Topband: Tower-attached guy wires - max length for driven tower?

[Donald Chester]

Brian K1LI wrote:


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Use strain insulators next to where the guy wires attach to the tower.  If you run over a few hundred watts peak power, series two or three insulators in a chain right at the attachment points.  Then break up the guys with strain insulators at intervals along the length of each wire.

For AM broadcast towers the NAB engineers handbook recommends a maximum of 1/7 wavelength for sections of cable between insulators. This calculates to 74 feet for 160m, or 37 feet for 80m.  

To make my tower guy wires rf transparent through 40m, I installed insulators every 18 feet.  But that would be overkill unless you planned to use the tower as a vertical radiator for 40m; my tower is 127' tall, so this required over 100 insulators. At 37 ft. intervals, yours should require roughly 30-40 insulators.  

I used 6 cable clamps at each insulator.  The clamps were cheap at the time, and I used surplus "johnny ball" insulators.  If I  had it to do over again, I would use pre-formed guy grips, two per insulator.  The only cable clamps I have seen available to-day are merely zinc coated and cost several times what I paid for mine, which are true hot dipped galvanised. The guy grips are a little more expensive, but are much easier to install and are supposed to be more reliable than the clamps.  I used grips when I had to replace some insulators that were damaged from a direct lightning hit.

Don k4kyv








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