[RFI] Lightning Protection

[EDWARDS, EDDIE J]

" I see the diasharge brushes on remote sites, radar, repeaters, surveillance, 
even airports surrounded by towers with brush arrays a few tens of feet 
across?"

"Not effective at all?  What about a row of air terminals on a house?"

Motorola's R56 grounding standard for comm sites does cover air terminals (not brushes though):

"The use of air terminals (lightning rods) on a tower may be appropriate in some circumstances to protect
antennas from a direct lightning strike. If the tower is over 45.7 m (150 ft.) tall, side-mounted antennas
are vulnerable to direct lightning strikes. Side-mounted antennas installed at a height greater than
45.7 m (150 ft.) may be protected through the use of horizontal lightning rods. The horizontal lightning
rods are attached to the tower, just above and below the antenna."  

So it's an attempt to absorb the strike, not prevent it.  And they also show them used on building roof tops probably to meet NEC code. 

In Roger Block's (PolyPhaser's) "The Grounds for Lightning and EMP Protection" (no longer published), there is a reference to a US Navy report and FAA video, but no report numbers or specifics:

"A US Navy report, done in cooperation with the USAF, NOAA, and the FAA, states that after several years of study, brushes have not prevented any lightning strikes.  (If they worked, NASA would be using them extensively.)  The FAA even did another study on the brushes and have video tapes showing them being hit again!"

I have witnessed a broadcast tower being hit that had the "brushed-ring" mounted on top of the tower/antenna.  It was the only one in the area that had a brushed-ring.  So it didn't seem to work from my perspective.

Some articles on lightning have claimed that some of the steel-brush air terminals on radio towers have ended up causing fires when the melted steel from the brushes fell onto flammable or dry materials.  However, no examples were given.  Seems plausible though.  

73, de ed -K0iL

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On Behalf Of KD7JYK DM09
Sent: Sunday, July 01, 2012 11:22 PM
To: rfi at contesting.com; Kim Elmore
Subject: Re: [RFI] Lightning Protection

"I asked them about these corona brushes and was told that they are 
ineffective. Once the electric field exceeds about 50-100 kV per meter, 
everything -- grass, trees, fences, antennas -- are all in corona and the 
air is about as "saturated" with corona ionization as it can get. These 
corona brushes have no effect"

Several of htese at a site won't lower the potential in the immediate area 
preventing charges in the 50-100 kV per meter range?

I see the diasharge brushes on remote sites, radar, repeaters, surveillance, 
even airports surrounded by towers with brush arrays a few tens of feet 
across?

Not effective at all?  What about a row of air teminals on a house?

Kurt

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