Loop In Coax Help Prevent Lightning Induced Surges ?
W_Tom wrote:
"Do you think the loop will stop what three miles of sky could not?"
Depends on what kind of loops and how many.
I`ve worked in several broadcast stations that often got struck by
lightning. Their towers were the tallest things around. None of these
stations got significant damage from lightning. In addition, none of the
station equipment powered from the mains or appliances plugged into the
mains at the station ever was damaged.
All these stations used tower lighting chokes, one coil for each tower
lighting wire including the neutral going up the tower. Three wires,
beacon, side lights, and neutral were usually accommodated with tower
lighting chokes. Their primary function is to avoid sapping any of the
r-f energy from the tower. Another benefit is that the chokes reject
lightning too. They are substantial and all turns are wound side by side
(trifiler?) around a large ceramic coil form. The wire is large enough
to easily handle the load current. I never worked at a station that used
Austin tower lighting transformers instead of chokes, but I`ve seen
enough of them to suppose they must isolate about as well as chokes do.
One station I worked in had an FM antenna atop one if its AM broadcast
towers. Its FM coax was coiled at ground level to isolate the AM r-f and
it rejected lightning too. So, if you have enough of the right turns the
choke does effectively reject lightning. Inductance is proportional to
the size of the coil.
Best regards, Richard Harrison, KB5WZI
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