> John Geiger wrote:
>
>> How high does a horizontal loop (the look skywire) need to be for
>> decent performance? A quick google search revealed that people
>> were running them at 25 or 30 feet with good results (in their
>> opinion). I know that high is better, but how high does it need to
>> be to show real improvement over a dipole?
>>
>> 73s John AA5JG
>>
Previous comments about height, and operating frequency were all
correct.
HOWEVER.... when a loop operates in two wavelength mode, or above, it
radiates
in the plane of the wire, not perpendicular to it. You'll find
this discussion in the
Quad Antenna Handbook, among other places.
A small digression, then back to the full wave loop...A 20 meter quad
element
is 2 wavelengths on 10 meters, for example. In quads which simply
tie three bands
loops together at the feedpoint, the 20m loop is still connected,
when operating on
10m. The result is 10m energy coming from the 20m loop, filling in
most of the 10m
nulls.
Similarly, a full wave loop on 160 is two wavelengths on 80. The
vertical angle of
radiation is quite low, (Cebik has modelled this.) and relatively
independent of height
above ground. That same loop on 40 is now 4 wavelengths. Similarly
low vertical angle
radiation, but now a directional pattern emerges, as nulls develop.
And so on, as you go up
in frequency. The more wavelengths you have, the more nulls you
have, but exactly the
same thing is true of a dipole.
Back on 160, the frequency where it's a full wave loop? It's like a
quad on its side. It's shooting
straight up. NVIS. And moving it a lot higher isn't going to
change that a great deal.
So, while a 2 lambda loop on 160 would be a very nice antenna for DX
purposes, (Probably quiet, too)
A one lambda loop would be perfectly appropriate for emcomm work
within a 500 mile radius.
In general, you will want to have whatever antenna you put up a
minimum of 1/4 wavelength above
ground, with 1/2 wavelength being better... and representing a
'modest' height. Note that that's
130 or 260 feet, in the case of 160! Even if you happen to have
four very cooperative 130' tall
trees to hang this beast from, you will have a 'low' antenna.
As you go up in frequency, things get better, of course. On 80,
where you now have a 2 lambda loop,
you'll get relatively low angle radiation, even at very low heights.
And to your question... what's "very low" ? 33' is 1/8 wave on
80... that's very low.
The practical answer to your question? Put the beast up as high as
you can manage, and
as much in the clear as you can manage, and get on the air! Real
antennas work better than
models, or opinions...mine own included. If it were me, I'd be
satisfied with 40-60'.
N2EA
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