[TowerTalk] More about GOOing your joints

[Kurt Andress]

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From: "Kurt Andress" <NI6W@yagistress.minden.nv.us>
To: "towertalk" <towertalk@contesting.com>
Subject: More on GOOing your antenna joints!
Date: Sat, 25 Apr 1998 10:21:07 -0700
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I've finally found a bit of time to get on here and found something to =
say.
I've been watching the recent discussion on what should be put into =
antenna
connections to prevent corrosion.
When trying to figure out how to solve a problem, it is often helpful to
step back and think about the basics.=20

Basic #1 - Materials corrode or oxidize in order of their location on =
the
Galvanic Table (or chart). The Galvanic Table lists materials in order =
of=20
their relative activity in a galvanic cell (or battery).
=09
It looks something like this:=09

Platinum			Inactive (least likely to corrode)
Gold
Graphite
Titanium
Silver
Stainless Steel (passive)
Stainless Steel (active)
.......
Copper
.......
Aluminum
.......
Steel				Active (most likely to corrode)

(This table made from memory which may not be perfect)

Basic #2 - If we put two dissimilar materials together, and don't want =
them
to create an active Galvanic cell (battery), which creates rapid =
corrosion,

we need to select materials that are close together on the Galvanic =
Table,=20
not FAR APART!=20

Basic #3 - A Galvanic cell requires 2 basic elements to become active.=20
1) Dissimilar materials (materials that are not equal on the table, none
are equal, just closer than others)
2) An electrolyte (Like salt water or chemically doped fresh water, like
most rain on this planet)
Any dissimilarity between materials will create a Galvanic Cell, when
accompanied by an electrolytic solution!

Discussion:
If we are going to adequately seal an antenna connection, to keep the
electrolyte out of the battery, we can put "ANY CONDUCTIVE STUFF" in the
joint
I haven't heard of many, if any Amateurs that seal their antenna joints, =
to
keep the electrolyte out, except ON4UN who describes how to do it=20
(in Low-Band-Dxing) with shrink tubing that has an adhesive on the =
inside=20
of the tubing that bonds it to the OD of the tube sections when heated =
for
shrinking.
Adequate element sealing requires that the innermost section (near the
boom)
is completely sealed off to prevent water from running down the inside =
of=20
the elements and getting into the joints. =20
If you seal your antenna connections, feel free to squirt some graphite
dust into a cup full of WD40. Your battery will not work very well =
without=20
the electrolyte!=20
Graphite is extremely conductive, but look how far away it is from=20
aluminum on the table!

If you are not going to seal your antenna connections, you are in good
company with 99.99% of the rest of the world.
I just wonder why so much attention has been paid to sealing the handful =
of
connections in the feedline that leads to the antenna, but none to =
sealing
the multitude of connections in the antenna? Joint compounds do not seal =

the antenna joints! They just put some "STUFF" in there to slow down the =

migration of water into the joint, and the subsequent corrosion.=20
When the compound liquid leaves, moisture takes its place.

Galvanic Cell basics tell us that we don't want to put anything in our
antenna joints but aluminum based compounds.=20
We can't "Just put some STUFF in there" to "get a good contact"=20
(sounds like a list operation!).=20
Our experience tells us that the liquid stuff in the joint compound =
leaves=20
after a few years.That's why the joints appear dry when we take them =
apart.

We don't visually see the moisture in the joint, but it's there!=20

The reason why unsealed joints, with aluminum based joint compounds, =
work
for many years is entirely due to the partial sealing effect of the =
joint=20
clamping mechanism. It traps thousands of the joint compound particles =
in=20
intimate contact with the tubes.
These connection sites are pressed together with significant pressure =
and
it takes a while for the water (electrolyte) to get to them.
That is why I favor Stainless hose clamps over other types of single
pressure point screw lock devices. The hose clamp presses a larger area =
of=20
particles and tubing together!

The Bottom Line:
If you plan on keeping the moisture out of your antenna connections, put
any concoction with conductive particles in the joint!
If you don't want to seal the connections, put only aluminum based
compounds in the antenna joints.
Here's how to tell the difference:
Graphite is black in color. If your compound is black it probably has
graphite in it.	Completely seal the antenna connections.
If your compound is copper colored, completely seal the antenna
connections.
Aluminum is silver or gray in color. If your compound is gray it =
probably
has aluminum in it. Don't seal joints and wait for nature to=20
take its course.
I use the gray stuff, NoAlox or other names.=20
The copper colored stuff for use in tower and station grounding system.
This is what PolyPhaser supplies for their lightning grounding
systems. Went to their classes last year, pretty neat stuff!

73, Kurt

YagiStress - The Yagi structural modeling software for Antenna =
Designers!
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