Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Safe operation during a lightning storm  (Read 3583 times)
KI4QPU
Member

Posts: 59




Ignore
« on: April 29, 2011, 08:08:56 AM »

As you well know the southeast just got hit pretty hard on the 27th with terrible storms and tornados. I was involved in a 2m skywarn net taking place locally. And I had to shut down numerous times because of lightning. Would a in house or attic antenna be safe to continue transmitting on during a bad lightning storm? If you have any ideas I would appreciate them. Those that particpate in skywarn what works for you? I can moniter on a ht but transmitting is sometimes hard to get through. Especially with excited quick keyers. Thanks in advance.
Logged
AD4U
Member

Posts: 2150




Ignore
« Reply #1 on: April 29, 2011, 08:26:17 AM »

An attic mounted antenna or an antenna inside the house would be MUCH less susceptable to being struck by lightning than an outside antenna.  However there are no guarantees.........

Dick  AD4U
Logged
K8AXW
Member

Posts: 3602




Ignore
« Reply #2 on: April 29, 2011, 08:36:18 AM »

Dick.... Would you elaborate a bit more on your answer?  I've thought about this question/answer quite a bit and have to ask, if a roof has very little attenuation to RF, certainly lightning won't "see" a roof either.

It has been my understanding that the highest grounded point in the area is theoretically the most vulnerable to a lightning strike.

As for communicating during a lightning storm, I've found that next to impossible!
Logged
KE4JOY
Member

Posts: 1316




Ignore
« Reply #3 on: April 29, 2011, 08:43:19 AM »

Safest way to operate during a lightning storm is with everything unplugged. Just make sure you don't go around unplugging. handling antenna DURING a lightning storm. The time to prepare is before. In other words dont operate during a T storm.

No an attic antenna is not 'safe' from surge. Current can be coupled inductively. It doesent have to be a direct strike. Even a close by strike can produce a tremendous [leathel] amount of current.

Lighting does not always strike the highest grounded point. It tends to take the path of least resistance. It is particularly fond of plumbing stacks, telephone lines, and your service entry. Ive even seen it course down plaster lath screening. It truly has a 'mind' of its own. Again it does not have to be a direct strike to cause damage.
Logged
AC5UP
Member

Posts: 3815




Ignore
« Reply #4 on: April 29, 2011, 09:23:31 AM »

About 20 years ago a house across the street from me was struck by lightning and it took out everything electrical short of their toaster... I lost two phones and a clock radio or two even though I was a good 150' away from the strike.

A proper lightning strike has two components: The visible ionization path of the electrical discharge - plus - a very stout electromagnetic pulse that can inductively cause secondary arcs in the damnedest places. Point here is that you don't need to be struck by lightning to be struck by lightning as my problem was the EMP from the strike across the street. One could argue there is no such thing as SAFE operating during a storm, although a proper ground system can get you very close.

The advantage an attic antenna might have is proximity to the Romex and phone wiring plus (maybe) a copper pipe or two. This may offer alternate discharge paths while being much less attractive than a monopole standing tall out in the open. (?)
Logged

Never change a password on a Friday                
SWMAN
Member

Posts: 543




Ignore
« Reply #5 on: April 29, 2011, 09:49:20 AM »

 Just curious; How do 300 foot tall cell towers,TV and commercial radio stations all stay on line during lightning storms ?
73 Jim. KF5HRN
Logged
KD5UDE
Member

Posts: 0




Ignore
« Reply #6 on: April 29, 2011, 10:00:07 AM »

yeah swman i like your question and even police fire and emergency managment dont unhook thier equipment so what do they do to stay hooked up? Huh
Logged
AA4PB
Member

Posts: 12644




Ignore
« Reply #7 on: April 29, 2011, 10:06:52 AM »

Just curious; How do 300 foot tall cell towers,TV and commercial radio stations all stay on line during lightning storms ?
73 Jim. KF5HRN

Properly installed antennas with properly installed grounding systems. This is often difficult (and expensive) to do in a typical home that has not been designed to accomodate a proper single point grounding system.
Logged
WB6BYU
Member

Posts: 12986




Ignore
« Reply #8 on: April 29, 2011, 10:08:10 AM »

Good grounding practices and surge suppressors.

The tower often extends above the antenna and takes the direct strike, rather than the antenna itself.  But such
antennas are often designed with a direct DC ground to dissipate any charge.  Everything has to be bonded to a
single common ground, especially at the bottom of the tower, so you don't get a voltage difference between, say,
your coax and your AC power wiring.  The coax surge suppressors should be mounted at that ground point before
going inside the equipment room in an attempt to keep all of the lightning current outside.

There is more to it than that, but overall it has to be done right and is not necessarily for the faint of heart.
I'm not an expert, but there have been many discussions in the forum over the years that will point you to
good references for how to do it.  I know W8JI says his towers get hit a couple times each year, with no
damage.  But you have to do it right at every point for it to work.
Logged
WA3SKN
Member

Posts: 5420




Ignore
« Reply #9 on: April 29, 2011, 12:43:53 PM »

Can it be done?  YES!  Take a look at commercial installations... low impedance conductors and good grounds work wonders.
Now, what is practical for YOUR installation?
Inside with an HT and a rubber duck antenna is not much of a target.  An inside small beam by the window is also fairly low key.  Outside antennas you will want grounded.  Many beams and J-poles can be installed this way.
They say that most installs below 60 feet do not increase your chances of being struck.
But...Just how good is your ground, anyway?  Is it bonded to your house ground?
And they now recommend using copper flashing as it has a very low impedance.  Do you have multiple rods in the ground?  It helps dissipate the power and heat of a strike.  And get any rod at least below the frost line.
Sounds like this spring is a good time to plan on some low cost improvements to the shack!
73s.

