire" feed, simply a wire carefully
> insulated from earth with, ideally, a number of parallel wires under it
> in or on the ground. Needless to say this will put a LOT of high
> voltage where people and pets might get hurt, but it will work and will
> not suffer the losses of a piece of RG-213."
>
>
> An UNBALANCED open wire feeder will radiate badly, and could have much
> more loss than a piece of RG213 depending on feeder length and frequency
> because it is close to the ground. Did you ever hear of a folded
> monopole antenna? It's just a quarter wavelength of unbalanced feeder,
> feeding a short circuit.
>
> Jerry, K4SAV
>
> Ralph Matheny wrote:
>> A couple comments. First off, the thing can be tuned from the shack with
>> an "unbalanced openwire" feed, simply a wire carefully insulated from
>> earth with, ideally, a number of parallel wires under it in or on the
>> ground. Needless to say this will put a LOT of high voltage where people
>> and pets might get hurt, but it will work and will not suffer the losses
>> of a piece of RG-213.
>> HOWEVER
>>
>> To run it on 160 and 80 seems require such a simple matching system that
>> I fail to see why one would do much else. A coil to ground, the size of
>> which will set the resonance of the vertical, with a tap on it which will
>> allow you to select the "50-ohm" point will get you all that the antenna
>> and ground that you have can do. You'd need to switch the coils and taps
>> to change bands, and perhaps even within the bands, but that all seems
>> very easy to do with little loss. The greatest problem will be dealing
>> with switching if really high power is involved, wien one might expect
>> 5-10KV on the base of the vertical.
>>
>> Why do they sell these things??? I don't know, but I bought one back in
>> 1960 while in high school. Then...it was called a "Gotham Vertical" and
>> I don't think I'll ever forget the "I've been had" feeling when the box
>> was opened and my $19 purchase consisted of 23 feet of aluminum tube,
>> 4 conduit clamps, and a piece of coil stock (not B & W). No magic box,
>> no free lunch, no nothin' special. But...I sure did learn a lot from that
>> vertical, and made a lot of contacts.
>>
>> Ralph Matheny
>> K8RYU
>> 207 Gibbons Place
>> Marietta Ohio 45750
>> mathenyr@marietta.edu
>>
>>
>>
>>
>
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