On 2012-11-15, at 3:42 PM, Bruce wrote:
> Dry blowing snow or high wind can cause quite some voltage build up on a
> antenna, especially a long one. It is possible to draw quite an arc to
> ground.
> There have been reports of high voltage electrocutions from antenna static
> build up in Short Wave Broadcast stations. A short stick was mandatory for
> maintenance periods.
> And yes, I did work at a shortwave station with 500 KW transmitter output.
>
> So receiving antenna wire insulation could have some benefit if the voltage
> on a bare wire is leaking to a tree limb or across an insulator. Beyond some
> point all insulators can fail.
>
> Indoor antennas do hear static, but I have never seen any evidence of voltage
> build up. ( The building may provide adequate insulation.)
>
>
> Out of curiosity, has anyone ever really done testing of voltage buildup on a
> insulated antenna wire, VS a non-insulated wire ?
> Indoor antennas VS outdoor antennas of equal size?
>
Hi Bruce,
I am not so sure that the notion of insulated vs. uninsulated wire holds true
in long wire spans...
Case in point: years ago when I first erected my 1500' long Beverage antenna
here, I was specific in using insulated wire though its entire course because
it runs through a grove of trees at one point. Well, one day, in the advance of
an approaching storm front, I decided to ground the end of the Beverage in my
shack. I could feel a "tingling" sensation as I man-handled the wire,
negotiating my way to the common ground pipe that I have running the length of
the back of my operating table...imagine my complete & utter shock as I neared
the wire to this same pipe, and managed to induce 1/8" long blue arcs from the
pipe to the wire!
Since that time---FWIW---I have always had a rugged 2.5 mh. RF choke clipped
between the wire's end where it attaches to the matching transformer, and
ground. In theory this acts as a static drain, I guess, but does not induce
signals to ground. I've heard that a multi-megohm resistor will do the same
thing at this point...
~73~ de Eddy VE3CUI - VE3XZ
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