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Should the radials be buried as well or just spread out in a direction
away from the house

Brian Mackey
KC1MAC/AG
Hams don't let hams get stuck on 2 meter repeaters!

From:
Reply-To:
Date: Thursday, January 9, 2014 at 9:07 PM
To:
Subject: Re: [IC-7000] Lightning Protection References

Brian,

I agree that approach has several problems, which are easily corrected.
Without knowing the details of how long the coax, ground wires, etc. it is
hard to quantify the degree of the problem.

1. A single ground rod can easily saturate the surrounding ground, at which
point the charge remaining on the coax continues on directly to the radio.

2. Since the radio is connected to a separate ground rod, which is at a low
earth potential (assuming it is some distance from the antenna's ground
rod), all of the remaining current on the coax flows through the radio or
tuner chassis en route to the "radio" ground rod.

3. It is likely the coax entering the structure will have a high enough
voltage on the shield to arc over to nearby objects during an average strike
of 18,000 amps and 2 microsecond rise time. Even outside, the coax can arc
over to nearby objects, creating pinholes ( or worse) in the outer jacket,
allowing water in.

To correct the problem:

1. Move the lightning suppressor to the ground strip near the shack
(assuming it is outside, if not add one outside). This will divert any
induced charges generated by a nearby strike that couple into the coax from
bypassing the suppressor.

2. Use a bulkhead barrel connector where the lightning suppressor was
originally, to ground the coax shield. Mount it to a copper or stainless
steel bracket clamped to the first ground rod.

3. Connect the two ground rods with a #6 bare copper wire, buried 6" or as
deep as possible. This will reduce the dynamic surge impedance of the
ground system and be a parallel path that diverts much of the current from
the coax headed to the shack.

4. Depending on the type of soil, distance between ground rods, type of
antenna, etc., add 1 or 2 additional ground rods connected with radial
wires. Ground rods are cheap and last a long time (in most soil). The
earth isn't a very good conductor, especially at >1 MHz. See pdf page 35 in
the Polyphaser book.

5. Connect your radio ground system to the electrical panel ground, per NEC
requirements.s

Steve, W3AHL

---In ic7000@..., wrote:

On Thu, 9 Jan 2014 11:08:22 -0500, brian mackey wrote:

>> > My ground is setup where all the gear goes to a grounding strip to a
>> single
>> > 8 foot ground round, and then the antenna is grounded to a separate 8 foot
>> > ground rod (via) a lightning arrester
>
>
Very bad practice. The separate ground rods should be BONDED together,
preferably with wide copper strap. Your installation provides plenty of
area
for voltage differences.

Someone also said they used a large braid for grounding. This is another
bad
idea. Braid has plenty of inductance. Inductance at high frequencies (rise
time of the pulse) is high resistance. High resistance leads to high
voltage
between one end of it and the other. This is why solid copper grounds are
recommended. Better yet, flat copper strap. And DON'T make it look neat
with
90 degree bends in the wire, etc. It should be as straight as possible
point to
point, and when turns are needed, they need to be as gradual as possible
(low
inductance).

Gary
--
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