Can FM transmitters burn humans?

[AnyHuman]

Can the exiting power from, say, a 100,000 watt FM station burn a human if they're working at a site with the antenna on?

If so, how do the engineers who set those things up work, do they have protection of some kind if they need to go in to fix something?

Just a curious question from a technical-minded human, I've never worked at a radio station and have little knowledge of the operation of transmitters.

 

[davideduardo]

Can the exiting power from, say, a 100,000 watt FM station burn a human if they're working at a site with the antenna on?

If so, how do the engineers who set those things up work, do they have protection of some kind if they need to go in to fix something?

Just a curious question from a technical-minded human, I've never worked at a radio station and have little knowledge of the operation of transmitters.

If a person is actually touching an AM or FM antenna, they can be electrocuted or get bad RF burns.

OSHA has determined that there is a level of FM radiation that is not permitted at ground level. So stations control the radiation off the antenna in a downward angle at the tower base and immediate vicinity. OSHA rules will not allow a certain level of radiation on a tower if there is work being performed on it. The rules are specific to frequency range.

More dangerous are microwaves. An engineer I worked with many years ago was working in front of a TV microwave antenna while the transmitter was purposely turned off. Some moron turned it on. He felt it after a few minutes and went to the hospital where he vomited, pissed blood and was under medication for over a week. He eventually died of cancer of the stomach, likely related.

Remember, the whole tower is the antenna for AM. For FM, just the bays are the antenna and the tower is just there to hold the bays up in the air.

 

[AnyHuman]

So you won't get burned if you're, say, at a transmitter shack just hanging around messing with controls on the processor or turning on/off the transmitter? You're not touching the antenna itself in such a situation, you'd be just touching controls.

 

[davideduardo]

So you won't get burned if you're, say, at a transmitter shack just hanging around messing with controls on the processor or turning on/off the transmitter? You're not touching the antenna itself in such a situation, you'd be just touching controls.

No. If the installation was done to code, there is nothing dangerous. Inside most of the transmitter, the danger is from electricity, not RF. Generally, the radio frequency energy.. the signal... comes out of a shielded part of the transmitter directly into the transmission line. A line is a copper or copper braid tube with dielectric (dry air or gas) and a center conductor that carries the signal to the antenna elements.

Like any electrical installation... such as the electrical room in an office building or apartment building... it is good to know what you are doing or you can damage the equipment by mis-adjusting it.

Many stations that have the transmitter at the studio location will have the audio chain in a cabinet with a locked door to keep people from messing with the settings.

KRTH in LA used to have a smoked glass door on the processing, so nobody could see what equipment was in there and what the settings were!

 

[AnyHuman]

Nice. I'd hate to get burned on an antenna TBH if I had to get it going again after an equipment failure.
I understand about stations wanting to protect their nice audio settings so nobody else could steal and use them. But I'd personally show off my nice expensive gear to listeners, or at least have a photo of the gear in plain view in public if I owned a station, to be educational about it.



BTW I'm scared of what happened to your poor engineering co-worker. Hopefully nobody does that again turning on equipment without reason.

 

[davideduardo]

Nice. I'd hate to get burned on an antenna TBH if I had to get it going again after an equipment failure.
I understand about stations wanting to protect their nice audio settings so nobody else could steal and use them. But I'd personally show off my nice expensive gear to listeners, or at least have a photo of the gear in plain view in public if I owned a station, to be educational about it.

At one station I managed, we had all the equipment in front of a glass wall that listeners who came for prizes could see from the lobby. We added a bunch of panels we made that had lights that moved with the music, of blinked or changed color. They otherwise did nothing. But they looked very cool. Listeners seemed fascinated about "how complex" it all was. That made the visit thrilling for them.

For a while, we did Polaroid pics (long before selfies) of listeners in front of the equipment and our logo. We heard that some people had them in their kitchen for 5 or 6 years or more. It's show business.

 

[Kelly A]

A long time ago I was working as Chief for a 5KW ND Day AM station with a Truscon 570' self supporting day tower. Just so happened I was at the transmitter site finishing up some last minute things before heading home when the station bumped off the air for a second, then again.

