[CQ-Contest] 4-square dump power into horizontal dipole

RDStraw n6bv at arrl.net
Thu Apr 30 09:10:25 PDT 2009

Tor, N4OGW/5 said, refering a presentation I gave at Visalia 2009:

> There is a suggestion to run the dumped power from a hybrid-fed 4-square
into a (low) dipole rather than the usual dummy load. Has anyone tried that?
How did it work?

One evening about a dozen years ago, when I was still in Windham, New
Hampshire, my good friend Jack, W1WEF, and I got on 75 meters. Jack lives in
Glastonbury, CT, a distance of about 100 statute miles from Windham. Running
a kilowatt into his wire Four-Square array using a Comtek hybrid coupler,
Jack's signal in NH was about S9.

I knew that Jack had run the coax from the hybrid coupler's "dump power"
port to his shack so that he could monitor the Four Square by watching the
dump power level. As I recall, his dump power was less than 50 watts. At my
prodding, Jack connected a SPDT coax switch between the 50-ohm dummy load
and the coax from the Comtek box. Into the second port of the switch Jack
connected the coax from his 100-foot high 80-meter dipole, one leg of which
was tied to the same tower that supported the 80-meter Four Square. The
other leg of the dipole went to a tree. So the horizontally polarized dipole
was definitely close to the vertical Four-Square array.

What happened when Jack switched the dump power into the 100-foot high
dipole? His signal went up to S9+20 dB! He switched back and forth a number
of times and the results were always the same, a perfect demonstration of
what I'd call "free NVIS" coverage.

> I would be worried that a reactive termination would screw up the 4-sqr
pattern. And not to mention having another resonant antenna near the 4-sqr
verticals, even if cross-polarized.

DX stations in Europe that were monitoring our tests didn't detect any
change in Four Square's signal, but that's a pretty coarse measure,
considering that signals usually fade at least 10 dB on that New England to
Europe path, making exact gain measurements pretty iffy.

> I also have <1% dumped power at optimum on my 4-sqr, so it seems that it
really wouldn't add much high-angle fill-in?

You might be very surprised to see what 15 W (1% of 1500 W) can do into a
good horizontal dipole. It certainly makes local stations aware that you're
on frequency when they otherwise might not hear you well on the low-angle
Four Square, which has a deep null in the vertical-elevation pattern
directly overhead.

73, Dean, N6BV


Dean Straw, N6BV
n6bv at arrl.net

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