Tom,
In the past, I remember you mentioning the use of common mode
chokes (air wound) for lightning protection. Do you put these
on the shack side of your SPG bulkhead or do you put them on the
antenna side of the SPG with another set of ground connections on
the antenna side of the chokes?
Thanks,
Mike, W4EF...........
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: <towertalk@contesting.com>; "Mark Beckwith" <swca@swbell.net>
Sent: Wednesday, May 15, 2002 7:32 PM
Subject: Re: [Towertalk] Lightning Protection
> > >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
>
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