Forum

I have seen a bunch of different LAR's with different specs, and I was hoping someone could shed some light on the value that differences.

0-3 GHz 90 V Lightning Protector
0-3 GHz 350 V Lightning Protector
0-3 GHz 600 V Lightning Protector

0-6 GHz 90V Lightning Protector

Obviously we all know what the first numbers are, but what about the second numbers. Data sheets say "Gas Tube Breakdown Voltage"..can someone explain that?

Which do you think we should go with?

Thanks

~K

Hi Snag

Good question.

The term comes from the practice of using a special gas in a small metal tube, electrically connected to the antenna cabling [ co-ax usually ]. Normally the gas does not conduct an electrical current, and is to all intents and purposes an open circuit. In other words, it is as if it is not there.

When lightning occurs, an electromagnetic wave is radiated outwards, and currents can be induced in electrical conductors. These currents can be enormous. They are usually called transient currents. They can cause great damage. When the voltage across the device reaches a certain value [ the 90 volts etc ], the gas ???¡é?¡é?????¡­?¡°breaks down???¡é?¡é???????? and ionizes. When this occurs, the device conducts and ???¡é?¡é?????¡­?¡°shunts???¡é?¡é???????? the current to earth, hopefully protecting the radios etc. Depending on the application, some devices may not use gas.

But it???¡é?¡é?????¡é???¡és not quite as simple as this. When the currents begin, they may rise in value very sharply or may gradually increase. We call this the dV/dt [ differential rate of voltage versus time ] value . Some devices cannot cope with a very sharp spike and end up not conducting???¡é?¡é???????|.not good. When the device has been hit a few times, it might not even work, and us none the wiser !! We might think ???¡é?¡é?????¡­?¡°Well use the lowest value???¡é?¡é????????. In this case, we might have a few mild strikes nearby causing the device to fail, then when a ???¡é?¡é?????¡­?¡°big one???¡é?¡é???????? comes along, there is no protection !!

It can get complicated. I suggest calling these guys They???¡é?¡é?????¡é???¡ére world leaders in this. I don???¡é?¡é?????¡é???¡ét want to comment on which one as a lot of money can be at stake in this and I don???¡é?¡é?????¡é???¡ét want an irrate phone call at two in the morning ???¡é?¡é?????¡­?¡°Oy???¡é?¡é???????|you told me to get ???¡é?¡é???????|???¡é?¡é???????|???¡é?¡é???????|.???¡é?¡é????????

http://www.polyphaser.com/techdocs
Tons of good stuff there.

Bye the way, lightning protection and grounding are an art as well as a science. Lightning is one of the most complex things on the planet, and does not always behave as we imagine it should.


http://www.polyphaser.com/techdocs/Lightning%20Overview.pdf


Dave