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Author Topic: Tower Ground/Station Ground  (Read 8876 times)
K4FMX
Member

Posts: 17




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« Reply #15 on: February 16, 2013, 02:32:11 PM »


I am a little late on this post but I just saw the comments here on grounding.

First rule is you want all grounds bonded together.
At the tower you do not want a ground rod "under the concrete". You do not want any metal coming out of the tower base below grade. This will rust and allow rust to creep into the concrete and crack it. All metal coming out of the concrete should be above grade with some slight slope away so water does not collect around it, including tower legs/J bolts.

Assuming you are using J bolts in the tower foundation, tie them to the rebar in the foundation and tie all the rebar in the foundation. Do not weld! Unless you use special rebar that is rated for welding.
This will give a very good auxiliary lightning ground for the tower.

In addition place the 3 (minimum) ground rods around the tower. Do not bond the ground rods to a common point and then run a cable to the tower. Rather run a separate ground lead from each ground rod to each leg of the tower. The tower is the common point for the ground rods.
More ground rods can be added out away from these and bonded to the existing rods.

So far you have the ground rods and the tower concrete base (ufer ground) bonded together for the tower ground.

All cables should be bonded to the bottom of the tower and at the top. You should run a #6 bare wire over to the shack ground. The bare wire will also act as an additional ground radial connection to earth as well as a sure bond to your entrance panel.
There is really no need for polyphasers at the bottom of the tower, only at the shack entrance.

At the shack entrance you want a "single point ground". This is where all of the protection devices are mounted. Any thing that goes into or out of the shack should be directly bonded to that panel including RF cables, phone lines, TV etc. and your AC protectors. If this panel is located very close to your AC service panel that is good. An AC protector in the service panel will do the job. Be sure to directly bond the AC service panel/ground to your single point ground panel.
If your AC service panel is some distance away from your single point ground panel you can run an AC line over near this panel with outlets and protection devices in it and directly bond it to the single point ground panel. This is the cure for having the AC panel a long ways away from your single point ground panel.

Of course now you need another ground field of several ground rods that are tied directly to your single point ground panel as the tower ground system is too far away to be effective here.

All equipment ground leads can run directly to the single point ground panel but you don't need to get too carried away with these ground leads.
The whole idea of a single point ground system is to have a common bonded point for ALL leads entering the shack so that in the event of a lightning strike there is no voltage between any leads. This will prevent any voltage coming in on one line (antenna lead) going to a radio and leaving the radio on another line (power line). If all lines are clamped to the same potential you will not have the equipment (radio) in the middle of a loop.
Now all of the leads may get elevated several thousand volts above ground during a strike (depending on how good a ground system you have) but there will be no difference across the equipment to cause damage.

When installing ground rods, drive them in. do not dig a hole and back fill the hole or use water to wash them in as you loose soil compactness around the rod.

No braided cable for ground connections. It will corrode and not have as good a connection between strands. It is not even good to use inside.
Solid wire or copper strap (best) outside. Stranded wire will corrode at the connections and it is impossible to clean to renew the connection. Large strand cable is ok if cad welding.

73
Gary K4FMX


Hi all,

Thanks again for the information...  I was not going to back fill the tower hole, but the holes for the ground pipes...  I have been doing lots of homework, and here is what I intend on doing, unless someone comes up with a reason to not do this...

1.  Dig large hole for tower base.
2.  Construct the rebar and place in hole...
3.  Add a ground to the rebar, run up and out of the base to teh tower legs.
4.  5 feet out from each cornner drive in a 10 foot ground rod into a trench about three inches deep.
5.  Connect with #4 to all rods, Cadweld them all...
6.  Back-fill the grounding trench, not the tower hole...  Smiley
7.  Run this ground to a dissimilar metal connector to each tower legs, one for each leg, and two on one leg.
8.  Run this ground also to an external box, with a 1/8it inch copper sheet in it.  Polyphasor stuff on the sheet, coax yhrough the polyphasors...  This is a covered, sealed cable system box used to mount cable amps in... 
9.  All cables out of the box, via water sealed PVC to an underground run of Coax, and Rotor control...  I am getting a rotor Lightening arrester for the box as well...
10. Same set up as the cables enter the house, Box, copper sheet, Polyphasors etc...

I have already re-built the station inside...  It is described on my web page under Station Information...  Basically there is now a copper bus bar running the length of the desk, with tapped screw holes for every peice of equipment that can be grounded.  This will connect to the same ground entering the hose, which is also the House electrical ground, and which will be tied to the tower ground, via the Coax Shields...  Using 4000 MAX from DX Engineering... 

Question is do I create a ground look doing it this way?  Three ground sections, tied together with largish cables...  One 100 feet from the other two, which are about 7 feet from each other, so they essentially become only one ground... 
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