|Subject:||Re: [TowerTalk] Delta Loop Info and Opinions?|
|From:||Joe Giacobello <firstname.lastname@example.org>|
|Date:||Thu, 04 Nov 2004 10:19:28 -0500|
Without going into a lot of detail, I wanted to share my evaluation of
delta loops for 30 and 40M. For some reason, probably because the same
formula (1005/f) is used to calculate the lengths of both quad driven
elements and delta loops and I knew that single quad loops had a small
amount of gain over a dipole, I thought their performance and behavior
were, more or less, identical. I now understand why Tom seemed to be
scratching his head over why I would want to install one, since I
already had a 40M EDZ. They are really different beasts. Even the gain
of quad loops deteriorates when brought relatively close to the ground,
as practical installations require for 30 and 40M (at least at this QTH).|
The delta loop is an extremely sensitive antenna. Its performance is significantly affected by its shape, ground quality, height above ground, feed point location, tilt angle and proximity to other conductive objects (i.e, towers). Its only advantage relative to a moderately high dipole, when it has been properly optimized, is low TOA and reduced high angle pattern. Even under the best of conditions, maximum gain is about 4 dBi, albeit at a pretty low angle. For instance, a 40M delta with its bottom wire 28 feet above good ground yields 4 dBi gain at a TOA of 15 degrees, while a 40M dipole at 85 feet above the same ground gives a maximum gain of 8.6 dBi at 23 degrees and 7.2 dBi at 15. However, the dipole does have a significant high angle lobe at this height (4.9 dBi at 90 degrees).
(I should point out that I only looked at deltas with height to base ratios of 1:3, which W4RNL said gave maximum gain. On the other hand, ON4UN says the equilaterals give more gain. I didn't check one vs the other.)
A lot of you folks probably already knew most of this, but it was a worthwhile learning experience for me.
The bottom line is I have reinstalled my 40M EDZ and just finished installing one for 30M.
73, Joe _______________________________________________
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.
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