[TowerTalk] Fwd: Near Field Lightning Damage

Sun Apr 19 20:30:41 EDT 2015

A comment on digital watches. Most I've seen used for sports and 
aviation were in the $50-$60 range with plastic cases  I have two new 
ones that are almost all plastic.  Admittedly, they are not "top end" 
watches, but they are typical.

I agree with the cage thoughts unless the EMP was quite strong.

As to nearby strikes.  My tower took at least 17 visually verified 
direct hits over 6 years with no equipment damage except for some coax 
connectors losing their plating, yet none in the last 6 years. 
Unfortunately, my wired, gigabit CAT5 network was fried last summer from 
a strike nearby?  The question mark is because I know of nothing really 
close, BUT There are two, 130' runs from the router/switch to the shop 
and one about 25' long to my wife's office in the other direction.  Both 
the router and switch were dead, the integral NICs in 3 computers have 
never been the same and an additional computer was a complete rebuild. 
The only things still good were the 850 W PS and the 4 internal HDs.

I've since added a 16 TB NAS with a 26 TB soon to follow, but I need to 
change from PVC conduit to EMT conduit, or go to shielded CAT6 (or 
both).  It's difficult to disconnect all 5 computers, the router/switch, 
modem and the NAS when ever I'm not using them as a restart involves 
multiple trips between the house and shop. If I disconnect them when I 
hear a storm approaching, it can get pretty frantic by the time I 
finish.  I could go to static IPs which might save one trip.  Soon both 
stations and two TVs will also be on the network which will necessitate 
static IPs although they could be wireless except the two stations.

I have a similar problem with SO2R operation as the two stations (one in 
the house and one in the shop) are on different electrical feeds.  I 
need to verify that they have the phases wired the same as I've fried 
the matching networks in two large duo band UHF/VHF verticals and the 
finals in the two rigs connected to those antennas..
The two HF stations use the same antenna system through a 6 pack which 
needs to be expanded to handle more antennas
Of course that ties the ground system for both stations together and 
that ties the grounds for two breaker panels together.  I see no way to 
avoid that.

73

Roger (K8RI)

On 4/19/2015 3:44 PM, Hans Hammarquist via TowerTalk wrote:
> This sounds very anecdotal. Yes, a near strike lightning may take out CB
radios etc but that it took out digital watches make me suspicious. The are
usually metal encapsulated and very immune to external field. I believe a
EMP strong enough to take out a watch also will take out the person 
carrying
that watch.
>
>
> Depending on the grid size, a Faraday cage is useful for the EM from a
lightning as the "M" will introduce back EMF in the cage which will
neutralize the "M".
>
>
> I hope the "falme" will not be too long,
>
>
> Hans - N2JFS
>
>
>
> -----Original Message-----
> From: Patrick Greenlee <patrick_g at windstream.net>
> To: towertalk <towertalk at contesting.com>
> Sent: Sat, Apr 18, 2015 10:18 pm
> Subject: Re: [TowerTalk] Near Field Lightning Damage
>
>
> Back in the 80's a tuna boat pulled into San Diego with every device on
> board
> containing a semi-conductor inoperative.  CB radio, Marine VHF,
> SSB, SONAR,
> RADAR, VHS tape player, SatNav LORAN, and on and on...  All
> the crew members
> wore digital watches which were all totally dead.
>
> One near miss by a large
> lightning stroke took out everything with solid
> state semiconductor junctions.
> The good news was they didn't have a
> spotter chopper aloft at the time
> dependent on the aircraft beacon band
> transmitter on board to find the boat
> (helipad is the roof of the pilot
> house.)  We theorized it was the EMP that
> ate everything as there was no
> evidence that the bolt hit the boat.
>
> Later
> when asked what could be done to provide an immune backup comm
> radio we told
> them a mu metal box.  A Faraday cage wouldn't stop the
> magnetic pulse.
>
> Just
> a thought in case there are any serious preppers in our midst.
>
> Patrick
> NJ5G
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-- 

73

Roger (K8RI)

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