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Re: [TowerTalk] OT: Exterior Ethernet Cable

To: Jim Brown <>
Subject: Re: [TowerTalk] OT: Exterior Ethernet Cable
From: "Roger (K8RI)" <>
Date: Mon, 11 Aug 2008 18:34:19 -0400
List-post: <">>
Jim Brown wrote:
> On Mon, 11 Aug 2008 14:19:21 -0400, Roger (K8RI) wrote:
>> I have one run that is 133' and parallels the cables to the tower from 
>> the shack. It actually runs with them for about 10' as well as another 6 
>> to 8' in the ham shack where the modem, router, and switch are located. 
> Proximity to coaxial cables doesn't matter for differential mode coupling, 
> only for common mode coupling of common mode current on those other cables. 
Which was my point. Those worried about RFI shouldn't normally have a 
>> About 40' (between the garage and shop) of that run is directly under 
>> one of the 40 meter sloping dipoles. 
> That part of the run matters -- it is coupling between the ANTENNA and the 
> cable. But that is primarily COMMON MODE coupling. A common mode choke 
> fixes that problem. 
Doesn't seem to be a problem even though the common mode can be measured 
in volts.
The equipment is all well grounded and the computers use full size steel 
cases. I'd bet two guys my size could stand on most any of them.
>> It also runs within 10' of the tower base. 
> Doesn't matter, except to the extent that it gets close to a beam on that 
> tower! Again, common mode is the potential problem. 
It do when lightning is taken into consideration, but I've never had a 
problem.  The tower has been hit at least 5 times since the network went 
in. Several of those times was during large file transfers over that 
run.  The lights went out, the UPSs squealed, something made a sound 
like a dying squeal that just tapered off, but the interruption wasn't 
long enough to even lose the connection and the files transfered without 
>> In the shop the computers are setting within 2 to 3' of 
>> the rigs, which run the legal limit.  
> Doesn't matter. Virtually all rigs are shielded, and SHIELDED EQUIPMENT 
So does feed line with high SWR.<:-))  But again I was pointing out that 
being close to RF normally has little effect.
> 73,
> Jim K9YC
Roger (K8RI - ARRL Life Member)
N833R (World's oldest Debonair)


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