I have been following the recent threads on reversible Beverages
made from WD-1A wire with interest. Results with this type of
construction seem to vary, for reasons yet unknown. I thought I
would take a few moments to summarize my experience with WD-1A
Beverages. My new Beverage "farm" consists of four such Beverages.
They range in length from approximately 500 to 650 feet. I am using
home wound transformers with BN-73-202 binocular cores, as described
by Tomi, OH2BEN. Direction switching is by means of a relay at the
feed point, powered via the coaxial cable.
With regard to gain, my experience has been typical of what has been
reported by others: gain is about 6 to 8 dB lower in the "reverse"
direction. This is somewhat annoying, since I prefer to keep the
signal level about the same on all antennas I use for listening (it
helps maintain optimum S/N ratio without the need to adjust preamp
gain or attenuators). However, the lower gain in the reverse
direction is not a serious problem as long as the pattern remains
acceptable.
Front-to-back ratio has a tendency to be very good in the "reverse"
direction but not as good in the forward direction. A poor ground at
the far (non-feed) end seems to make this worse but even with good
to excellent grounds I still notice some difference in F/B between
the two directions. This may be unique to my particular
installation. All of my Beverages run over uneven terrain and have
some vertical slope somewhere along their length. I theorize this
may result in a different pattern for the two directions. Other
theories include imbalance in the reflection transformers or the
Beverage itself. I am very interested in the experience of others
with regard to F/B of WD-1A reversible Beverages.
Two of my Beverages are "center fed" (actually fed at some
convenient arbitrary point) while the others are end fed. I have
come to prefer feeding somewhere near center when it is practical to
do so. Center feed equalizes gain between the two directions, with
gain for both directions being 3 to 5 dB down in comparison to the
forward direction of an end fed Beverage. F/B with center feed seems
about the same in both directions, but not as good as in the reverse
direction with end feed.
Overall I feel the WD-1A Beverages are hearing well. I am not able
to have conventional single-wire Beverages up at the same time to do
direct A/B comparison. Having had conventional Beverages for several
years, my perception is the WD-1A Beverages work nearly as well with
the exception of somewhat poorer F/B in the forward direction.
Ladder line or relatively wide spaced wires would probably work
better for reversible Beverages, at least in terms of equalizing
gain between the two directions in the end fed configuration.
However, either type would be very much more difficult to work with
in my situation, running over uneven terrain which slopes in every
direction and through dense forest. WD-1A wire is as easy to work
with and keep in the air as a single wire.
On a final note, I have tried to prevent the WD-1A wire from
breaking when (not if!) trees fall on it. At each end point there is
an insulator, followed by a few inches of 18 AWG solid insulated
soft copper wire attached to the end support post (aka tree). This
wire is much weaker than WD-1A and will break with much less tension
than the Beverage itself. The feed or reflection transformer box is
separately attached to the tree, and 1/4" blade quick disconnects
(known as faston connectors in EU I believe) are used in the
pigtails of WD-1A going to the box. This provides a "break-away" end
connection. All intermediate insulators along the Beverages are of a
type that allows the wire to slide through with very little
friction. This strain relief has been tested once so far, and it
worked. Repair took 10 minutes, mostly walking time, and required
only a saw (to cut the downed tree, thus freeing the wire from under
it), ladder (to reach the Beverage termination box), and 12 inches
of the #18 copper wire. More tests may be imminent, as the wind is
really howling today!
73,
Paul N1BUG
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