[TowerTalk] Lightning Arrestors

[jimlux]

Doug Rehman wrote:
> Let me preface this with INAE (I'm Not An Engineer...); the below is based
> on my practical experience in both public safety and amateur communications.
> It is also based on the commonly seen protectors from ICE and Polyphaser.
> 
> As to which is "best", there are a lot of factors to consider and what is
> "best" for one application isn't for another. I use a mix of ICE and
> Polyphasers.
> 
> I have far more Polyphasers in service since new ones are often available on
> eBay for a steep discount.

Just curious, why do you think that is?  Is it some sort of marketing 
approach from PP?  I would readily believe that PP's "factory direct" 
price is greater than the retail store price (PP wants to encourage 
their retailers and distributors, so they protect their pricing)


> 
> In my previous life overseeing the communications system for a state law
> enforcement agency in Florida, I had Polyphasers installed on all of our
> feedlines (remote control phone circuits and power too). This reduced the
> summertime lightning damage from taking out a station about every other week
> or so to only one or two stations per year. 

Were the damage events from direct strikes or from induced transients 
from nearby strikes?


> 
> At least in the US, Polyphasers are used far more than any other brand in
> commercial/government VHF/UHF applications. 
> 
> Pay attention to the frequency and power ratings- you don't want to fire the
> gas discharge tube with your RF. Also take into consideration the VSWR of
> the antenna- an unmatched antenna could cause the voltage in the protector
> to go high enough to fire the tube even though the transmitter output power
> is under the rated maximum.
> 
> For antennas with the potential for induced static charges (wind, lightning,
> etc.), I use ICE protectors since the center conductor is at DC ground.
> Since the Polyphasers are not at DC ground, the static charge will build
> until it crosses the threshold for the gas tube to fire. In an installation
> where static charge is a significant problem, the life of the protector
> could be diminished by the continual firing to dissipate the static charge.

Gas tube type protectors should have almost infinite "fire event" life 
(e.g. a NE2 bulb fires 120 times a second when hooked up to the AC line)

Thyristor based suppressors definitely have limited life.

> 
> Don't forget protectors for other wires coming into the shack such as the
> rotator cable. You can find commercial products or just put MOV's across
> each line to ground. (All of the commercial protectors I have looked at are
> simply using MOV's- you're paying for the nice packaging.)


Be careful of the parallel C of MOVs on high speed data.

Shunt suppressors (gas tube and MOV type) also have an "interesting" 
aspect that they can actually induce a transient downstream when they 
fire. (the magnetic field from the fast di/dt on the source side when it 
fires couples into the downstream side).