Worked on tower/antennas on North Caicos Feb 9-19... tower is up! This
tower is 20.5 inches per side with 1.5 inch pipe for each leg. Each piece
is 10 ft and terminated with a flat plate with 3 bolts per leg... I found
it as a "surplus" tower from the recent improvements to the airport on
Provo. It is combination welded/bolted configuration. Anyone want to
venture the manufacturer??? I have two thrust bearings ( one at the top
and the second approximately 3 ft down). Rotor shelf is 2 ft below the
bottom thrust bearing.
Antenna construction: XM-40 Hy-gain took most of a day to assemble. I did
not use the balun supplied but elected to do a 11 turn coil of RG-213 as a
"choke". The XM-40 will be 12 ft above the top of the tower and a very
inconvenient place to change a balun.
Resonance is 7.080 with a near perfect SWR... 1.6:1 at bottom and 2:1 at
7300...on the air results were EXCELLENT!
The Bencher SkyHawk was assembled the second day. I have assembled many
antennas and suggest that Bencher needs to reconsider their instruction
manual!!!!!
Boom assembly could be greatly enhanced by marking the many sections of
boom material at the factory ( KLM has done this for years)!
I was given advice from VE3RM and others that the supplied balun should be
discarded.... after opening it up I saw why! If you buy the antenna throw
the balun away unless you strictly do QRP!!! A second warning is that the
20M driven element is tightly coupled to the 10M and 15M driven element
without actual mechanical connections... this match changes with the
element spacing and is greatly influenced with WINDY conditions. I first
put the antenna up with no changes in the driven element arrangement... SWR
was all over the place ranging from 1.1:1 to 1.8:1 on the same frequency
just depending on how the wind was blowing... this has to be totally
unacceptable!!! I have solved the trouble temporarily by attaching 2 3/8"
PVC rods on each side of the driven element... the rods are held in place
with plastic wire ties. After this change SWR is constant regardless of
windy conditions. The SWR on 20 and 10 is under 1.3 :1 across the whole
band... on 15 it ranges from 1.6:1 at 21000 to 1.4 :1 at 21.400 (
resonance 21.150 is near perfect). On the air testing of the antenna was
EXCELLENT.
I will be back down on April 3 installing a mast to make all the stuff turn
as well as putting together the 80M-1 dipole by M2... thanks to all on
towertalk for the help and advice...
Looks like a decent contest station is going together on North Caicos.
73
Bud, K4ISV
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