anything better than a PolyPhaser

[Mikey]

I have a PolyPhaser lightning arrester that i suspect is bad, is there any good way to test these and tell if they have taken a hit or are bad? Also i'm not too impressed with the PolyPhaser, is there a good alternative that is recommended. THis is going on a public safety repeater at 50 watts VHF. Thanks

Mikey

[Jim202]

Most Polyphasers use a gas tube for the protection of high voltage surges. Problem is that over time the voltage fire point will gradually go lower. In other words it will start to fire with a lower voltage after each surge that it protects the equipment from.

The only way to test the protectors is with a variable high voltage power supply. You gradually raise up the voltage to the trip point. You watch the voltage that it fires at. like I said before, each time the gas tube fires, the next time will be at a slightly lower voltage.

As far as another surge protector, you could use the dead short type unit, but they are frequency dependent. Unlike the Polyphasers that cover a rather wide range of frequencies, the dead short unit has to be made for a very narrow frequency range.

No matter what you use, you need a good low impeadance ground to work with the surge protector.

Jim

I have a PolyPhaser lightning arrester that i suspect is bad, is there any good way to test these and tell if they have taken a hit or are bad? Also i'm not too impressed with the PolyPhaser, is there a good alternative that is recommended. THis is going on a public safety repeater at 50 watts VHF. Thanks

Mikey

[Bruce1807]

The whole concept is self sacrificing if need be.
Sometimes they do their job and survive and other times they are destroyed.
The important thing is that the actual polyphaser is grounded.
So many sites I’ve seen with the polyphasers hanging on a cable in mid air, no ground wire.
I have all mine mounted in an Andrews trapeze made just for the job.
Apart from that it makes my 18 cables look neat,
If it’s public safety and it’s had a hit.
Replace it, simple as that

[Mikey]

But that's just it, how do you know if it has taken a hit or not? Is there a good way of testing it?

Mikey

[Bruce1807]

Are you in a heavy lightning area.
Is the tower and equipment installed to /\/\'s R56 standard?

Have a look at the pins and see if they are black or heavily tarnished.
if so replace.
I assume the station works no different with it inline or removed.
Like I said if you think you took a hit just replace it, especially for public safety. They are not very expensive.

I throw all mine out every two years no matter what.
It works out about $8000.00 a pop but then I'm responsible for a PS system in the hurricanne belt. I also have strike counters on each tower so I know when we take a hit.

This was sort of to mitigate what happened several years ago when I lost 12 quantar contoller boards in the flash of a second.

[xmo]

Mikey: "But that's just it, how do you know if it has taken a hit or not? Is there a good way of testing it?"
_____________________________________________________________

I looked around Polyphaser's web site but I did not find a recommendation for a field testing procedure. I think the issue warrants a phone call to one of their application engineers.

The RF characteristics of these devices can be verified on a network analyzer [i.e. insertion loss & VSWR / return loss]

Non-destructive testing the of their protective characteristics may be as easy as this:

http://www.transient.se/frame/4010-01.html

"Bourns 4010-01 Surge Protector Test Set is a hand-held, battery-operated tester designed to measure the clamping voltage and dc breakdown voltage of most surge protective devices."

Should be less than $800.00

[Mikey]

Thanks for all the reply's, i had a problem with the paging repeater last night and when i went and pulled the polyphaser out of line it cleared the static and coverage issue right up; now we haven't had any electrical storms for a while now so i was just wondering if it had taken a hit and then slowly degraded itself until it was noticeable on the channel. When i checked the Equiptment side of the polyphaser it was shorted to the outer connector, and when i checked the center pin straight thru, no continuity. Was just wondering how many more polyphaser's were on the brink of crapping out on me. Again thanks for all the help.

Mikey

[Bruce1807]

What has probably happened is it took a hit and the heat degraded one of ther solder joints.
A bit of vibrastion,temperatre changes etc. and it finally failed.
If it's one that you can open you'll probably see the problem.
At the end of the day it sound like it took a hit and did it's job.
Time for a new one.

[Jim202]

Mikey, You evedently didn't pay any attention to my post about the degrading of a Polyphaser. The firing point goes down after every time they fire.

In your case with the paging transmitter, it was causing enough voltage from the RF power to cause the surge protector to start to fire. This caused the noise your pointing out that went away when you removed the Polyphaser.

Polyphaser does have a tester to check out their devices. But again I point out that anytime you apply a voltage that causes them to conduct, it lowers the next trip point. Kind of like a self destructing testing.

As you also found out, you can't measure continuity between input and output. In most cases, you can't do any coax cable TDR or sweep testing through them. Have seen many a field tech go down in flames over these simple issues.

Jim

Thanks for all the reply's, i had a problem with the paging repeater last night and when i went and pulled the polyphaser out of line it cleared the static and coverage issue right up;
Mikey

[davidguy1973]

Polyphasers from what I have experienced are like the others have mentioned a one time use. The serve their prpose of sacraficing themselves before they strike reaches the equipment. Usually suggested once they take a hit replace them. For testing issue usually a wattmeter in line checking reflection will identify your issue. A high reflection with polyphaser in line and no reflection with polyphaser taken out of line will indicate a replacement of the polyphaser. Paying for one polyphaser is checaper than the damage with out one. This what they are designed for.

[RFdude]

It is very generic and easy to say replace it every couple of years. But in today's cash strapped reality, it may not be fiscally responsible. I'd rather apply that $8000 per year towards justification for a handheld sweep analyzer. You must already sweep all your antenna's every year during PM, so you can do so with the Polyphasor in line and check both. If things look below your spec (18 dB RL or so) you can take a closer look at the Polyphasor vs antenna to try and isolate the issue.

The life of a Polyphasor also depends if your system is multi-coupled or not. Is your antenna in the near field of other antennas? Not every Polyphasor is recommended for a multicoupled tx line or at a site with lots of other near field emitters. The surge device might sweep well, but create lots of noise or IMD under strong RF conditions. This sort of behavior requires investigating the entire antenna system too.

For all but the highest power Polyphasors, you can use a 1000V Megger to test the breakdown voltage. I've also used the photoflash units from a throw away camera. Wire the protection DUT in parallel with the photoflash capacitor and a MAX/MIN digital voltmeter. The meter in MAX mode will display the voltage at which the tube fires and MIN will display the voltage at which the arc extinguishes. The cost of this high voltage source is almost free. After repeated... (its fun )... testing, I see no difference with the tube firing voltage.

My understanding of the gas tube end of life is that the electrodes in the gas tube sputter during arcing. The sputter and vapourized metal is deposited onto the cool tube envelope. This is how IMD can come to life or how the tube characteritics can change.

RF Dude

[Bob W]

For testing issue usually a wattmeter in line checking reflection will identify your issue. A high reflection with polyphaser in line and no reflection with polyphaser taken out of line will indicate a replacement of the polyphaser.

I disagree. Depending on the mode of failure, that may work. If the coupling capacitor opens, the meter will show it. If the coupling capacitor gets hit hard enough to short, everything looks fine RF wise. It can be a source of noise. If the gas tube gets hit hard enough to develop a crack, everything looks OK RF wise. Take a look at my pics of a polyphaser that got hit hard. http://batboard.batlabs.com/viewtopic.p ... highlight=