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Author Topic: A long wire lightning arrestor?  (Read 2973 times)
WALTERB
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Posts: 528




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« on: April 05, 2013, 01:49:03 PM »


In a nutshell I’m wondering if I can have as much protection on a long wire as I can with my coax?
Here is one product.

http://www.arraysolutions.com/Products/AS-309H.htm

The long wire is for my DIY crystal radio (receive only) , so I don’t have a lot of money tied up in it, however I don’t want to invite lighting into the shack either.
 
A knife switch is doable, provided it would actually do something other than give me a warm and fuzzy.  Grin

Disconnecting inside the shack and throwing the line out into the yard isn’t realistic given the hassle of running the wire from the grounding system into the shack in the basement.

thanks.
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AA4PB
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« Reply #1 on: April 05, 2013, 02:06:11 PM »

You could probably get away with one of your coaxial arrestors on a long wire that is used for receive only. There will never be much voltage present during receive. You sill need a good ground connection on the arrestor however.
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WALTERB
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Posts: 528




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« Reply #2 on: April 05, 2013, 02:11:56 PM »

You could probably get away with one of your coaxial arrestors on a long wire that is used for receive only. There will never be much voltage present during receive. You sill need a good ground connection on the arrestor however.


thanks. Originally I tried using my OCF dipole's coax as the antenna for the crystal set but I got nothing.  I assume it had to do with an impedence mismatch or something considering it had a 4:1 balun.  I actually got better reception using the spool of project wire as the antenna than I did with my OCF thats up at 43 feet.  I tried hooking it up to the center, tried the shield,  tried hooking another 4:1 balun up in reverse in the shack,  nothing worked.  Thats why I ran the long wire.   I guess your idea should work since its not unblancing the line.

thanks.


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WB6BYU
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Posts: 13170




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« Reply #3 on: April 05, 2013, 03:21:07 PM »

My grandparents had a fancy device on the wire antenna to their old Scott
receiver:  basically a neon bulb in a glass case that would conduct when
the static build-up on the wire got over 75V or so.

But none of those will really protect you from a direct hit on your wire, which
can result in thousands of amps (until the wire melts).  That's the stuff you
really don't want flowing down a thin ground wire from your shack to the
basement!
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WALTERB
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Posts: 528




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« Reply #4 on: April 05, 2013, 03:33:29 PM »

My grandparents had a fancy device on the wire antenna to their old Scott
receiver:  basically a neon bulb in a glass case that would conduct when
the static build-up on the wire got over 75V or so.

But none of those will really protect you from a direct hit on your wire, which
can result in thousands of amps (until the wire melts).  That's the stuff you
really don't want flowing down a thin ground wire from your shack to the
basement!

yes, I agree. I believe the setup I have currently for my ham shack works well.
The lightning would have to travel down the coax,  and the last 5 feet its wrapped around a copper clad grounding rod that is connected to
the Universal Common Grounding System (UCGS) I have for the entire house (electrical, ham shack, antennas, etc.)
The lightning would then have to travel underground 30 feet, travel up to the copper buss where the coax is grounded outside the shack, then travel back into the shack via conduit that also carries the shack grounding buss strap back out to the same copper buss it just came from.  the lightning would then have to enter my basement ham shack and hit the Polyphasers on the shack bus, then travel up the coax and hit my rig(s) that are also grounded back to the UCGS.   Not saying it wouldn't happen, which is why I have home owners insurance, but if this setup doesn't stop damage then I need to take up stamp collecting or something.  Grin
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K0ZN
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« Reply #5 on: April 05, 2013, 03:41:48 PM »

For a receive-only application there are several things you can do.  If you just want to bleed static electricity off the antenna, string of
several 2 watt resistors, totaling about 30K ohms connected to ground will work quite well; the amount of resistance is not critical....all you need
is enough that it doesn't attenuate the received signal. The least R you could use would be the best case and you can experiment to find that value.  
You could also make a homebrew RF choke....or some combination of resistors and an RF choke, then shunt that with a homebrew spark gap with about 1/8" space in the gap.

