[Elecraft] Lightning season is on the way in New Mexico.
Mel Farrer
farrerfolks at yahoo.com
Mon Mar 28 20:49:39 EDT 2011
All of this is of course, very good advice. I would like to add a little humor
experience driving through the southwest on the way back to my post at Fort
Gordon, GA.
I left CA and went to the southern route to GA which took me to Flagstaff, AZ
and east. While on the way, I had my 6 meter antenna on the back of my 1957
Chev convertible and the rig unconnected in the back seat. While driving
across the desert, in the afternoon while the overhead storm was obvious, I
heard some snapping sounds, but could not find a source. I stopped for dinner
and got back in the car to continue...... After a while I heard the snapping
sound again. But everything still seemed fine. When the light faded and the
sky darken, the snapping sound was accompanied by a flash in the car. I pulled
off and looked around when it flashed again, it was the end of the coax
connector and the static electricity was arcing across the end of the
connector. I piece of gum wrapper across the end stopped the arcing and I
continued to Ft. Gordon at ease.
Mel, K6KBE
________________________________
From: FredJensen <k6dgw at foothill.net>
To: Elecraft Reflector <elecraft at mailman.qth.net>
Sent: Mon, March 28, 2011 4:39:36 PM
Subject: Re: [Elecraft] Lightning season is on the way in New Mexico.
Grounding and lightning protection is not a simple subject Phil. Here's
what I would recommend:
If your home is wired to NEC standards, the neutral [center-tap on the
pole pig] will be tied to the safety ground [green wire in your outlets]
and earth at the service entrance ... only. This means that the "green
wire" in each outlet snakes back to the service entrance before
encountering a "real" ground. It thus makes a useless RF ground and
lightning is RF [see below].
A. You *must* tie your ground rod back to the ground at the entrance
panel. NEC requires it and if it isn't so tied, it can create a real
safety hazard if you should encounter a ground fault. Make it as short
as possible, buried is best, but if short means run under the house,
that's OK. Use #14 copper or larger.
B. AC is excluded from the inside of a conductor by the magnetic field
it creates, and flows near the surface [skin] effect]. The higher the
frequency, the closer to the surface it is. The conductors on one of
the original 230 KV lines from Hoover Dam to Los Angeles are hollow for
that reason.
C. Lightning currents are mainly RF, and flow only on the very surface
of the conductor and you want a lot of surface area, volume contributes
almost nothing. So, wide copper strap is good. Large gauge stranded
copper wire is less effective but better than solid wire. For the fire
lookouts on peaks here in the Sierra Nevada, they use 3/8" - 1/2"
stranded wire running around the roof, catwalks, and tower legs, bonded
to everything including an extensive ground system.
D. Surviving a direct hit to your tower or antenna is problematical at
best. Even if you disconnect and ground your antenna [and rotator]
cables, the induced currents will create high peak potentials to your
equipment [and everything else in the house]. You can't stop that from
happening, and your radio chassis can momentarily rise to very high
potentials.The grounding goal for your equipment is to "keep it all
together." The radio chassis can experience a peak pulse, but if
everything else also gets that same pulse, the differential potential
between them is very low, and little current will flow. The way you do
this is to bring your ground strap into the shack, and using the
shortest wiring you can, ground *each* piece of equipment *separately*
to the same point on the strap.
E. A grounded entrance panel for your coax and rotator cables is very
good, use Polyphasers or similar to bring the cables through. They
won't survive a direct hit, but in that case, that's the least of your
worries, your house may be on fire by then. :-( They will clamp off
induced pulses however and limit potential excursions on your equipment.
F. Unless your home is on stilts over salt water [unlikely in NM :-) ]
I'd guess that your ground rod is probably pretty high impedance for any
currents generated by lightning. At the TV station I worked at in
college [500' tower on a 1,300' ridge], the ground system ran all
around the building with a bunch of ground rods, and included things
like the tower, the fridge, plumbing, the 3 1/8" hard-line exterior,
even the gate on the road, and the steel trench covers inside, They
still made a deafening "clang" when we took a nearby strike. Hams do
install systems like that around their houses, it's expensive and it's
really a trade off with risk.
G. If you have an Elecraft rig, you're covered. If you don't, make
sure there's a bleed [RF choke or high value resistor] across the
antenna connector. Precip static can sound innocuous if annoying, but
without the bleed, it can store charge in the input circuit and
ultimately cream it. We killed 2 IC-756PRO II's in 2009 from this in a
snowstorm during the Cal QSO Party in Alpine County.
If you have any specific questions, I'd recommend first contacting Jim,
K9YC [who is really near Santa Cruz CA]. He has a wealth of information
and tutorials on his web site. The grandson of Art, my Elmer of 57
years ago, W6RMK, now holds his grandad's call and has made his living
as a lightning expert. If some question comes up, I'll be glad to take
it to him. This pretty much exhausts my knowledge.
73,
Fred K6DGW
Auburn CA
On 3/28/2011 9:35 PM, Phil Townsend wrote:
> Lightning question:
>
> I have driven an 8 foot copper clad rod just out side my operating station. Its
>about 6 feet from the rod to my desk.
> I have attached a solid copper wire (1/4" thick) to the ground post (with a
>ground rod clamp) The wire goes thru the wall and is bonded to a copper pipe
>that is 1-1/8" wide that is just under the desk.
>
> So on to my question:
> What is the BEST way to connect my equipment (k3, SB-200 and a remote coax
>switch) to the copper pipe?
>
> Coax braid from RG8 or solid copper wire? and why....
>
>
> Thank You guys...
>
> Phil
> Santa Fe
>
> soon to be a xx5SSR...
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