[Towertalk] Lightning Protection

[Tom Rauch]

> >shields grounded just before they hit the suppressors out at the
> >tower. (I'd rather keep the lightning in my back yard away from the
> >house than conduct it closer to the shack before it's shunted by the
> >suppressors.)
> 
> and wondered:
> 
> Let's say I DO put my Polyphasers at the tower bases.  My coax runs
> are between 87 and 200 feet from there to the shack, above ground. 
> Isn't there a chance lightning energy can still get on the coax after
> the Polyphasers?

Yes, there is an excellent chance! First of all, remember that the 
the polyphaser, like any other discharge device or gap, must have 
significant center-to-shield voltage to fire. It also does absolutely 
nothing for common mode currents (which by far are the most damaging) 
that a good grounded feedthrough won't do.       

Second, all it takes is a high resistance shield connection anyplace 
after that point and you might as well never have had the polyphaser 
in line. The polyphaser should be the last resort last line of 
defense, NOT the first line.

A double-make double-break (form X contact) relay that opens the 
feeder and grounds it is actually **much** more effective than a 
polyphaser. 

 Is that why Gene went on to do the following:
> 
> >I also have the shields grounded at a SPG plate
> >in a steel box just outside the shack window.
> ?

SPG
Single point ground.

Gene must also have his power lines routed through there (with MOV's 
to clamps all the leads to ground and the electrical safety wire 
grounded), telco lines (also bypassed there), and everything else or 
it is NOT an SPG.
 
> What about alternatives when you have something like 16 or more
> incoming feedlines?

I have a large copper plate, and everything grounds there on 
feedthroughs. My power and telco ground there, as does the station 
ground.

Like I said, I never disconnect anything...ever. While that is not 
the best idea, it works for me because:

1.) All cables are grounded at multiple points from the antennas to 
the house.

2.) All cables are long, so the lightning has a chance to find other 
paths.

3.) All cables are buried.

4.) All cables are shielded and shields are grounded.

5.) I have a real SPG (single point ground) for all power, telephone, 
feedlines, and control lines.

6.) I have multiple RCS-8V's in my system (except VHF antennas) 
...and when power is off the feedline center conductors are open.

By the way, all of my receiving antennas and control lines remain 
connected at all times. I also have access to feedlines and control 
cables in two buildings, the house and my workshop. Each has a SPG at 
the entrance.73, Tom W8JI
W8JI@contesting.com