[TowerTalk] Delta loop

[n4kg@juno.com]

On Sat, 04 Nov 2000  Richard Thorne <rthorne@tcac.net> writes:

> I like the inverted delta loop, apex at the bottom and fed at this 
> point.

This is useful if you don't have room to stretch
a horizontal dipole but does take 2 supports.   N4KG

> This gives you both horizontal and vertical polarization.
> 

Actually, Polarization for that configuration is HORIZONTAL 
since the feed point is symmetrically placed on the horizontal axis.  

The vertically polarized currents are equal and opposite 
and therefore cancel out.  Effective height is between 
the top wire and the feedpoint.  If you can string a DIPOLE 
at the height of the top wire, it will have a lower angle of radiation.

The advantage of a conventional Delta Loop is that only a single
support is needed.  For horizontal polarization, the disadvantage
is that the effective height is below the support height.

Several years ago I built a 2L 40M horizontally polarized 
Delta Loop fixed at 60 degrees (EU, AF, Middle East) 
supported by a 20 ft boom at 120 ft.  The bottom wire
was at 80 ft. and fed in the middle for an effective height
between 90 and 100 ft.  It was a KILLER!

A reversible 2L Delta Loop can be realized by making 
2 equal length loops with 3/8 WL feedlines that are
switched (both conductors) by relays.  The open
stub provides an inductive reactance at the feedpoint,
loading that element to act as a reflector.

Another useful application of Delta Loops  on the low bands
where they can be fed 1/4 WL from the apex to achieve VERTICAL
polarization with an oval pattern that peaks broadside to the loop
and is roughly 3 dB down in the plane of the loop.  Feeding at 
the bottom corner results in mostly vertical polarization but with
some (high angle) horizontal polarization.

A 40M Delta Loop is just over 40 ft high.  An 80M loop 
is just over 80 ft high but can be stretched out to 
accomodate shorter supports.

de Tom  N4KG


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