[TowerTalk] ladder line

[Paul Christensen]

> If you are doing this to protect the radios, etc. when not in use I
> would be concerned that the narrow gap between the contacts might
> easily be jumped by lightning. Tim, N9PUZ

Obviously, there are no guarantees with lightning since it travels through 
air a distance of a mile or more before ultimate damage results.  Still, the 
opening of both sides of the line may be enough to avoid some, if not most 
strikes.

My vacuum relays simply open as a knife switch without grounding.  However, 
one other possibility is to find SPDT vacuum relays (scarce), or add another
pair of vacuum relays from line to ground.  So, one pair of relays have NO 
contacts, while the other pair is NC.

I've toiled with the above idea for almost 20 years and I keep coming away 
with the thought that the open line to the antenna is better left floating 
open rather than
tied to ground when not used.  I am not sure what purpose is served by 
making the antenna and line more attractive to a lightning hit by grounding
it when not being used.

Yet another idea is to use the setup above, but only ground the rig side 
when not in use and float the line and antenna.  That arrangement seems to 
make more
sense.  Commercial coaxial switches ground unused ports generally because 
there's never a total disconnect from the coax shields.  The shields on a 
coaxial switch are always remain connected together and form a lightning 
path into the shack.

For ladder line, I think a simple break of the line with a pair of SPST 
vacuum relays is a reasonable compromise.  So far, no lightning issues here 
in Florida for 20 years.  Prior to the use of the vacuum relays, equipment 
burn-out was a continual problem when I would forget to manually disconnect 
the ladder line.  By using remoted vacuum relays, you can mount them a safe 
distance from the house and configure contact activation to follow the rig's 
on/off state.  Again, using the relays is no guarantee, but I would say in 
my experience that it's better than leaving the line connected at all times. 
My only other alternative is to disconnect the line and throw it out away 
from the house when not in use.  That's not a viable option for me.

Paul, W9AC