[TenTec] On Grounding

[ac5e at comcast.net]

Good  info from K4TAX. 

Personally,  over the last half century plus of playing with RF I have always figured the RF should be inside the TX/tuner/coax, etc., and any and all attempts at an RF ground should be done between the TX and the antenna. And the closer to the antenna the better.  If the RF isn't confined - thinking about one 20 KW RF heater/sealer  I dealt with many years ago -  the operator is likely to have problems.  But the solution to that problem is to stop the leak, not shunt RF to ground. 

Of course, twinlead of any and all sorts is a different matter but unbalance in an open wire fed system should not occur, and any that does occur should be taken care of automatically in the line to antenna matching network.  

Now, the NEC requres a power ground under the "meter base," "meter loop," or whatever sort of box the electric service connects to. In my experience that ground connection is a hangover from the times when most houses had cotton covered wiring and a few bare bulbs hanging from the ceiling. It's usually adequate for about three amps and pitiful when the load becomes more unbalanced than that. Or when those big sparks are trying to go to ground and that high resistance ground leaves them looking for a better path through everything in the house. 

Since I have looked into the corpses of a few thousand lightning hit and unrepairable devices I prefer something with a little more current carrying capacity.  

Here - there's three double extended ground rods going down over 20 feet, connected together with 32 feet of half inch soft copper refrigeration tubing brazed to the rods. Along with the mandatory run of #10 from the power line neutral to the center rod.  Of course, that chunk of #10 is paralled by a piece of 2/0 copper so there is a pretty low resistance electric service ground; along with a "whole house surge protector" in the box.  The system seems to be working since I have had no damage even when most of the houses in the neighborhood had severe lightning damage. 

The tower is also fairly well grounded. Taking some advice from the local two way guys I sank an 8 inch hole to below the mininum water table through the bottom of the base excavation.  Two sections of "drill stem," essentially 6" schedule 80 steel pipe, with ground lugs welded to the top provide a substantial ground rod for the tower; and substantially stiffen the tower structure as well.  "Starter cables" from the NAPA store provide a low resistance path from the tower proper to the ground in the center of the tower base.  

The coax runs through tower mounted ground blocks, and both the coax and rotor cables go through lightning arrestors mounted on the drill stem. From there they run to a grounded bulkhead at the shack.  There are reduntant arrestors on all incoming lines at the bulkhead, and a "line isolator" inboard of the bulkhead to discourage any remaining energy from coming visiting.  And yes, there is a piece of #10 from the bulkhead to the power line ground and another to a tower base bolt.   

With more than 90 "lightning days" a year I'm not surprised the tower takes a hit a couple of times a year. My neighbors are good about telling me about it, too. I think the nonogenarian lady down the hill sits in her window and stares at my tower every time it thunders! However, I have had NO damage in the shack of any sort whatever. Now the first remote antenna switch was another matter. 

Anyhoo, that's my war story on the subject.  And from observation, if you can put one in  a "Ufer" ground is far superior to any ground rod - and backing  a Ufer ground in the slab up with a halo ground around the protected building is even better. 

73  Pete Allen  AC5E


--
Never squat with your spurs on


> This is excellent. I've believed for many years that most amateur ground
> system present more of a hazard to equipment than a help. Manufacture's
> manuals all recommend a "good ground" however but this could be just a CYA
> thing. Connecting the tower and coax shield grounds to your power line
> ground isn't often easy and is seldom done. My Electrical entrance is
> grounded to one old, beatup looking piece of conduit driven outside many
> years ago and it's effectiveness is questionable. Running a large wire
> between the coax of my dipole and that ground rod would be very difficult
> and very long.
> One thing I've done over the years is to use a large knife switch to
> disconnect and ground my antennas when I've not on the air. The station
> ground is not connected to the rig at all and the antenna ground rods are
> used only to ground the antenna when I'm away. Somehow I got the idea that
> having that big wire over the house, connected to ground acts as a constant
> path for static buildup and may even help protect the house.
> Having 2 ground systems, one for the electrical and one for the rig is
> really asking for trouble and I suppose the interconnecting wire is the
> cure. I'm going to revisit this in my shack and see if it can be done.
> 
> Steve N4LQ