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Re: [TenTec] RF Ground

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] RF Ground
From: "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 7 Apr 2009 21:00:17 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
This addresses lightning protection procedures:
My experience and studies conclude when it comes to lightning protection, 
deep is not near as  important as surface area covered.  Reason being is 
that most of the lightning energy is discharged within the first 18" of 
depth with regard to the earth.  Basically this says for a 100 ft deep well, 
only about the first 1.5 ft counts.  Surface coverage is what you are 
looking for, not depth.  This is why broadcast stations use radials buried 
less than 12" deep, thus to couple to the earth and reduce earth loss. 
Also, it is not an accepted practice to put a driven ground at the end of a 
radial either.

As to putting ground rods through my basement floor, I would never do that. 
I've seen too many concrete foundations cracked due to massive heating of 
water under them during a lightning strike.  Water can go from liquid to a 
large amount of steam in less than 1/2 second and the pressure generated is 
immense.  Anything you do you want outside of the structure unless you want 
the lightning energy inside with you.  Not good!

As to station ground rods, just be sure that you have a #6 AWG copper or 
larger connected between the station grounds and the electrical ground at 
the service entrance.  This includes any driven ground at the base of the 
tower.  It needs to be bonded back to the service entrance ground.  Also be 
sure any other driven grounds for equipment is also bonded back to the 
electrical ground.  This includes cable TV block, telephone network block, 
satellite dish, TV antenna and etc.

Now for a word on RF ground:
Actually most HF antenna systems in common use today do not require a ground 
to operate efficiently. Exceptions are verticals, end fed wires and slopers 
to name a few.  In this case, more than a few driven ground rods are needed 
and thus one should consider several up to a 100 or so 1/4 wave radials as 
part of the antenna ground system.  On the other hand, a dipole be it 
balanced or unbalanced fed, center fed wire or beam does not require a 
ground.  Actually your station does not require a ground to operate 
satisfactorily as any matching network or tuner should implement efficient 
transfer of RF energy to the antenna system.  If you have RF in the shack, 
best look at your antenna and feed system.  I suggest common mode chokes at 
the point where the coax connects to the antenna for starters.

Folks, it is springtime and springtime brings thunder preceded by lightning. 
Make sure your system is ready for it.  Safely too.

Bob, K4TAX

----- Original Message ----- 
From: "Jim WA9YSD" <wa9ysd@yahoo.com>
To: <tentec@contesting.com>
Sent: Tuesday, April 07, 2009 4:20 PM
Subject: Re: [TenTec] RF Ground

> Well Gary guess you will have to dig deep into your pocket book and get 3 
> to 6 inch OD copper pipe about 12 ft long or so and go from there.  Where 
> I live the ground is moist at 8ft down in August when it is the driest, so 
> I opted to drill through the basement floor to drive  my 8 foot station 
> rods in.  You have to make your station ground as good or better than the 
> electrical ground.
> If you want your ground to be wet more dig a hole about 3 ft diameter dig 
> down about 15ft line the walls with that big city drain pipe and you have 
> a shallow well.  I will draw water towards the well and keep your station 
> ground damp.
> Keep The Faith, Jim K9TF/WA9YSD
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