-
Get involved.
We want your input!
Apply for Membership and join the conversations about everything related to broadcasting.
After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
If you use a disposable or false email address, your registration will be rejected.
After your membership is approved, please take a minute to tell us a little bit about yourself.
https://www.radiodiscussions.com/forums/introduce-yourself.1088/
Thanks in advance and have fun!
RadioDiscussions Administrators
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
when lightning strikes a tower..
- Thread starter Shredder
- Start date
The towers next to the WDHA studios are actually WMTR's. WDHA's is several miles away.
If you were listening to WMTR at that moment, you might hear a brief drop of the signal, as the transmitter reacts to the lightning strike by enacting a "VSWR Overload", which briefly (less than a second typically) removes power to the antenna to prevent circuit damage.
Since lightning hits those towers periodically and the system is well grounded, the people inside probably only noticed the thunder.
If you were listening to WMTR at that moment, you might hear a brief drop of the signal, as the transmitter reacts to the lightning strike by enacting a "VSWR Overload", which briefly (less than a second typically) removes power to the antenna to prevent circuit damage.
Since lightning hits those towers periodically and the system is well grounded, the people inside probably only noticed the thunder.
I don't know if that is entirely true. We have our tower extremely well grounded and still have had equipment zapped. We add more and more layers of protection but it seems that if you get the right hit, electronic equipment can take a fall.
I honestly don't think there is a protection that can offer 100% guarantee you won't lose equipment.
I honestly don't think there is a protection that can offer 100% guarantee you won't lose equipment.
Here's a good example of what happens when lightning hits a radio station's tower
and studio...Happened here in South Carolina back on June 4th...really bad for them.
http://radiodiscussions.com/smf/index.php?topic=235546.0
and studio...Happened here in South Carolina back on June 4th...really bad for them.
http://radiodiscussions.com/smf/index.php?topic=235546.0
josh said:We have our tower extremely well grounded and still have had equipment zapped.
My guess is that the nature of how the antennas work and how we feed them, the old traditional A.M. station can take lightning strikes in stride and shrug them off in many cases, but the F.M. stations are very likely to suffer severe lightning damage. In an A.M. station the feed-line stops at the dog-house at the bottom of the tower and if the "network" of components to transition the power from the feed line to the tower are carefully laid out, there is seldom reason for the major impact of a lightning strike to travel through the feed line to the transmitter. (I've been in the transmitter room or on the other side of the glass when lightning has displayed itself dancing around the coffee-pot sized tubes and it can indeed be an awesome display!!!!)
But in FM, the transmission line goes all the way up the tower to the antenna and is something of a continuous conductor all the way to the transmitter. It serves as a super Highway for lightning surges. And we will have to let the folks who maintain these transmitters on a daily basis speak to this issue, but my guess is that when we went from tube-type transmitters to solid-state transmitters, it totally changed the vulnerability to lighting, and what techniques are needed to prevent and minimize lightning damage.
"Positive Lighting"..a 'bolt from the blue". I had several of them from from Sister Angela's yardstick on the back of the head at St. Aloysius!
Never in real life though. At WMID/WGRF, we had several strikes while I was there in the building, and usually all that would happen is, as MikeF said, the FM would shut down for safety. I'd go back, the filaments would be on, but the VSWR had tripped, and no B+. Just reset and on the air. The AM would pop to "nightime" mode, 250 watts. Just switch back to 1kw if daytime. No burned equipment, just frayed nerves of staff.
That building is strapped under the floors from back at the tower doghouse to the front door sidewalk with copper, and the studios are lined/encased in it, all welded to that strap. Then all grounded to earth.
Never in real life though. At WMID/WGRF, we had several strikes while I was there in the building, and usually all that would happen is, as MikeF said, the FM would shut down for safety. I'd go back, the filaments would be on, but the VSWR had tripped, and no B+. Just reset and on the air. The AM would pop to "nightime" mode, 250 watts. Just switch back to 1kw if daytime. No burned equipment, just frayed nerves of staff.
That building is strapped under the floors from back at the tower doghouse to the front door sidewalk with copper, and the studios are lined/encased in it, all welded to that strap. Then all grounded to earth.
Here in Dallas at the Cedar Hill tower "farm" there are 11 plus towers over 1500 feet tall. They always take hits during storms. At most as Goat Rodeo Cowboy said, you will get a VSWR "overload" and that's about it whether the transmitter is tube or solid state. I've ran both. Continental combined tube type (816R series) and Nautel solid state (NV-40).
I do slightly disagree with Goat Rodeo Cowboy on the vulnerability of the FM and TV transmitter towers over AM transmitter towers since the AM feedline does run from the transmitter output though the phaser (if used) all the way out to the matching network at the tower...these days typically an unbalanced or coaxial type feedline. The coax/feedline is grounded at the network in the tuning house, with the "hot" side attached to the tower. With the tuning network grounded at the tower, the lightning "usually" stops there unless the ground is compromised...
