[TowerTalk] Radiating Lightning Rod

Tue Jun 2 14:49:49 PDT 2009

Rick,

I did not elaborate on the tower/coax grounding, because it was not the
question. I basically just responded to the query about using a J-Pole on
top of the tower.

However, since you have raised the question, I'll provide some more detail
as to the full installation and it might be of benefit to someone. There is
nothing unique to my installation. I have just employed some things learned
along my 55 year journey as a Ham.

Grounding: The tower has a ground rod that was driven into the ground below
the Hole before the concrete was poured. This rod comes up through the
concrete and is attached to the tower legs at the base. In addition the
tower mounting framework was also driven into the ground in the bottom of
the hole. It is attached directly to each tower leg.

My Equipment box and Prop Pitch rotor are mounted about 4 ft up from the
concrete pad. The box is a double wall exterior wx proof box. It is attached
to two legs of the tower with Stainless steel saddle clamps. Also I have a
#4 stranded copper wire connecting the box to the ground rod below.

I drove a ground rod into the ground at the bottom of the house foundation
beam. This protrudes above the concrete slab about 4 inches. In addition,
the foundation concrete reinforcement steel is also bonded to this ground
rod. This rod comes up in the wall just behind my operating desk.

Coax: Each Coax going up the tower is grounded at the antenna feed point.
The three J-Pole cables are attached directly to the antenna which is bolted
directly to the Mast. The 14 element 2M beam uses a Gamma match, which has
the shield grounded. all elements are grounded to the boom. All elements on
the TH6DXX are grounded directly to the boom except the Driven element and
it is grounded at the center of the hairpin.
All coax cables on the tower are fed to a Coax feed thru on the bottom of
the metal box. Each cable has a 6-8 turn loop hanging below the box to allow
rain to drop off and not get into the connectors. Each loop is strapped to a
tower leg.
inside the box, I have inexpensive coax "spark gap" type protectors in line
with each cable. Nothing fancy here. These are inside the box With a
separate ground strap to the box grounding lug.

>From here the coax and antenna control cables goes into one of two 2in PVC
pipes that go underground to the house (100 ft). These pipes come up through
the foundation slab in the wall behind the operating desk. I also have a
coil loop in each coax on the house end and the cables are all grounded to a
common ground buss behind the desk and it goes to the ground rod in the
wall.

I do the HF antenna switching in the box on the tower to minimize the number
of cables coming to the house. I switch my HF antennas with a remote
solenoid operated rotary drum type switch. Each unused position is shorted
and I have a dummy load on the last position, which is my default setting
when I am not operating.

I think I have covered it all. I am fortunate to have designed and
personally built the house from the foundation up. Ham radio was a very key
ingredient in the design. My noise level is normally very low under this
setup. I live in the country on 5 acres, so I don't have any adjacent noise
generators.

    * 73's Jim W5IFP *

   >-----Original Message-----
   >From: towertalk-bounces at contesting.com
   >[mailto:towertalk-bounces at contesting.com]On Behalf Of Rick Stealey
   >Sent: Tuesday, June 02, 2009 1:20 PM
   >To: towertalk at contesting.com
   >Subject: Re: [TowerTalk] Radiating Lightning Rod
   >
   >
   >
   > Jim says:
   >> I run each coax to the bottom of the tower
   >> and have a 6-8 turn Coax coil on each line before it goes
   >into the equipment
   >> box at the base of the tower. from there all the antenna coax
   >and control
   >> cables go underground in PVC pipe and come up in the wall behind my
   >> operating desk.
   >
   >If there is lightning induced current coming down the coax
   >lines (in parallel with current coming down the tower legs
   >themselves) the inductance of the coil causes a large voltage
   >to appear across the coil.  This can flash to the tower easily
   >and likely destroy the coax.
   >I believe the proper thing to do is to install the coax so it
   >gets grounded right at the tower base.  In other words, assume
   >the lighting current is going to flow on the coax and we want
   >that current to get into the earth by a path that we determine.
   >Assuming in your equipment box (you didn't say) you are bonding
   >your coax lines to a good ground, then it is likely that the
   >majority of the strike current is dissipating at the tower
   >location and only a small portion will find its way to your
   >house.  But to protect the equipment in the house you really
   >should be grounding and providing lightning arrestors outside,
   >at the point where the conductors enter the house.
   >
   >Rick  K2XT
   >
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