Hi Jeff,
I just want to say that I agree with all what you say (write) about lightning
protection. Really worth reading
Hans - N2JFS
-----Original Message-----
From: jeff millar <wa1hco@wa1hco.net>
To: taholmes160 <taholmes160@gmail.com>
Cc: Tower Talk <towertalk@contesting.com>
Sent: Mon, May 9, 2016 11:51 pm
Subject: Re: [TowerTalk] Coax Grounding
Hi Tim...
I'll take a shot at this.
- Ground rods are a standard practice but they don't really do much when
typical lighting current hits 1 to 100 KiloAmps
- 1 ohm ground rod and 1 KA is still 1000V...and real ground rods are
not that good
- Mountain top installation use a ground grid with many ground rods,
but they still mount the equipment on a wooden platform to prevent arcing
to the concrete
- The real trick is to bond the coax shields, AC power ground, and any
phone or internet to a common ground plate
- Mountain top installation use a large copper plate with all the AC
outlets, Modems, Coax feedthru, etc on the plate
- They also wrap the room near the floor and ceiling with a ring of
copper bus to keep everything a the same potential
- The idea is to admit that the shack will jump to 10 KV above ground
on a strike, but to ensure it all jumps together
- Keep that in mind as you sit at the radio with your feet on the
floor and headphones on your head
- For an amateur installation, run the coax to a common bus bar and
connect that bus to the Rig ground stud with wide flat cable
- The flash tube lighting arrestor is good for dipoles that do not have
a good DC connection from center conductor to ground
- I recall seeing sparks jump to the concrete floor from the center
pin of a PL-259. It was connected to an 80M dipole. The sparks jumped
about every second.
- For many beams, the center conductor is a good DC ground for the
KHz and low MHz lighting frequencies
- There are two types of lightning in the shack to worry about
- 1) Comes in the tower and goes out to the ground, water pipe, well,
power ground, etc.
- 2) Comes in via the power line, cable line, water pipe, etc. and
then goes out through the feedlines and tower
- The tower is a good radiator for fast rise time energy entering
the house
- I lost a bunch of stuff when the house down the street was hit.
(chimney, blew the clean-out door across the room)
- Anything with a long wire connected to the power failed: Radios,
telephone, door bell transformer, garage door opener,
thermostat transformer
- Also a 8 inch diameter plasma burn on the outside of the house,
opposite where romex was coiled for spare circuit
jeff, wa1hco
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|