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Author Topic: Surge Protection.  (Read 712 times)
KE5BTA
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Posts: 14


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« on: September 16, 2004, 04:35:02 PM »

I was happening across some catalog stuff (just browsing, you know) and I noticed MFJ puts out a product called the Lightning Surge Protector (MFJ-270).  You hook it inline with your antenna feeds and it supposedly pops on a surge.  Can this really protect against a lightning strike?  I can't imagine that a lightning hit would just magically stop right at this device then divert to ground without still damaging anything else hooked up to it.

Worthy investment?  Pipe Dream?

73,

Brando
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WB2WIK
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Posts: 20560




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« Reply #1 on: September 16, 2004, 05:26:53 PM »

It isn't intended to stop a direct lightning strike dead in its tracks, that is a pipe dream.  But it doesn't claim that, either.

This is a gas-discharge transient protection device which fires when the surge voltage exceeds some predetermined level.  It protects against high levels of static electricity and some electromagnetic pulses which result from "nearby" lightning strikes, not direct hits.

Still, this is very useful protection since a direct hit is much more rare than an indirect one.


Alpha-Delta Communications has had their "Transi-Trap" devices on the market for decades (http://www.alphadeltacom.com/tt3g50.html), long before the MFJ product, to do the same thing.

One problem with these little protectors is that in order to fire at a sufficiently low voltage to actually protect equipment, they cannot handle a lot of transmitting power (or the transmitting RF voltage will fire them, instead).  So, most of these devices are rated for low power operation (maybe 200W or so) only.  If you run 1500W output, especially under some mismatch conditions, you could be in trouble with almost any of the gas-discharge protectors.

WB2WIK/6
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OCEANARADIO
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Posts: 7


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« Reply #2 on: October 07, 2004, 10:55:11 PM »

Now that you have survived another lightning season, I recommend making use of the mild fall weather to design a safe station grounding and lightning protection system.

In this respect, it's really all or nothing; you either disconnect everything before every thunderstorm, or protect everything. Anything in between can invite damage, or worse.

I have to operate during storms in a high lightning rate area, so rather than add to the good comments already made, I will offer my research and plans in a the website form first:

http://members.cox.net/pc-usa/station/grounding.htm

Always happy to answer any questions and learn something new along the way.

73,

Jack
Va Beach

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K9KJM
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Posts: 2416




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« Reply #3 on: October 14, 2004, 11:48:25 PM »

I have studied PROPER lightning protection on commercial radio systems for over 30 years now. By FAR the best explaination of what to do is posted right here on Eham .......
http://members.cox.net/pc-usa/station/ground0.htm

Crawl out from under the bed during storms and follow this advice!
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