[Antennas] DC ground a collinear?

[Eric Lemmon]

Mike,

A lightning strike has an extremely fast rise-time, so it appears to be a few
cycles of a high frequency RF signal.  Commercial vertical collinear antennas-
such as those made by Celwave RFS and Decibel Products- are solidly DC grounded
and are therefore shunt-fed at the appropriate tap for the operating
frequency.  Such an antenna must be solidily clamped to a steel tower that is
solidly grounded, or grounded by a LARGE copper conductor (4/0 or larger) that
is solidly connected to the antenna mount and which goes straight down to an
array of ground rods.  I use the word "solidly" to emphasize that flimsy
grounding wires that might be suitable for grounding a hair dryer are woefully
incapable of carrying 100,000 amperes caused by a lightning strike.

My philosophy on grounding antennas was validated when my UHF repeater antenna
on a nearby hilltop was struck by lightning, but the repeater never went off
the air.  I did not learn of the strike until I saw that the grounding wire had
ripped free of its clamps- caused by the magnetic forces created by a huge
stroke current.  I guess the best advice I can offer is to be a pessimist when
it comes to lightning protection grounding:  My antenna WILL be struck by a
destructive bolt of lightning, and I WILL design a grounding system to handle
it!

73, Eric Lemmon WB6FLY

Mike Gilchrist wrote:

> How do the commercial guys DC ground a vertical collinear?