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).
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