Delta RX Antenna used by FO0AAA
from Earl, K6SE on June 1, 2000
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 with 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