[TowerTalk] delta loop beams - how to feed.

[n4kg@juno.com]

I'll take a stab at answering your question about gamma match
feed of an upside down Delta Loop.

The Gamma Match is an unsymmetrical feed that presumably
results in a near symmetrical current about the center (bottom
corner) of the Delta Loop due to the tight coupling of the continuous
loop, similar to the near symmetrical current distribution in a
Yagi Driven Element.  

In the case of the upside down Delta Loop, the near symmetrical
current centered at the bottom corner results in horizontal polarization
due to the cancellation of the opposite vertical components and 
enhancement due to the addition of the horizontal components.
(Yes, a  picture helps.  Draw the current vectors parallel to the
tubing).

Tom  N4KG

On Tue, 18 Sep 2001 "Tim Makins,  EI8IC" <ei8ic@eircom.net> writes:
> 
> Hi Henry and others - I'd be interested to know where and how this 
> antenna
> was fed. According to the books I've seen, an upside-down delta loop 
> needs
> to be fed in one of the top corners for long distance working, but I 
> can't
> see how you can do this without the feedline interfering with the 
> element.
> When you say 'Each band was fed with separate feedlines through 
> gamma matchs
> affixed to the boom', that implies that it was fed where the two 
> aluminium
> tubes met the boom, which my book says has a radiation angle of 
> 47deg.
> 
> 73s Tim EI8IC
> 
> ----- Original Message -----
> From: <K4tmc@aol.com>
> > The antenna you are inquiring about was the model DL-TRI by Delta 
> Loop
> > Antenna, Inc. of Weston, VT (previously in New Milford, CT).  The 
> company
> is
> > no longer in business.  The owner, Robert Hobert, KA1UJ is, I 
> think, a SK.
> > The array is very strong, using none of the standard U-bolt type 
> clamps.
> > Element-to-boom and boom-to-mast joints are all done with 
> heavy-duty solid
> > machined aluminum parts, not castings, and stainless steel 
> hardware.  Two
> of
> > the 3 sides were made of aluminum tubing that rose from the boom 
> at an
> angle
> > with a copper wire stretched across the top for the 3rd side of 
> the delta
> > loop.
> >
> > I purchased what may be one of the last DL-TRI's back in April 
> 1993, when
> he
> > was not actively building any arrays with 10 Meter capability due 
> to the
> low
> > sunspot activity at that time.  The array included 2 elements on 
> 20 and 15
> > meters plus 3 elements on 10 meters and weighed 81 lbs when fully
> assembled
> > on a 13.5 ft boom.  Each band was fed with separate feedlines 
> through
> gamma
> > matchs affixed to the boom.  There was a review of the DL-TRI in 
> CQ in
> June
> > 1988 by Lew McCoy, W1ICP.
> 
> 
> 
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