Back in the fall I purchased a used TH-7 and completly dismantled and
reassembled the antenna before putting it on the tower in late October just
before CQWW. My procedure and subsequent findings are as follows.
All tubing ends were cleaned with 000 steelwool. (I have never experinced
rust particles using steel wool as long as the particles are wiped clean
from the tubing.) I compltely disassembled all the traps. I used 7/8 inch
tubing to push the insulators and thus the coils from out of the capacitor
tubes. I made sure the windings of the coils were clean and I tightened the
screw connections to the tubing. Make note that the 15 meter coil traps
ONLY on the driven elements are of copper wire while all other coils
throughout the antenna are aluminum. The copper wire is soldered to a lug
and then screwed down to the tubing. I found one cold solder joint that
coincided with the previous owners problem of high SWR on 15 meters. I
heated and resoldered all lugs on the copper coils. I replaced the plated
screw that holds the capacitor tubing of the traps to the element with
stainless steel screws. I reassembled the entire antenna and cleaned all
connections with light sandpaper or steel wool. I used a very light coating
of penetrox, just enough to leave a thin film. I used the DX settings as
suggested by Roger Cox. The antenna was place at 60 feet and is fed with
1/2 Andrew heliax. It perfoms as advertised. SWR curves fall exactly as
the manual shows, and it plays fairly well for a tri-bander. I would have
replaced the BN86 balun with a home brew high power one wound on a number 61
core, but I was in a race against the oncoming winter weather and let it be.
I have had no problems running 1500 on all three bands.
A note about the copper coils for 15 meters. Yes, they do exhibit a higher
Q than the aluminum ones. I do not know why Hy-Gain uses them on 15 and no
where else. A need for more efficiency on 15? I don't know. However, copper
throughout the antenna would add extra weight and cost.
Bill Thomas K1XT firstname.lastname@example.org
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