Topband: Clipperton 2000

[k6se@juno.com]

Several subcribers inquired about the Delta 160-meter receiving antenna
used at FO0AAA.

It is a close relative of the Pennant and Flag antennas, which are
ground-independent relatives of the Ewe.  The Delta is a modification of
the "delta-shaped Ewe loop" shown in figure 7-66 on page 7-51 of ON4UN's
new Low-Band DXing book.

I took John's Delta-Ewe and, with the feedpoint and termination located
at the bottom corners of the triangle, I used EZNEC to optimize the
design for best F/B and zero reactance at 1.830 mHz.  This is the design
that was built by ON4UN for use by FO0AAA.

It is a delta loop-shaped antenna with a 28-foot (8.537m) bottom
horizontal wire and the apex 17 feet (5.183m) above the bottom wire. 
That means there is a total of about 72 feet (21.951m) of #14 AWG wire in
the triangular loop.

The EZNEC design had the bottom horizontal wire 3 feet (0.915m) above
ground, therefore the apex was 20 feet (6.096m) above ground.  It is a
ground-independent antenna, without the ground-related shortcomings of
the Ewe.

The termination resistor, which goes in one of the bottom corners of the
loop, is 950 ohms non-inductive.  The feedpoint is at the other bottom
corner and the feedpoint impedance is 950 ohms with zero reactance at
1.830 mHz.  An impedance matching transformer such as those previously
described on the Topband Reflector for use wiht the Pennant or Flag
should be used with the Delta antenna.

The F/B ratio in the EZNEC model is greater than 40 dB and the cardioid
pattern directivity of the antenna is in the direction of the feedpoint
end of the antenna (the same as with the Pennant, Flag, or Ewe).  The
gain of the antenna is about -34.5 dBi, so a receive preamp should be
used with the antenna.

The primary reason this design was chosen by the FO0AAA team was that it
was an easily-erected and easily-rotated directional receiving antenna. 
Only one support at the apex is needed (which must be non-metallic).  The
bottom corners of the antenna can be attached and pulled taut with rope
to tent stakes driven into the ground.  To change directions, it is a
simple matter to relocate the tent stakes to the desired direction and
re-attach the corners of the antenna.

Unfortunately, this design was done too late to make it into an article
about Flags and Pennants I wrote for QST (which will probably appear in
the July 2000 issue).

73, de Earl, K6SE

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