From my experience FM/TV towers are in general less susceptible to strike damage since the transmission feedline is bonded every 50 feet or so, down the entire length of the tower. In times past when some of my sites used individual rather than master antenna systems, we would take a strike which would damage a bay. But that was a rare occasion since the mass of the support structure (the tower) usually attracted the strike.
On some FM/TV towers you will see lightning and corona discharge devices which resemble metallic whisk brooms mounted above the the top of the tower to direct the strike to the mass of the tower. AM towers, unless they are shunt fed, are mounted on a base insulator and rely on the "johnny balls" (spark gap) at the base to "arc over" to protect the tuning network, the phaser and transmitter. This spark gap is set so it is wide enough not to flash over on modulation peaks, when the RF P.E.P. is at maximum, and yet set close enough to provide the lightning strike a low resistive path to ground at the base of the tower..yet another reason for the multiple 4 inch copper ground straps from the base insulator to the ground radials...
There are no "Sure Bet" ways to protect from a hardcore lightning strike. If the strike can pass though 6 miles of AIR, there's not much in the way of a man made insulator that can stop one. At best you strive to create the least resistive path to ground, without having equipment in that path...
Usually when that path fails on an AM tower it's because of contamination (bird crap) on or mis-adjustment of the spark gap (gap to wide) which allows the lightning into the tuning house and points closer to the transmitter. In the early days of solid state AM when MOSFETS and power combiners were not as "robust" some stations would fire up the trusty GATES BC1xx and run it until the storm passed. Today's solid state AM transmitters DX-50, DX-10, etc are much more "forgiving"...
I do slightly disagree with Goat Rodeo Cowboy on the vulnerability of the FM and TV transmitter towers over AM transmitter towers since the AM feedline does run from the transmitter output though the phaser (if used) all the way out to the matching network at the tower...these days typically an unbalanced or coaxial type feedline. The coax/feedline is grounded at the network in the tuning house, with the "hot" side attached to the tower. With the tuning network grounded at the tower, the lightning "usually" stops there unless the ground is compromised...
From my experience FM/TV towers are in general less susceptible to strike damage since the transmission feedline is bonded every 50 feet or so, down the entire length of the tower. In times past when some of my sites used individual rather than master antenna systems, we would take a strike which would damage a bay. But that was a rare occasion since the mass of the support structure (the tower) usually attracted the strike.
On some FM/TV towers you will see lightning and corona discharge devices which resemble metallic whisk brooms mounted above the the top of the tower to direct the strike to the mass of the tower. AM towers, unless they are shunt fed, are mounted on a base insulator and rely on the "johnny balls" (spark gap) at the base to "arc over" to protect the tuning network, the phaser and transmitter. This spark gap is set so it is wide enough not to flash over on modulation peaks, when the RF P.E.P. is at maximum, and yet set close enough to provide the lightning strike a low resistive path to ground at the base of the tower..yet another reason for the multiple 4 inch copper ground straps from the base insulator to the ground radials...
There are no "Sure Bet" ways to protect from a hardcore lightning strike. If the strike can pass though 6 miles of AIR, there's not much in the way of a man made insulator that can stop one. At best you strive to create the least resistive path to ground, without having equipment in that path...
Usually when that path fails on an AM tower it's because of contamination (bird crap) on or mis-adjustment of the spark gap (gap to wide) which allows the lightning into the tuning house and points closer to the transmitter. In the early days of solid state AM when MOSFETS and power combiners were not as "robust" some stations would fire up the trusty GATES BC1xx and run it until the storm passed. Today's solid state AM transmitters DX-50, DX-10, etc are much more "forgiving"...
In 1984, I was on the air on a Sunday afternoon at WCVC-AM in Tallahassee, Fla., when a severe t-storm approched. The 231foot tower was out behind the studio mobile home.
When the lightning hit the tower, it shattered the red beacon. The station was knocked off the air, and was off the air for a couple of days as they had to order some parts for the Harris MW-5.
The exact scenario repeated itself exactly two weeks later, also with me on the air on Sunday afternoon.
From my point of view it was a little un-nerving, being the only one there when it happened.
They wised up and installed some lightning protection and additional grounding after that.
When the lightning hit the tower, it shattered the red beacon. The station was knocked off the air, and was off the air for a couple of days as they had to order some parts for the Harris MW-5.
The exact scenario repeated itself exactly two weeks later, also with me on the air on Sunday afternoon.
From my point of view it was a little un-nerving, being the only one there when it happened.
They wised up and installed some lightning protection and additional grounding after that.
- Status
- This thread has been closed due to inactivity. You can create a new thread to discuss this topic.