Most of the used 1 5/8" Ive seen including the many rolls I have here had
the jacket removed at regular intervals for bonding to the tower.
I am "assuming" that doing similar to Dicks and attaching to ground rods
would be beneficial?
Carl
KM1H
----- Original Message -----
From: "K4SAV" <RadioIR@charter.net>
To: <towertalk@contesting.com>
Sent: Tuesday, August 14, 2007 1:50 AM
Subject: Re: [TowerTalk] Ground System
> Dick Green WC1M wrote:
>
>>>Coax shields won't take very much current before they melt. A large
>>>ground
>>>wire will lower the impedance between the tower and the common point
>>>ground, as well as reduce the voltage drop for these low frequency
>>>components.
>>>
>>>
>>
>>RG-8 style coax shields won't take much current before they melt, but as I
>>mentioned, I have two runs of 1-5/8" heliax running between the tower and
>>shack, connected to the tower ground system at one end and the SPG at the
>>other end. For those not familiar with this type of cable, the outer
>>conductor of each run is nearly 2" in diameter -- basically a big,
>>flexible
>>copper pipe with a lot of surface area. I don't have a spec on the
>>thickness
>>of the copper, but it's probably on the order of 1/64". The resistance per
>>foot is .14 ohm/1000 feet. I don't know the current handling capacity, but
>>the power rating is 310 KW. Although the heliax is jacketed, and therefore
>>won't conduct a surge to ground like a bare wire in the trench, it seems
>>to
>>me that the two large copper tubes present a much more inviting path to
>>the
>>SPG than the bare wire. True or false?
>>
>>73, Dick WC1M
>>
>>
>>
> True, and you are not going to melt this.
>
> And your numbers look close. If it is 1/64 thick, then each of these
> lines would have just slightly less copper than a #00 wire, and lower
> skin resistance. DC resistance of a #00 wire is 0.078 ohms per 1000
> ft. If it's soft copper, to get a resistance of 0.14 ohms/1000 ft you
> would need a thickness of about 0.01 inches. That's close to a #1 wire.
>
> At 10 KHz, the impedance will be dominated by inductance. The impedance
> of a solid wire with the same amount of copper as your heliax should be
> about 43 ohms/ 1000 ft, and the impedance of your heliax should be about
> 36 ohms / 1000 ft.
>
> If you have two of these routed next to each other the DC resistance
> will drop by a factor of 2 but the impedance at 10 KHz won't drop by
> half. It will drop only a small amount, maybe 5 ohms or less. The
> wider you separate the cables, the more the impedance will drop (up to a
> maximum of 1/2). (The old mutual inductance issue.)
>
> You do loose the ability to dump some of the charge into the surrounding
> ground on the way back to the common point ground by having an insulated
> wire.
>
> Jerry, K4SAV
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>
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