-Mike.
Logged
KE4JOY
Member

Posts: 1316




Ignore
« Reply #10 on: April 29, 2011, 02:25:38 PM »

The ground counterpoise rings around commercial towers are massive. They run huge bare braided copper conductors all around the base, they also drive 10'-0" long Cu clad ground rods 10' on center bonded to the counterpoise. The towers themselves bonded at 3 or more points with massive conductors tied to the counterpoise system. They also have massive very expensive 'cant fail' surge protection installed. You are talking 10's of thousands of dollars of 'systems' and that is just the grounding.

Even then occasionally they have failures. Most critical applications have redundant systems that can be brought on line quickly in case of such a failure.
Logged
AC5UP
Member

Posts: 3815




Ignore
« Reply #11 on: April 29, 2011, 02:59:27 PM »

Even then occasionally they have failures. Most critical applications have redundant systems that can be brought on line quickly in case of such a failure.

Thanks for saying that... From some of the comments above one might get the impression commercial sites never fail due to lightning but the fact is they do. Engineering goal is for the tower to be the absolute lowest impedance path to ground and take the hit instead of anything else. In practice Thor's hammer can do whatever Thor's hammer wants to do.

An install might survive 100 storms without so much as a hiccup but every new storm is a fresh roll of the dice. If you were paying attention to the weather this past week the storms that leveled parts of Arkansas, Alabama, Georgia, etc were all well beyond the norm and there are situations damned difficult to design for. On May 3, 1999 a string of tornadoes walked the Turner Turnpike from Midwest City through to Stroud, OK and if someone wanted to make the argument that God suffers from PMS that was one day when it would have made sense...  Shocked

http://www.nssl.noaa.gov/news/may3rd/outbreak.html

BTW: Has anyone noticed how well the weather radars tend to stay up during violent weather? I guess that's why you never see one near a mobile home park...............................
Logged

Never change a password on a Friday                
KE4JOY
Member

Posts: 1316




Ignore
« Reply #12 on: April 29, 2011, 05:09:45 PM »

BTW: Has anyone noticed how well the weather radars tend to stay up during violent weather?

Reminds me of the time my wife and I cowered in a dim hallway during Hurricane Andrew watching the weather on a battery TV. Being able to actually watch a storms progress via live radar was a novelty then. The radar station was actually only about 4 miles of our location. As the storm drew a bead on us we watched and prayed. The building, a 2 story CBS brick outhouse of a structure literally shuddered. The glass in the sliding glass doors bowed so far you could slide your hand in there.

We sat and watched the storm close.... fffftttt snow and no audio. I turned to my wife and said "They just lost the radar dish". Sure enough a few minutes later the TV station came on and explained that exactly that had happend. The storm had blew the radar dome off the top of the four story building and tossed it onto US1 like a beach ball.

My wife and I held each other and prayed as the shuddering got worse.


Sorry to stray off topic.
Logged
K9KJM
Member

Posts: 2416




Ignore
« Reply #13 on: April 29, 2011, 08:49:32 PM »

About the "Safest" way for a typical ham station to operate during a storm is to just use cross band repeat.
With a radio like the Kenwood TS 2000 (Itself properly protected with surge suppressors, Tower grounded, And all grounds bonded together)  And you do the actual talking with a small hand held radio (Acting as a wireless microphone)
(With the TS2000, This works for both VHF/UHF AND HF!)

As already pointed out, Commercial stations do NOT "disconnect" during storms.  (In fact to disconnect without properly grounding coax feedlines is DANGEROUS!) 
Logged
K0ZN
Member

Posts: 1525




Ignore
« Reply #14 on: April 29, 2011, 09:30:12 PM »


 A really EXCELLENT lightning ground system is expensive and labor consuming.....   Commercial level stuff is beyond the budget of most hams.
 A ham friend of mine works for a company that installs commercial systems and cell towers. Sometimes they go down over 120 ft. in our area to get the low resistance
ground they spec/demand.

Keep in mind you are trying to "guide" and "influence" millions of volts and MEGA watts of energy. It takes some LARGE conductors and a LOT of ground
contact. The good news is that there are a lot of ham towers and stations that are well done and able to survive multiple lightning hits without spending
thousands of dollars....but you won't do it for $20 either.

Based on what I have read in various books on lightning protection, my wild guess is that for good protection in average soil, one probably needs a rock bottom MINIMUM of about 8 (more is better) well spaced ground rods and quite a bit of AWG 2 or heavier cable. Again, we are trying to
find a "home" for THOUSANDS of AMPERES of energy and that takes some serious wire and ground.   
The corollary is: one or two rods is not really "protection", it is mostly a static electricity drain.
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!