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From: Earl W Cunningham <k6se@juno.com>
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Hi, Topbanders,
With 160m DX season rapidly approaching us in the northern hemisphere and
AF4OD's query about Beverages, I thought I'd share my little Beverage
knowledge with you.
All I've ever used are single-wire unidirectional Beverages from one to
two wavelengths long, and here's how I recommend their configuration
based on my experience:
I use a 5-foot ground rod at each end of the wire. A ten-foot length of
3/4" copper tubing can be purchased at the hardware outlet for about US
$3.00 and then cut in two equal 5-foot pieces which are easily driven
into the ground.
Use electric fence wire for the antenna. This steel wire (usually
galvanized) will outperform the same Beverage made of copper wire. I
once replaced a 1100-foot steel wire Beverage I had with copper. I
expected better results than the super performance of the steel wire
Beverage, however I was greatly disappointed. I quickly took down the
copper and put the steel wire back up.
Puzzled why the steel wire so noticeably outperformed the copper, I
thought about this a bit and came up with what I believe is the reason.
A Beverage is actually a bidirectional antenna, however we all try to
attenuate the signal coming from the unwanted direction by terminating
the wire with a resistance to ground at one end to absorb the unwanted
signal. This is what gives the Beverage such a good F/B ratio and
therefore a good S/N ratio. But not all of the signal from the unwanted
direction is absorbed by the termination resistor -- some of it is
reflected back down the wire toward the receiver, hence limiting the F/B
ration and the S/N of the antenna.
The answer appears to be simple: The unwanted signal has to travel down
that lossy steel wire twice, but the desired signal travels down the wire
only once. This is what makes the steel wire perform better than copper
wire -- the greater attenuation of the undesired signal results in a
better F/B ratio.
Electric fence wire is significantly less expensive than copper also, and
it is stronger. If you plan switchable (two direction) Beverages, then
definitely use copper wire.
In my most recent temporary Beverage (used to snag VK9YY last winter)
which was a 550-footer, I wound a simple matching transformer using an
Amidon FT140-43 toroid core with a 12-turn winding on it. One end of the
winding went to ground at the feedpoint and the other end went to the
Beverage wire. The coax center conductor was tapped onto the winding
four turns up from ground for 50-ohm coax. If you use 75-ohm coax, tap
at five turns up from ground. This transformer was easy to make and
worked well. No preamp was needed to boost the signal at my receiver.
When I worked VK9YY, he was unheard on my tx vertical array and 559 on
the Beverage.
The correct termination resistance over my Mojave Desert soil is 330
ohms. This was determined by walking the wire with a field strength
meter a la original article by H.H. Beverage in December 1921 (or was it
1922?) QST.
One additional point -- I've found that one radial at the terminated end
of the wire enhances performance. I just lay about 125' of the same
electric fence wire on the ground, one end connected to the 5-foot ground
rod and the other end running in the direction of the desired signals.
No radials have been used at the feedpoint end, although that may help,
too.
I like a height of about 7 feet for my Beverages -- just high enough so
that no human of normal stature can hang himself on the wire ;-)
73, de Earl, K6SE
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