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[TowerTalk] Cleaning/referb of antennas

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Subject: [TowerTalk] Cleaning/referb of antennas
From: (
Date: Sun, 23 Sep 2001 15:43:00 EDT
In a message dated 9/18/01 9:57:59 AM Pacific Daylight Time, writes:<< 
 Hi all,
  I'm in the process of cleaning up/refurbishing a tribander for the winter
 season. I cleaned out all the traps, used new h/w where needed etc.
 Put the thing back together and in the air. It worked great for about a
 week till we had some rain.... SWR on all bands shot up to over 3:1.
********** This goes unnoticed by those who don't have a full time SWR bridge 
in the circuit. A pattern change can occur like reduced F/B without a 
noticeable SWR change.  This doesn't happen with quads and a properly solder 
joint (1 per element)
 Took the ant. back down and went thru it again. I noticed the "old" 
 Noalox in the tubing joints was somewhat caked on contained alot of
****So have others!
 When I took the ant down, I put the 259B on it and found the resonant
 freq on all bands about >800kc high on all bands, which is about 100kc
 higher than when up in place and the SWR went crazy.
********That's a fair change.  Perhaps a clamp wasn't tight enough.
 I started cleaning the gray gunk from the joints with great difficulty.  
*********A high power W6 I know had to use a file to get Penatrox off.  He 
"RF cooked the Penatrox." I've had Penatrox joints go bad also 6 blocks from 
salt water back in 1958.  Perhaps the zinc conductive particles in it change 
if the Penatrox grease doesn't keep the moisture off them.

Didn't really know what to use to clean up the joints and went rummaging
 around the garage... I ended up using Ether (AKA engine starting fluid).
 This stuff on a paper towel, easily cleaned up all the tubing joints like
**********I have a series of steel brushes and also brass shot gun barrel 
brushes I mounted on the end of a 12" rod rotated by a drill motor.  The 
places that sell nuts&bolts sometimes have these steel brushes.

 Used the paper towel wrapped around a round dowel to clean the inside of 
 the larger tubing. The tubing came out really clean/shiney and with no
 I did a dry-fit of the driven element with proper dimensions and the 259B
 said the Resonant freq was right on where I wanted it. The res. freq
 should drop a bit when the antenna is in the air.
 Now that I've put you all to sleep, here are a couple of questions:
 1. Why did the moisture mix with the Noalox? 
********There was nothing to stop it. 

2. Did the moisture cause an "insulating" barrier causing the SWR
********Do you have better explanation?  You had a "capacitive joint."

 3. What does everyone use to clean out the tubing joints? (Any cleaning
      solution in a pinch?)
 4. What are the disadvantages of "dry-fitting" tubing joints and using
 the antenna as is? I have no problem taking the antenna down every couple of
 years for maint.
*******Sounds like a good plan for yagis.  It creates a "Saw Tooth 
Performance & Efficiency Curve" where a quads is a straight line and higher.
 Any constructive guidance would be appreciated
 ************Use the flee Market Aluminum solder on the joints.  I rotate the 
elements in the lathe after a thorough cleaning, rotate it slowly, heat with 
a BurnsOMatic torch and at the right time apply the solder.  If you do it 
right it flows perfectly.  Tubing bigger than 3/4" may need 2 torches.  No 
pattern SWR change for 9 years and it still Kicks Butt.  I'd suggest 
completely cleaning the all the joints before a contest.  If rivets were used 
to join elements you have to drill them out and re-rivet.
     I've had some good luck with just plain Silicone grease.  It keeps the 
air and moisture off the surface (the other geases seem to fail here) which 
are the 2 main elements of corrosion along with dissimilar metals (even 
aluminum to aluminum.  The joints always come apart easily.  It stops 
aluminum oxide forming with SS clamps and bolts for years even with some salt 
water spray.  Has anyone else got any data on the reliability of Silicone 

As far as conductive grease is concerned the only place where conductivity is 
needed is at the joint thin rim of diameter change.  RF travels on the 
outside and makes the jump at the joint.  Conductivity inside the joint is of 
little value ecept for DC currents--perhaps static electricity.

Ease of disassembly years later and no Aluminum Oxide is the main goal if you 
grease the joints.  Silicone grease is inexpensive, never gets hard, never 
washes off and is hard to beat with a tight clamp.  I'd grease the SS clamp 
screw and surface also.  The RF has to jump from the tubing to the clamp and 
back to the aluminum again--for each clamp joint after joint after joint.  
Would you believe it creates "Jumpy RF?"  I have a picture of the "corrosion 
pattern" of the SS clamp slots on the tubing and it went deep after being 
together for years.  K7GCO

 73 es DX
 John K1RC

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