If you want REAL lightning protection, you still absolutely must have a GOOD earth ground system of at least 2 to 3 ground rods and heavy conductor to the arrestor gap.
For a receiving application, I would sure consider the homebrew route first. You can also short the antenna to the ground system via a switch
or jumper if a storm is in the area. Again, if you want good lightning protection, you should also connect your ground to your AC power line entrance ground.

You also could use a commercial protector device if you wanted but that is probably a little more costly.

73,  K0ZN
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W8JX
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Posts: 5678




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« Reply #6 on: April 05, 2013, 04:20:36 PM »

You could also use a large spark plug at the terminated end of antenna that is bolted to a fixture that is grounded. I would no effect high impedance voltages that can reach several hundred volts on a open wire.
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W8ATA
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Posts: 321




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« Reply #7 on: April 06, 2013, 07:41:37 AM »

Well I have been in a lot of jails and have never seen any lightning that has been arrested.  Wink As has been well pointed out, we do other things to minimize damage like with surge protectors and grounding. I have a long wire antenna for my Icom 7000 and  despite lots of grounding I disconnect it and direct it to ground by a big ceramic base knife switch when any electrical storm activity is within 30 miles. I wish manufactures and suppliers would stop using the term "lightning arrestor" when most are just a static bleed spark gap. When lightning is truly arrested pigs will fly at Mach I.

73,
Russ
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AA4PB
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« Reply #8 on: April 06, 2013, 08:03:08 AM »

What I was referring to with the coaxial type of arrestor was NOT to feed it with coax or try to use it with an OCF dipole. It was to simply break the long wire feed and connect it to the center conductosr of the coax connectors and ground the frame. That will limit the voltage between the long wire and ground to a fairly low value. It wouldn't work for a transmit antenna because the wire could have some high voltages during transmit that would break down the arrestor. For receive however it should work just fine.
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WA3SKN
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« Reply #9 on: April 08, 2013, 03:34:08 PM »

Get yourself a knife switch and mount it outside, keep it grounded (to an outside ground) when not in use.  The spark plug deal was popular with the old tube rigs and open wire, but they found out that transistor rigs would fail before the gap was bridged... so it went out-of-favor.
And try to design it so the static buildup will not drain through the recveivers input coil.  It will be a lot quieter listening!
73s.

-Mike.
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W8JX
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Posts: 5678




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« Reply #10 on: April 08, 2013, 06:55:28 PM »

Get yourself a knife switch and mount it outside, keep it grounded (to an outside ground) when not in use.  The spark plug deal was popular with the old tube rigs and open wire, but they found out that transistor rigs would fail before the gap was bridged... so it went out-of-favor.
And try to design it so the static buildup will not drain through the recveivers input coil.  It will be a lot quieter listening!
73s.

-Mike.

I still like the idea or a spark plug type device at far end of wire in addition to any device on receiver end as it give a second path for energy in a direct hit.
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KH2G
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Posts: 261




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« Reply #11 on: April 11, 2013, 04:24:46 PM »

A well grounded spark plug does work well but you need to put a plastic cap or some kind of bug cover so a bee or whatever doesn't make a home between the contacts.
Enjoy
Dick KH2G
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G8JNJ
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Posts: 487


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« Reply #12 on: April 12, 2013, 12:51:33 AM »

Hi,

The voltage developed on a long wire type antenna tends to build up over a period of time (not a direct strike !). Once it reaches a sufficiently high enough potential. It will discharge across whatever it finds to be the weakest link. This could be an antenna connector, neon discharge tube or spark gap.

For a simple receive only application like this. You only need to add something like a 1/2 watt 100K resistor between the end of the long wire and ground. This helps provides a static discharge path to earth, Which stops the voltage building up in the first place.

As an aside it's interesting connecting a digital voltmeter between ground and a long wire antenna. I've noticed huge variations in the level and polarity of static charge.

That's why it's always a good idea to briefly put a short across an antenna connector, before attaching an expensive antenna analyser.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com

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