[TowerTalk] Tower Isolation

[Roger Parsons]

My remote station is at a former AM broadcast 325' tower. The base 
insulator is bridged by a thick cable, and there are a number of coax 
cables going up the tower feeding various VHF and UHF antennas.

My 160 array is attached from the tower, but the tower itself does not
(intentionally) form part of the array, and EZNEC says that it has no 
significant influence. Despite this I am a little dubious - the tower is 
quite thick and must be close to 3/4 wave resonance on top band. A 3/4
wave vertical would send all my signal up into the clouds which I don't 
want.

So I would like to open the base insulator whilst I am operating (which 
will never be during thundery conditions). I can isolate the vhf feeders 
relatively easily with common mode chokes. (I don't think the isolation 
has to be that marvellous - a few hundred Ohms loss resistance would kill 
any tower radiation.) Whilst I could do the same across the base 
insulator, I would like the tower to be truly grounded during a lightning 
event..

So I was thinking of using a hefty relay which opens when the station is 
operational. The question is: How hefty is enough? The tower certainly 
receives direct strikes regularly. I suspect these might vapourise any 
reasonable relay contacts?

Any thoughts?

73 Roger
VE3ZI