> In short, I'm trying to determine if any Loop configuration offers a real
> advantage over a high >1/2 wave Dipole. Again, I know what the models
> say....what was/is your actual experience, >please?
For gain vs. height stuff, I'd rely more on the models, honestly.
The models really tell you what you need to know. Why? Because the
differences in ground clutter, soil conditions, noise sources,
available supports and whatever else at other people's stations don't
affect yours at all, while at your station they're held *more*
constant at least. So model comparisons of the two antennas will
probably do a pretty good job at telling you how the two antennas
would work at various elevation and azimuth angles... something that
you'd need a lot of free time and probably a helicopter to answer with
measurements.
I could give you a *very* misleading real-world answer about a 10m
slightly more than full wave loop (actually 12m loop fed with a
matching network) and a 10m flattop dipole (actually a 10/15 trap
dipole) at about 80% of the *top* height of the rectangular loop.
That misleading answer would be this: the two antennas have the same
gain but the loop has quite a bit better signal to noise ratio.
This is true on both 10 and 15 ... it's actually so dramatic on 15
that I worry the antenna is broken... until I listen to the same
signal on both. Same strength, better copy on the loop. Some will
say "aha! proof that loops are quieter!"
In practice, at my house, this is true. In theory, it's largely
nonsense, the noise part anyway. The gain part pretty much jives with
models... they should be pretty much the same at those heights.
The noise part doesn't actually have anything to do with which antenna
is which; it's a location and construction thing. The loop is much
further from the noisy house, and further from my big vertical which
tends to be a good reradiator of noise. The dipole is strung
between the vertical and the house. The loop is probably also choked
better and certainly installed more symmetrically with respect to its
surroundings.
http://n3ox.net/pictures/12loop_lg.jpg < -- the loop
http://n3ox.net/pictures/backyard_lg.jpg < -- the dipole, etc
So does the loop have advantages? Well, for me it did. After all, I
bothered to build the thing ;-) There was no way to build a
horizontal rotatable flattop dipole for 12m using just the support
pole I used for the loop and have it be at a height that gave the
dipole a gain advantage. The loop is narrow, just 7 feet wide or so,
I believe.
The loop's feedpoint is quite low on the pole compared to a
dipole/doublet that would be similar. That let me hang some extra
weight off the pole at the feedpoint in the form of relay switched
matching networks for 10m and 15m. So now I have a decent rotatable
triband antenna.
The models told me a dipole and a loop that I have installed here have
very similar gain, and that's what I found in the real world, and both
are such simple antennas that I think the models give you the clearest
picture of how that works. If you get someone that says "I had a
flattop dipole for 40m at 70 feet and a quad loop with the top at 85
feet and the quad loop was 15dB stronger than the dipole" then you
should suspect that person of not knowing how to build a dipole or
getting their amplifier confused with their antenna switch ;-)
73
Dan
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