[TowerTalk] Commercial towers and lightning

[Ethan]

Bill Turner wrote:
> The comment was made a few days ago about how commercial and emergency
> radios must continue to operate despite direct lightning hits and that
> got me to wondering about something. I know there are experts here who
> would know the answer.
>
> In the case of us hams, the antenna is almost always placed at the
> very top of the tower. Do commercial and emergency installations do it
> the same way? I'm thinking that a non-rotating antenna would be better
> protected against lightning by placing it several feet lower on the
> tower and letting the top most part of the tower protect it. 
>
> Is that the case?
>
> 73, Bill W6WRT
>   
Commercial towers use lightning rods quite often, though not always.  
There are almost always antennas at the top of the tower, simply because 
that's the only position that's not partly shielded by the tower 
structure.  Typically the antennas used are DC grounded, much like a 
J-pole antenna.  The coax shield is also bonded to the tower near the 
antenna and at the bottom of the tower, at the entrance to the building 
as well.  The building has grounding strips all around it, and lots of 
ground rods on the tower and around the building.  The best surge 
protectors and lightning arrestors money can buy are hooked up, and a 
spare radio is ready to hook up in case a direct hit should take out 
your radio in spite of all the precautions.  Even radio and television 
broadcasters will typically have a backup transmitter for such 
occasions, and I've even seen television stations with two complete 
antenna systems on separate towers a few feet away from each other!  And 
yes, commercial and emergency radios do get taken out by lightning all 
the time.  It's just a risk you take when you put your antenna up so high.

Ethan (kc8hes)