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[TowerTalk] TH-7 Rebuild Experiences

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Subject: [TowerTalk] TH-7 Rebuild Experiences
From: (bill thomas)
Date: Tue, 06 Mar 2001 09:09:04 -0600
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
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