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RE: Lightning protection



Stan :

Thank you for your very extensive advise.  I was aware of most of this when
I installed my 72 foot crankup HF tower last year.  I have the two towers'
ground screens attached to each other.  I'll be ordering the lightning
protectors shortly - still building the M-squared antennas.  I've also got
to make room on the SPG plate ;)

Thanks again,

Jamie
WB4YDL

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Stan
Sent: Tuesday, August 27, 2002 9:03 AM
To: James Hall
Cc: AMSAT-BB
Subject: Re: [amsat-bb] Lightning protection


Hello Jamie,

A few considerations:

You will never control all of the lightning strike (stroke).
You can only minimize the potential damage. The better the system,
the less will be the damage to your equipment.

Ever situation and location is different, consult a local expert.

All lightning protection systems are not a install and forget,
They must be properly designed, installed, and periodically
maintained.

One objective is to provide a metallic low impedance path away from
your equipment (and shack) for the lightning to follow.
While you will have a low impedance path thru to the shack equipment,
the lightning path must be significantly lower in impedance,
just like resistors in parallel, put the current where you want it.

Make the tower higher than the fixed satellite antenna, by ~10 feet.
now the tower is the dominant "low impedance path to ground" .


Coaxial lightning arrestors are usually:

	contacts close to each other like a spark plug,
	ie. the CHAMPION brand.

	A 1/4 wave shorted coaxial stub for the frequency of concern
	on a coaxial "T" connector. Does not pass DC on center
	conductor because of the shorted (to ground) stub.

	a gas discharge tube in a coaxial configuration,
	Like the DIAMOND brand, passes DC on the center conductor OK
	I have not taken apart a POLYPHASER unit, I believe most to
	be a gas discharge tube.
	Verify with the vendor for DC applications.

	A gas discharge tube with a 1/4 wave shorting stub at the
	frequency of concern, like the SUHNER brand, may not pass DC.
	The 1/4 wave stub is a short at DC and at lower impedance at
	other than the desired frequency.

	A more complex circuit with capacitors and inductors and the
	gas discharge tube, like the ICE brand, DOES NOT pass DC,
	and is frequency band and power range specific.


Coaxial lightning arrestors are best placed:

	at the top of the tower, bonded well to the metallic tower.

	at the vertical to horizontal transition, usually at ground
	level or elevated, bonded well to the ground system
	(earth electrode system)

	At the station (building) single point ground penetration
	point, where ALL cables enter or leave.

	As a minimum, at the building single point penetration panel


Other lightning protectors:

All other cables should be protected, like rotator control cables,
	AC power cables etc. ICE and POLYPHASER offer such devices.
	Usually MOV's that can fail open or shorted. Be sure the
	voltage specs agree with the application.


Earth electrode system:

	Minimum of a 8' ground rod, 8' from the tower base, bonded
	to the tower with a 4" solid copper ribbon, made from
	1 oz. copper flashing, from your favorite building supply house.

	Medium installation would include multiple 8' ground rods
	at the base horizontally separated by their length,
	in a line, Vee,	box or whatever configuration. All bonded
	together to the tower base with	4" copper ribbon.
	One 8' ground rod at each guy anchor,
	well bonded to each guy cable above the guying hardware,
	and bonded to the tower base. A 8" copper ribbon bonded
	between the tower base and the station single point ground,
	station penetration plate (bulkhead).

	The ultimate system would include:
		a copper mesh ground screen over the entire property,
		bonded to the tower base.

		Multiple metallic towers, much higher than the ham antennas,
		all electrically bonded together.


	Do not use copper or tinned copper braid because it deteriorates
	quickly with the acid rain and other soil conditions, use the
	solid copper ribbon.

	Be concerned with galvanic corrosion and avoid bonding
	different metals together with different metal fasteners.
	Tin the end of the copper ribbon that will be bonded to
	the galvi tower leg.

	Other factoids:

	most of the electrical continuity in soil is within the
	first few inches where conducting organic material exists.
	Mountain tops and deserts are an exception.

	Copper or copper clad steel ground rods may harm nearby trees.
	consider galvanized steel ground rods.

	do not coat the ground rods OR buried copper ribbons with bitumen

	do not put the copper ribbons or the ground rods in PVC conduit.

	consider using BENTONITE and/or COKE BREEZE, as available,
	to enhance ground rod performance.


When you have all this done, continue to disconnect and physically
isolate all ham gear from the antenna system and electrical
power system whenever a threat of lightning exists.


Stan, WA1ECF






James Hall wrote:
>
> Hello:
>
> I am designing and installing a fixed satellite antenna array on a short
> Rohn 25G tower.  After some of the most impressive lightning displays
> this past weekend - which cost 4 lives - I've been giving more serious
> thoughts to lightning protection.  On the HF array, I use Polyphaser
> gear and a substantial ground screen and single point ground.  What are
> the recommendations for this kind of setup taking into account 3 coax
> runs, 2 rotator cable runs and DC injection at the shack to power a
> downconverter ?
>
> Jamie
> WB4YDL
> ----
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