[TowerTalk] Conduit for cables to the tower?

[Jim Brown]

On Wed, 13 Sep 2006 21:35:52 -0400, Alan NV8A wrote:

>I have questions about the best way to get cables (coax, AC, and 
>control) from the shack to the tower.

Several comments. 

First, use TWISTED PAIR for all control cables and for power. This 
minimizes crosstalk/noise to control lines. Don't bother with 
shielded cable -- cable shields provide NO magnetic shielding, and 
virtually all coupling below 1 MHz or so is magnetically coupled. 
Twisted pairs also reduces the coupling at RF. 

Second, I wouldn't be so quick to dismiss the importance of steel 
from a lightning protection point of view. A lightning hit will 
cause a lot of current to flow in the earth, far from a perfect 
conductor, and significant potential differences will be created. 
Polyphaser is in that biz, and has certainly studied it more 
carefully than most of us. 

Third, I fully agree that the price of the conduit itself is a 
small fraction of the total cost of the conduit system, so if 
steel is safer (as Polyphaser says), that's the way to go. Yes, it 
must be 

Fourth, I read the code the same way that Jim Lux and Phil Camera 
do with respect to the separation of power and low voltage wiring. 

Fifth, I see NO problem running control lines with the coax. 

And finally, the code rules about the number of bends ARE related 
to ease of pulling and damage as a result of pulling. And it's the 
number of bends between accessible pulling points that is what 
matters. 

Jim Brown K9YC