TopBand: Interlaced Delta Loops

[Earl W Cunningham]

Reflectees:

Carl, KM1H asked what interlaced delta loops might look like using EZNEC.
 I sent him the following info and he requested that I share it with
others.  Here it is:

First, I modeled a single equilateral triangle delta loop with its bottom
wire 8' above "good" earth.  To resonate at 1.830 mHz, each side had to
be 181.6' long, or a total of 544.8' of #12 wire.  The feedpoint was
adjusted for max vertical radiation -- this turned out to be 25% up from
the bottom of either side wire.  At resonance, the feedpoint resistance
was 204 ohms.  The azimuth pattern was oval, with max radiation of 1.8
dBI perpendicular to the plane of the loop at a TOA of 21 degrees.

I then "built" a second identical delta loop at right angles to the first
one, with their apexes at the same point.  To keep the wires from
touching, I lowered one loop to 7.5' high and raised the other to 8.5'
high.  Feeding power only to one of the loops resulted in a near-circular
(within 1 dB) azimuth pattern -- considerable coupling to the unfed loop.
 Gain was 1.2 dBI @ 21 degrees -- about the same as a 1/4-wave vertical
over the same soil.  The unfed loop had perfect current distribution for
vertical radiation.  Feedpoint impedence of the driven loop was about 300
+ (-?) j300, as I recall.

I then fed both loops in phase.  The pattern was close to the same as the
last case, just a bit more circular -- within about 0.75 dB.  Resonance
of both loops shifted up *considerably* in frequency -- I had to add
about 16' to each side of the loops to bring them back to 1.830 mHZ! 
After resonating the loops their feedpoint resistances were about 400
ohms each -- double that of a single loop. Gain was about 1.15 dBi @ 21
degrees, again about the same as a full-size vertical.

I then fed the two loops 90 degrees out of phase.  The pattern became
slightly unidirectional (about 1 dB F/B) and little gain change was
noticed.  Feedpoint impedances were the most affected and were
unbalanced.

I then fed the loops 180 degrees out of phase.  This resulted in 4-leaf
clover-like azimuth pattern, with about -2 dbi gain in the favored
directions.  Resonance of both loops shifted far downward in frequency --
I didn't bother to adjust the loop dimensions to get them back into
resonance.

Feeding them 45 degrees out of phase was little different than zero or
90-degree phasing.

Feeding them 135 out of phase resulted in a pattern somewhat between 90
and 180-degree phasing.

All in all, best results were obtained feeding both loops in phase, which
had a pattern and gain similar to a vertical with a good radial system. 
An advantage that immediately comes to mind is that with the interlaced
loops, no radials are required.  A possible disadvantage is that a
support almost 170' high is required.
TOA is about 3 degrees lower than a vertical over the same "good" ground.
=====================
Carl commented that interlaced delta loops for 80m would be more feasible
because a support of about 80' or 90' would be needed.  I suppose the
loops could be "flattened" somewhat (longer bottom wire, shorter side
wires) to enable using a shorter support structure.

73, de Earl, K6SE


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