[Top] [All Lists]

[TowerTalk] Result - 40M wire beam (long)

To: <>
Subject: [TowerTalk] Result - 40M wire beam (long)
From: (Richard L. King)
Date: Mon, 08 Dec 1997 16:05:50
I have been thinking for a week about what I will say about this antenna
and here it is:


Before the 1997 CQWW CW I had noticed that two of my new towers were in
line to Japan. The towers were 66 feet high and spaced about 150 feet
apart. Since, I don't have a 40M beam up yet, the thought occurred that a
wire beam might be helpful during the contest.

I put a request for more information about wire beams on the Tower Talk
reflector and got two major repsonses. The first was from Jon, N5JA, who
used the YO program to design a system for me. The measurements, in inches,
for that antenna are:

Element    Location    Half-Length
=======    ========    ===========
 REFL          0.00      422.00
 DRIV        221.75      413.00
 DIR1        376.25      393.25
 DIR2        638.50      383.50
 DIR3        930.50      392.00
 DIR4       1300.00      382.00

And here are the gain figures:

Takeoff    Dipole    Beam     Difference    3-dB Beam-
 Angle     (dBi)     (dBi)    in Gain dB    width (deg)
=======    ======    =====    ==========    ===========
  40        6.11     11.07       4.96           58
  35        6.27     12.11       5.84           60
  30        6.11     12.65       6.54           60
  25        5.55     12.62       7.07           60
  20        4.47     11.96       7.49           60
  15        2.67     10.45       7.78           60
  10       -0.34      7.65       7.99           62
   5       -6.02      2.08       8.10           66

Then I got a response from Dennis, K5YA, with measurements he developed
using the AO program. Those measurements, in feet, are:

sr = 0
sde = 30.75845
sd1 = 48.52695
sd2 = 82.60276
sd3 = 127.1066
sd4 = 140.3137

ref = 35.03213
de = 34.15941
d1 = 33.67949
d2 = 33.60951
d3 = 33.42221
d4 = 28.0213

With these gain figures:

6 ele  11.75 dBd at 24 deg, f/b=11.9

Until now, neither Jon or Dennis knew which set of figures I used. I
literally flipped a coin and it (the coin) decided that I would use Jon's
figures. I am not sure how much difference there will be between these two
antennas. The elements are very close but the spacings were quite
different. It is obvious to me (I am not a antenna software design person)
that the design of a yagi or any other antenna from software isn't very
straightforward with its results.

Building the antenna:

I had a lot of #12 wire from 160M and 80M loops that I used to have up in
New York. So Susan (K5DU) started measuring and cutting pieces of wire for
the elements. For the driven element, I used one of the little dipole
center insulators with a SO238 installed and a little hole at the top of
the assembly to tie a support rope; the kind of center insulator you can
buy at any hamfest.

Then I went to my junk box and found some little flat pieces of plastic
about one inch wide and 4 inches long. I drilled a hole in each end of
these plastic pieces. Then I stripped a couple of inches in the center of
the reflector and director element wires, put the wire through one hole of
a plastic piece, made a twist in the wire, and soldered it so it wouldn't
untwist. Then I installed a small snap clamp in the hole in the other end
of each of the plastic pieces.

Susan and I got a 300 foot length of 1/4 inch nylon rope for the boom and
installed it with pulleys between the two towers. Then we started measuring
the element positions along the boom rope. We started with the reflector
and made a knot in the nylon rope where we wanted it to be. We made the
knot so that a small loop of rope would hang down and we double knotted it
so that the knot would not pull out with tension. Then we measured to the
driven element position, made another knot, and then on to the other elements.

On each element, we used lightweight end insulators and string. For the
anchors on each element, we used small, steel, pound-in 4-foot electric
fence posts (12 total). Then we added a piece of RG8X coax to the feed
point that was just long enough to reach the ground. At that point we
connected it to heavier coax to run the 300 feet to the hamshack. Then we
used the snaps on each element center to attach to the rope loops.

Finally Susan and I pulled the system up and tried to center it between the
two towers. It was a hard pull since all those elements added up to a bit
of weight in spite of our efforts to keep the weight down. Next we
eyesighted the element positions and drove in the element end-anchors about
70 feet out from the center of the boom. Then we tied everything off
loosely because we didn't want to put extra downward pressure on the rope
boom. In spite of this, the boom still formed a definite U shape that got
worse with time and weather. Something like Phillystran would make a better
boom and would pull tighter. But our towers are guyed at 36 feet and there
are no guys at the 66 foot level yet and we didn't want to pull too hard.

Results from the contest:

Since the 6 element wire beam was pointed towards Japan, it didnt see much
use until the band opened that way. The first night I seemed to run ran JAs
very well. I felt loud and any mult in that direction was easy to work. The
second night I worked more JAs but the band didn't seem to be as good as
the first night. At that time, I really felt that the antenna was a success.

I managed to work about 236 JA stations and 14 other Asia stations with the
antenna during the contest. I felt pretty good about that until I check
with my local competition, K5YA. Dennis had 441 JA with 40 Asia stations
during the same contest. He really whipped me on 40 meters good. Dennis has
a 2 element rotatable yagi up in the air a good distance.

So maybe I didn't do so well, after all, with the antenna. The judge may
still be out as to its effectiveness. But I felt the wire yagi was better
than any 40M dipole or sloper that I already had up in the air here.
Perhaps it will never be as good as a rotatable 40M yagi with good height.
Dennis and I may do some follow-up comparsions when we both have time to
get up in the morning. 

If I don't get a 40M rotatable beam up before the ARRL DX Contests, I might
try Dennis's measurements and put another one of the antennas up pointed at
Europe. Whether I do that may depend of further observations of the first
wire beam.

Antenna expermentation is fun.

73, Richard


FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>