[RFI] Power Line RFI -- Slack Spans

[Pete Smith]

I picked up the following from a power company engineer who has been
working on my RFI problems.  Any old power line workers out there, forgive
me if I do not get the terminology 100 percent, but I think the idea is
worth passing on.

One of the worst offenders in RFI generation is what are called "slack
spans."  These occur when one or more primary wires need to cross a road or
change directions sharply but it is not convenient to guy the poles to
permit a taut wire between poles.  The wires hang between poles with
considerable slack, hence the name.  At least in our area, they used to use
the same insulator set-up for these as for a taut span (cup-shaped
insulators mounted on an eye-bolt screwed into the pole).  Because the wire
is not taut, these insulators provide an excellent opportunity for sparking
between the bolt and the metal insulator mounting fixture when they are
moved by the wind.  Many of these are still in service.  The fix is to
replace the insulators with a new type that has a rigid metal mount bolted
to the pole, such that there is no longer a loose metal-to-metal joint to
work in the wind.

Once I found out about this I was able to identify a number of these slack
spans in my area that were noisy, and the power company has been very
helpful in replacing the insulators.

73, Pete N4ZR

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