Mike and Don,
I have been using an expanded version of a DHDL here since November 2011. I was
forced into going this way because the neighborhood around me has become very
noisy and the antenna seems to be less susceptible to noise than my other
antennas. I call it the Dual Flag array. I essentially expanded the DHDL deltas
into the shape of a flag. My flags are large, approximately 24.5 feet tall and
32.5 feet long and separated by three feet. The wires cross in the middle
rather than at the bottom so the flags are 180 degrees out of phase. They are
similar to a Waller Flag antenna in some respects.
My dual flag antenna is supported in the middle by a 31 foot pole made up of
military fiberglas poles and the ends are supported by two trees. The bottom
wire is 6 feet above ground. The feed transformer was wound on a binocular core
with two turns on the primary and 7 turns secondary giving 918 ohms when fed
with 75 ohm cable. I think my load resistor is 1290 ohms at the back of the
second flag. You can put a variable pot there and tune for best F/B but that is
not necessarily the best RDF.
I have found my dual flag array to be the quietest RX antenna in my RX system.
It works very well on 160 through 40 although the pattern turns broadside on 40
meters. It beats all my 450 foot beverages hands down and is a great compliment
to my HiZ 4 square which is now on the main RX of the K3 with the dual flag on
the sub RX. You can also build a switching system to reverse directions but the
circuit is rather complicated so I have two of these dual flag antennas pointed
in different directions. I manually switch directions by moving the
transformers and loads around using banana jacks when really need to grab a new
country.
As with all antennas of this type, an effective common mode choke at the feed
point is an absolute must.SInce a rotatable version would be very difficult to
build and support on a tower, the next logical step would be a smaller true
Waller Flag like NX4D's Big Waller.
I must give credit to George AA7JV who modeled this antenna for me and provided
the inspiration through his TX3A DHDL RX antenna.
73, Dennis W0JX
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