RE: Topband: TOP HAT GUY WIRES

["Donald Chester" <k4kyv@hotmail.com>]

... did you
> take any special precautions in attaching to the mast/tower for good
> electrical conductivity?
>
> I installed lengths of tinned braid under the guy wire clamps, and attached
> these to the tower with burndy connectors, but have discovered some 
> evidence
> that the braid/guy wire connections have begun to break down after just a
> couple of years.  I'm not sure if it is arcing (seems impossible with the
> mechanical nature of the connection) or galvanic, but the connections are
> not like they were when installed even though protected from the elements.
>
> I cannot use copper wire for these tophat/guy wires as the load would be 
> too
> great in the wind/ice conditions we sometimes encounter at this QTH.
> "Aircraft cable" was the only choice possible.

Make sure you do not have any galvanised metal in contact with copper.  I 
suspect your tinned braid is made of copper covered with a thin layer of tin 
or nickle plating, and your guy wires are galvanised steel.  When zinc 
contacts copper, and water is present, you have a miniature battery and the  
connection immediately begins to deteriorate due to galvanic action of the 
metals.

I found that out the hard way years ago when I made an open wire feedline 
out of copper wire, but used galvanised steel wire to secure the feed lines 
to the spreader insulators.  It worked very well for a few days, but after 
the first rain, I had terrible TVI.  Upon inspection, the galvanised wire 
that was wrapped around the copper was heavily corroded.  The tie-wires at 
each insulator reacted with the copper and each junction became a diode 
rectifier.  I took down the feedline and replaced the galvanised wire, which 
I happened to have on hand when I built the antenna, with copperweld of 
similar gauge, and never had any recurrence of the problem.

My present tower is hot-dip galvanised, and I have open wire line spaced 
inside the tower up to the antenna.  I found that rainwater dripping down 
the copper feedline contained enough copper to react with the zinc 
galvanising on the bottom of the tower and turn it green, so I had to 
fabricate a couple of drainage tubes out of automotive water hose to direct 
the drip away from any metal on the tower.

If you attach copper tophat to a galvanised mast, use brass connectors.  
Brass won't  react with either metal and makes a good intermediate agent 
between the two metals.  Ground clamps are made of brass specifically for 
that reason.

Don K4KYV

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