I've always wondered about terminating coax shields on the top of a crank-up
tower. On one hand, I think that by doing that, you're encouraging lightning
currents to go down the coax shield as the resistance between the tower
sections of a crank-up is likely to be larger than the coax shield (assuming
the shield is also bonded at the bottom of the tower). But perhaps the
inductance of the coax is larger than that of the tower so most of the
lightning current would still traverse the tower? On the other hand, by bonding
the coax at the bottom and not at the top, you may have flash-over issues at
the top because of the difference in potential of the tower and the coax shield
at the top. Maybe I'm making this more complex than it is, but my gut tells me
it is a bit more complex than it may first seem.
All the commercial towers bond coax shields at the top, bottom and every 70-100
ft or so, but they are not crank-ups with unknown continuity between the
sections.
N3AE
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