Re: [TowerTalk] Grounds, 'remote' towers, 'house' power system

["StellarCAT" <rxdesign@ssvecnet.com>]

Please forgive me - I'm not saying its bad practice or one shouldn't do it - 
just trying to understand why.
Lets differentiate between what is always said "you need to connect the two 
together" and WHY you need to do it. Again - if there is a long distance 
except as a DC ground most any kind of connection is going to be a poor if 
not non-connection at RF! So why do it? There will be minimal current 
through it - especially if you've done your job at the tower where there is 
a much lower impedance path to ground. Its not going to take the higher 
impedance path (or of course it will but in proportion to the impedances 
seen) just because its there.
I don't see a reason why other than DC ground.

Now there is a case if it serves as a radial from the tower - but even 
then - even if a good path most of the energy will be dissipated at the 
tower.
If you have a single point ground at the service entrance (which again isn't 
the greatest from a lightning standpoint unless you're connecting at the 
poles ground - which my pole has a #4 wire at best from the top to the 
ground) .... and you bring the shack ground connections - lets assume 
they're all 0 impedance in the shack for discussion sake - if you bring that 
to this same point then if there are no currents through the control 
cables/coax then the shack will "float" with the service ground - and there 
will be no voltage differentials nor currents IN the shack... but 0 
impedance through the coax/cables?
So.... seeing a clearer picture here... lightning strikes the tower - the 
voltage at the base of the tower and the ground in immediate contact will go 
up and reduce as a factor of distance from the base... so if the cables are 
elevated to that voltage now there is a voltage differential between that 
end and the shack... current flows... if at the shack the voltage 
established reference to the DC ground is higher than at the service 
entrance (through the earth between it and the tower base - assuming no 
connection) ... then indeed you're going to have the likelihood of a 
problem.
Adding a connection will act 'better' than the earth in reducing that 
voltage differential between the service entrance and the tower base... but 
its all relative! How much more is the question - especially when, once 
again, its hundreds of feet away.

Gary

_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk