[TowerTalk] Lightning Protection Question

[Gene Smar]

TT:

     I re-read this and my earlier post.  It may not be clear that the 
Polyphasers to which I am referring are on the ANTENNA side of the remote 
switch, not on the shack side.  Hope this clarifies what I have at the base 
of the tower.


73 de
Gene Smar  AD3F


----- Original Message ----- 
From: "Gene Smar" <ersmar at verizon.net>
To: "Jim Brown" <jim at audiosystemsgroup.com>; <towertalk at contesting.com>
Sent: Saturday, September 11, 2010 8:36 PM
Subject: Re: [TowerTalk] Lightning Protection Question


> Jim:
>
>     You overlooked my caveat in my original e-mail:  I have a remote 
> switch
> in the NEMA box at the base of my tower.  Had I installed the Polyphasers 
> at
> the shack end, only one coax run (between the shack and switch) would have
> been protected; the switch and antennaa coax runs into it would have been
> vulnerable to lightning damage.  I installed the Polyphasers in the box on
> the tower so as to provide protection for the switch and all three coax
> lines going into the switch.
>
>     As for the need for a final Poly outside my shack, I concluded that I
> didn't need one there for a few reasons.  The run is short (<50 feet); it 
> is
> underground; based on these these two facts it would be nearly impossible
> for a lightning strike to induce appreciable energy on the center 
> conductor
> of that 50 feet of coax such that I would need another Poly outside my
> shack.  (We all agree that lightning supressors are intended to shunt the
> center conductor to ground during a lightning strike, right?)  Any induced
> charge on the shield of my underground coax would be grounded at the NEMA
> box and at my SPG outside the shack.
>
>     As I previously wrote, if I had run the coax directly into the shack 
> to
> connect to the switch there, I would have installed Polyphasers outside 
> the
> shack on the SPG and not inside the NEMA box.  If Larry KN8N has a switch 
> on
> the tower, he ought to put the Poly's there.  Otherwise, I agree - outside
> the shack on the SPG.
>
> 73 de
> Gene Smar  AD3F
>
>
> ----- Original Message ----- 
> From: "Jim Brown" <jim at audiosystemsgroup.com>
> To: <towertalk at contesting.com>
> Sent: Saturday, September 11, 2010 11:53 AM
> Subject: Re: [TowerTalk] Lightning Protection Question
>
>
>> On Sat, 11 Sep 2010 10:57:06 -0400, Gene Smar wrote:
>>
>>>It depends.  I have my Polyphasers at the NEMA box at the tower base,
>>>but I also have a remote coax switch there, too.
>>
>> I disagree (and agree with K1TTT) -- lightning protection devices are
>> protecting you radios by short the voltage on the center conductor to
>> the shield. They cannot do that at the tower -- voltage can be induced
>> on the coax between the tower and the shack, and a protector at the
>> tower is too far away to offer much protection at RF. The best place for
>> them is at the entry  panel to the shack.
>>
>> The SHIELDS of coax SHOULD be bonded at top and bottom of the tower.
>>
>> 73, Jim K9YC
>>
>>
>>
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>>
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