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Flag
antenna report
By George Maroti
Topband mail list, November 25, 1999
My flag was built to the exact dimensions specified by Earl K6SE,
(14 feet high by 29 feet long, mounted 6 feet above ground). I used
a 950 termination resistor. For the impedance matching transformer
I used an FT114-43 toroid, with 35 turns of #24 insulated solid
copper (telephone) wire to the antenna, and 10 turns of #24 to the
coax (75 ohm RG-59/U).
My QTH is Mount Kisco, approximately 40 miles North of New
York City.
For my first test, the flag was oriented to receive signals from
the N-NW, at an approximate 330 degree bearing. During my local
morning (1300 UTC) on the MW band, and in comparison to my dipole
and T2FD antennas, the results were as follows:
1. Several times the flag heard stations which were completely
inaudible on the other antennas.
2. I was able to almost completely null WLUX 540 kHz 60
miles to the South-South East. This station was about S6 on my Drake
R8B with a 30 meter dipole, and only S1 with the flag.
3. On frequencies with 2 stations audible, the flag was
able to either null one of the stations, or bring the station that
was in the background out in front.
Tests were also conducted with the feedpoint and termination
reversed, essentially at a 150 degree bearing. This time during
my local evening (2300 UTC), I was able to receive stations in Cuba,
Columbia, Venezuela and St. Kitts. Although these are not considered
tough DX catches by MW DXers, the quantity of these stations as
received by the flag far exceeded my other antennas.
I'm convinced that my flag is performing as a directional antenna
on MW frequencies. At SW frequencies however, my results are quite
different and disappointing. My main interest was to use this antenna
for the 90 and 60 meter tropical bands. At these frequencies however,
the antenna was quite deaf. Above 6 MHz, gain returned somewhat,
but directionality was lost. Gain was not equal to the dipoles or
T2FD, but the flag could be used up to 20 MHz or so.
I realize the flag and pennant were optimized for 160 meters;
perhaps those with modeling software can determine what the optimum
dimensions should be for the tropical bands. I'm considering replacing
the fixed 950 ohm resistor with a Vactrol to see what effect varying
the termination resistor has.
Finally, this was my first attempt at winding an impedance matching
transformer, so I'd like some reassurance that I did this right.
I wound the 35 turns on one side of the toroid, and the 10 turns
on the opposite side of the toroid. I believe this was suggested
by others, but it is not consistent with previous designs I've seen.
I'm used to seeing the larger (primary) winding covering the entire
diameter of the toroid, with the smaller winding wound over the
primary. |
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