I believe a full wavelength loop is, in fact, a "quad," a single element
one.
And, I have stated before my real-life, factual, empirical observation of
yagis 8/8 Telrex and quad (4-element "Skylane"), during noisy conditions,
the quad was far quieter on receive.
I fully believe this to be the #1 advantage of full wavelength loops over
half wavelength antennas, not gain, mechanical strength, broadbandedness, or
other factors. Others clearly disagree and put the emphasis on these other
factors.
73 - Rich, KE3Q
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "RICHARD BOYD" <ke3q@msn.com>; "Tim Makins, EI8IC"
<contesting@eircom.net>
Cc: "towertalk reflector" <towertalk@contesting.com>
Sent: Monday, August 16, 2004 10:54 AM
Subject: Re: [TowerTalk] Horizontal Loops
> > Many people who have horizontal loops have them low, which
> is thought to be
> > good for a big signal close-in -- some of us have
> experienced having trouble
> > working close-in stations with antennas that are high --
> but a horizontal
> > loop that's at least a half wavelength up should work fine
> for DX, and I
> > expect will be "quieter" (less QRN reception) than other
> antennas, at least
> > in some conditions. 73 - Rich, KE3Q
> >
> > > So, if the loop is big enough, and has the right angles,
> it becomes a
> > > useful
> > > DX antenna ? The next question would have to be: How do
> you work out the
> > > required angles ?
>
> I replied to Tim but probably should have CC'ed the
> reflector.
>
> There are many myths about loops. One myth is they are more
> immune to QRN or noise, another is the peak gain from
> multiple lobe patterns is useful or effective gain.
>
> Whenever we see one thing touted as the answer for
> everything, we better lookout.
>
> Long loops can be forms of Echelon arrays if they have
> correct spacing and stagger, like the receiving array at
> http://www.w8ji.com/echelon-log_beverages.htm
>
> We also have to remember gain always comes at the expense of
> removing energy from some other angle or direction. The
> small multiple sharp lobes from a loop do not produce useful
> gain, because immediately next to each lobe is a deep null.
> Unless you can rotate the loop, statistically some desired
> signal is just as likely to fall in a null as on a lobe.
>
> With narrow lobe antennas that cannot be rotated, we have to
> plan the location of nulls or lobes or play roulette. The
> signal might fall in a 20 dB hole just as likely as on a 6dB
> peak.
>
> Noise is a myth. HF noise rejection comes from the pattern
> of an antenna, not the family of antenna. If an antenna
> responds better in the direction, polarization, and angle of
> a signal than at the accumulated noise from all other
> directions, it will be quieter. That generally requires the
> antenna have a very narrow clean lobe with a high ratio of
> gain in the desired direction to average gain in all other
> directions
>
> http://www.w8ji.com/receiving.htm explains this.
>
> I think the "low noise" myth is a carry over from quads.
> Yagi's have sharp pointed elements protruding which produce
> corona in inclement weather. The corona is at the high
> impedance tips, and impedance at that point somewhat matches
> the low-current high-voltage element discharge for maximum
> noise transfer. A quad generally has blunt sides at the high
> impedance point, and with well-insulated elements that are
> compact it has less corona. As a matter of fact, the quad
> was popularized from use at station HCJB where it was used
> to reduce corona!
>
> This noise difference in one special situation (hissing and
> sizzling corona noise in inclement weather) gets pushed
> along by myth and wive's tales to include general
> applications where it is a total non-issue, like power line
> noise or lightning storm QRN.
>
> The primary advantage of loops, Rhombics, and such is wide
> bandwidth and simple construction. The disadvantage is they
> occupy a lot of real estate for the amount of useful gain.
>
> 73 Tom
>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|