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@windstream.net>
To: towertalk <towertalk@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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