I believe it was the Polyphaser book that suggested that ground rods should
be spaced no more than twice the length of the ground rod. So, for common 8
foot ground rods the spacing should be not more than 16 feet apart. There
was a rationale to the spacing but it escapes me at the moment - charge
distribution during a strike most likely.
73, Larry W6NWS
----- Original Message -----
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
To: "Drax Felton" <draxfelton@gmail.com>
Cc: <towertalk@contesting.com>
Sent: Tuesday, October 07, 2008 12:29 AM
Subject: Re: [TowerTalk] Grounding with Polyphaser lightning arrestors
> Drax Felton wrote:
>> My 70 ft. tower is going to be 5 feet from the corner my house with
>> several
>> runs of coax from the tower base to the radio room.
>> Those runs will each be about 25 feet long to the radio.
>> To start out I'm going to have three ground rods about 15 feet apart from
>>
> Typically the ground rods should be much closer to the base of the
> tower. Say about a foot or two outside the concrete. Grounding cables
> make gentle curves from the tower legs to the rods. The around 16' out
> you put another ground rod on each run (IOW about twice the length of a
> ground rod)
>> each other in an arc around the tower and connected to each tower leg and
>> then one another.
>> Then one of the tower legs will be connected to the electical service
>> ground
>> which is also maybe 8 feet away,
>>
>>
> I'd tie the grounds together through the ground cables.
>> Should I install my Polyphaser lightning arrestors at the bottom of the
>> tower or at the entry point where the coax enters the house?
>>
>>
> Typically you ground the shield of each coax to the base of the tower.
> The Polyphasers go on a grounded bulkhead where the cables enter the
> house. This also grounds the shields at that point. I have one ground
> run from the tower along the conduit to the entrance bulkhead There are
> ground rods, CadWelded(TM) to the cable every 16 feet (give or take a
> bit) and one right at the bulkhead. If you go to W8IJ's page you will
> see he doesn't use anything other than a good grounding system.
>> I was thinking about putting the arrestors on the tower base. I would
>> then
>> put ferrite beads over the coax and make a choke out of the coax where it
>> enters the house on the premise that this choke point would look high
>> impedance to lighting. Am I off-base in my thinking? If its an alright
>> idea then how many turns of what diameter of 9913 coax makes an effective
>> lightning and common mode choke at HF and at 6 and 2 meters?
>>
>>
> I think you will find that these types of chokes are relatively
> ineffective against lightning.
>
> 73 and good luck,
>
> Roger (K8RI)
>> -Drax
>> KB3X
>> _______________________________________________
>>
>>
>>
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>>
>
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