I came in late on this thread, so I don't know whether Rick is talking about
horizontal or vertical loops. In either case, I think there's a reasonable
explanation for the observation that loops outperform dipoles in Field Day.
My club has had the same experience in Field Day, namely that loops
outperform dipoles. However, we use *horizontal* loops, which are well-known
to be cloud warmers. The reason they are so effective for us in Field Day is
that the signal arrival angle from large numbers of nearby (East Coast)
domestic US stations is quite high. A good dipole, at least 1/2-wave high,
has a much lower angle of radiation than a horizontal loop, and would be
more appropriate for a DX contest.
If Rick is saying that *vertical* loops outperform dipoles in Field Day,
then the most likely explanation is that the dipoles are not high enough.
For example, an 80m dipole up only 65 feet (1/4-wave) will have reduced
directivity -- i.e., it's going to be more omnidirectional than
bidirectional. A dipole should be up at least 1/2-wave to get optimum
bidirectional performance. In contrast, a delta loop on 80m can provide
excellent broadside directivity (bidirectional) with the apex up about 70-75
feet and the bottom wire 10 feet off the ground.
73, Dick WC1M
> -----Original Message-----
> From: Sinisa Hristov [mailto:shristov@ptt.yu]
> Sent: Sunday, March 14, 2004 7:17 PM
> To: tentec@contesting.com
> Subject: Re: [TenTec] 80M LOOP
>
>
> Rick Westerman wrote:
>
>
> > I stand by my statement that at all the clubs I've belonged to, the
> > loop has outperformed the dipole for the type of operations
> needed for
> > Field Day contests. That of course means to work as many portable
> > stations as possible, the majority of whom are in the same
> country (DL
> > in my case). I'm not talking about one dipole that didn't
> perform -
> > I'm talking about many dipoles that didn't perform.
> Actually they did
> > perform but the loop simply performed better. The 80/40 meter
> > difference was small and sometimes the dipole was equal, but it was
> > almost never stronger. Usually the loop was stronger. On
> the higher
> > bands, the loop stomped the dipole.
>
>
> Did you investigate WHY?
>
> Antenna A (as sophisticated as it can be)
> can outperform antenna B (as UNsophisticated as it can be)
> in ALL directions (both azimuth and elevation),
> ONLY if antenna B has too much loss,
> i.e. transforms most of RF energy into the heat instead of waves.
>
> All 100 % efficient antennas have exactly the same AVERAGE
> "gain", i.e. there is no such thing as "gain" per se - what
> the word actually describes is simply focussing of radiation.
>
> This means that antenna A can produce a few dBs more
> in a selected direction ONLY by producing
> several dBs less in ALL the other directions.
>
> In essence, that is the law of conservation of energy.
> And I don't think you'd claim encountering a perpetuum mobile.
>
> Properly constructed antennas have almost perfect efficiency,
> with loss on the order of 0.1 dB or less.
>
> Therefore, if your loops were always better than dipoles,
> then the dipoles were bad, very bad, plain and simple.
>
> Can we agree on this before proceeding any further?
>
>
> > I could buy into your theory if this had only happened once
> or twice.
> > But it happened many, many times.
>
> Obviously a bad method of dipole construction
> did not become a good one by pure repetition.
>
>
> > All of these articles and my experience with it (which spans 25
> > years) point towards this antenna out-performing a dipole - but I
> > couldn't tell you why!
>
> That's a very convenient and powerful method :-)
>
> But it has a minor problem of not being scientific.
> And although we are not scientists, that doesn't enable
> our antennas to work better than the laws of nature permit.
>
>
> 73,
>
> Sinisa YT1NT, VA3TTN
>
>
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