Here are a few Ewe, Flag, and Pennant questions
for antenna-modelling program experts.
(1) Ken Alexander did some Pennant optimizations
for medium-wave (AM broadcast) use. He came up
with a vertical-section height of 16.4 ft., slanting
members lengths of 54.6 ft. each (for a horizontal
length of 52.1 ft.). By comparison, the standard
Pennant dimensions (as developed by K6SE for 160 m
use) are 14 ft. vertical, 30 ft. slanting members,
29 ft. horizontal length. If a medium-wave Flag
was built, would a 16.4 by 52.1 ft. one have any
advantage in front-to-back ratio over one with
dimensions of 14 by 29 ft. ? Obviously it would
have more signal output, but it's directivity
that usually matters most.
(2) Deltas (including Neil Kazaross's squashed-
delta) are fed at one of the lower corners and
terminated at the other. How would a Flag shaped
antenna fed and terminated at lower corners do
compared to a conventional Flag fed and terminated
halfway up its vertical sides ? This would be
like a Ewe with a wire connecting across the bottom
instead of using ground rods at each end. Is
this a workable design if the bottom wire is, let's
say, about 5 ft. off the ground ? Would it be as
ground-independent as a regular Flag ? How about
immunity to pattern influence by nearby antennas
and metal objects: better, worse, or same as a
regular Flag ? Conventional Ewes have dimensions
(vertical height, horizontal length) of 10 by 27 ft.
for the 80/160 m model and 15 by 38 ft. for the
160 m optimized model (this would presumably also
be good at medium wave). Bruce Conti in NH is using
a 50 by 75 ft. Ewe with good medium wave results.
It seems to work a bit better when the bottom wire
scheme is used in addition to, or in place of, the
two ground rods. That ratio seems too lopsided in
favor of the vertical sides, especially considering
that Neil's "Kaz antenna" (delta) has a 1 to 4 height
to base length ratio instead of 1 to 1.5. The Koontz
Ewe ratios in the 1 to 2.6 range and the Cunningham
Flag ratio of 1 to 2.1 seem to be the happy medium
values here. The Ewe-Flag hybrid (groundless Ewe) -
if it works - may have its best performance around
a 1 to 2.4 ratio such as 20 ft. side height by 48 ft.
base and top length for a decent medium wave and
160 m set-up. Ideas ?
(3) I have done some initial tests that indicate that
feeding both ends of a Pennant, Flag, or Kaz delta
through 16:1 transformers (Mini-Circuits T16-6T or
a d-i-y equivalent) effectively loads each end with
800 ohms and gets you reasonably good front-to-back
ratio when you switch from one coaxial feedline to
the other. W7IUV amps can be used on these lines in
the "shack" or out in the same boxes as the transformers
with not too much difference in signal-to-noise ratio.
The front-to-back may be slightly less than could be
had by feeding only one end and precisely terminating
the other, but the two-feedlines scheme actually gets
you superior nulling when the two feedlines are presented
to the inputs of a phasing unit such as an MFJ-1026,
Quantum Phaser, or homebrew model. 30 dB may be close
to best-case cardioid null with a standard Flag or
Pennant. The dual feedline version with phasing unit
can easily do 40-50 dB of null on groundwave and often
30 dB on skip. Two phased quarter-wave spaced Ewes or
Flags can probably beat this, but they won't fit in the
typical small to medium urban / suburban backyard either.
Any comments on the above questiona and discussions
will be appreciated.
Mark Connelly, WA1ION - Billerica, MA, USA
and
RF Circuits Page: http://www.qsl.net/wa1ion/index.html
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