[TowerTalk] Delta Loop Info and Opinions?

[Joe Giacobello]

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