FW: [TowerTalk] Re: getting coax into shack thru wall

[Tom Rauch]

> Date:          Fri, 29 May 1998 08:42:00 -0600
> From:          Dave D'Epagnier <DAVED@ctilidar.com>

> > My next closest tower is 250 feet from the house, and 200 feet tall. 
> > It is grounded by many thousands of feet of radials covering a ten 
> > acre pasture. That radial field cuts off before reaching the power 
> > line ground and house.

 > 
 > Tom, with this senerio aren't you providing a low impedance path
 > to house ground through your antenna coax shields? The idea of
 > providing a low impedance alternate path to ground via copper
 > strap is to let the current flow through it to your house ground
 > grid (outside the home) instead of through your coax shield and
 > into your home. 

No, read what I wrote below again. If it isn't clear, I'll try to 
explain it better.

I wrote:
> > At my "last line of defense" at the edge of the pasture, I have 
> > lightning retarding chokes both before and after a separate 
> > driven rod independent ground. When I know of a storm, or when I go 
> > away, I pull the plugs on ALL the cables at that point and pull 
> > them back several feet.  

 > How do you isolate your coax shield from house ground then?

As explained in my paragraph above. Series impedance from common 
mode chokes PLUS total disconnection.


I also wrote:
> > That's true IN the house, or ON the tower, but you certainly don't 
> > need to make the house ground follow the tower ground if you can 
> > avoid it. If the tower is right against the house, the best idea is 
> > to bring grounds and cables all up together with minimal potential 
> > difference. If the tower is remote from the house, keep the grounds 
> > isolated but STILL use the common point method at each end of the 
> > system.
> > 
> > If the distance is greater, the problem becomes one of  isolated 
>> systems. Keep them that way if possible.

Let me expand on that. At my TV set and stereo I connect ALL the 
devices to a common outlet strip. That strip has MOV's and bypass 
caps with separate series chokes in each lead. The coaxial cable 
containing TV/ FM signals and speaker leads all are bypassed and 
connected to this common point, before continuing up to the 
equipment.

I have absolutely no RFI, and few worries about lightning going 
through the equipment even though I never pounded a ground rod 
through the floor! The TV set and stuff sitting on it are all one 
independent system that floats together.

That TV set, as well as all my others and my ham shack, are treated 
as isolated systems with a common "connection entrance" point at 
each system. Little or no differential current can flow past that 
common point, and differential voltages inside the coax and power 
wires are bypassed with MOV's or other methods.

The house is treated as another isolated system, with a common point 
ground at the entrance.

The TV antenna, power line, antenna, and telco leads coming into the 
house are all grounded at the entrance point to a long buried 3/4" 
copper tubing running along the house, with 3 ground rods and 5 or 6 
straight bare # 10 buried radials silver soldered to the tubing. 

Not only does this method help prevent lightning damage, it cures 
RFI. I used this method in an apartment building that was located 
OVER the radial system of a high power AM broadcast station. It cured 
RFI that other methods failed...correcting most apartments WITHOUT 
use of a high pass filter! The building entrance was one common 
point, the breaker box another, and each TV set another.

73, Tom W8JI
w8ji.tom@MCIONE.com

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