Come to find out two high school age boys were trying to climb the tower. One of them managed to crawl over one the the 5' tall base insulators, suffering some significant RF burns to his hands, knees, and soles of his feet. Once above the insulator, he clung to the tower leg with his arms death gripping the leg wailing like a baby. His buddy got one hand above the insulator, got zapped, and fell off the 8' tower leg plinth to the ground. Other than the burn to his hand, some bumps and bruises, he fared better than his pal that somehow made it over the insulator. Good thing it wasn't a 50kw site. The one who made it over the insulator probably would have lost some fingers, if not his whole hand.

 

[kf4rca]

I've heard from tower climbers that you can climb up on a low band VHF TV antenna (super turnstile type) while it is on the air safely. The power density is low due to the long wavelength. (The wavelength of Ch.2 is approximately 18 feet.) But of course , there are no more of these on the air these days.
AM's are safe to climb if you get on with a fiberglass ladder. Once on, you cannot touch any conduits, running thru the center, for lighting, etc. that might be grounded.

 

[awsherrill]

AM's are safe to climb if you get on with a fiberglass ladder. Once on, you cannot touch any conduits, running thru the center, for lighting, etc. that might be grounded.

Not always the case. On AM towers that have lighting installed, the conduit is usually at tower potential and it is safe for a climber (on the tower) to touch. Lighting chokes or ring transformers are used to get the AC power for the lights across the insulated tower base.

Some base-insulated AM towers do have transmission lines running up to a bonding connection at the quarter-wave point on the tower, with insulators separating them from the tower. Those would not be safe for a climber to touch. Also some AM towers have sample loops that may be at ground potential, and climbers would need to avoid coming in contact with them.

I have not seen any small cross-section AM towers that had insulated lines or conduits running up the middle of the tower (doesn't mean they don't exist). One of our AM stations has a huge Blaw-Knox self-supporting tower that has transmission lines running up the middle. The lines are bonded at the quarter-wave point and are supported by insulated cables strung inside the tower steel.

Back to the OP's original question, if everything is working right in the transmitter building, there is little or no physical danger to people working in there. If things get sideways, people can get hurt. I have seen transmission line sections inside a transmitter shack get extremely hot when a "bullet" goes bad in a flange connector. That wouldn't be an RF burn if you touched it, but it would hurt every bit as badly.

 

[RadioFan2J3]

AM's are safe to climb if you get on with a fiberglass ladder. Once on, you cannot touch any conduits, running thru the center, for lighting, etc. that might be grounded.

One big issue with climbing a hot painted AM tower is RF burns, depending, of course, on the power level, especially if the climber does not use gloves.

The paint on the tower may be an insulating layer and RF will find holes in the paint and that may startle the climber, at the very least.

 

[WPPCProductions]

Interesting topic..Safety first as always.

As before they would say .Mom will say"Dont sit too close to a CRT type TV set" and now they say 5G will fry peoples brains...

 

[kf4rca]

I once knew a guy who did sat truck uplinking (Ku band) for 10+ years for a major market TV station. Really nice guy. The sat truck also had 2G microwave for local shots. He really was more of an operator than an engineer. Didn't have a first phone but had a degree in computer science.
Anyway he decides to get married to a gal he met at church. She gets pregnant and the child is born with spina bifida.
Coincidence? Maybe. Maybe not.
Sad story.

 

[Kelly A]

One big issue with climbing a hot painted AM tower is RF burns, depending, of course, on the power level, especially if the climber does not use gloves.

The paint on the tower may be an insulating layer and RF will find holes in the paint and that may startle the climber, at the very least.

Once you get above the base insulator, you can climb without any risk. Painted or not. The issue for AM towers is when you become a conductor to ground across the insulator.

 

[kf4rca]

Now, you can't climb a UHF (pylon) antenna or a VHF hi-band antenna with or without gloves. Lots of those antennas still in service.
Also you can't climb above the platform on a candlabra mount antenna, with or without gloves. Many candlabras still around.
I've heard its safe to work on the rear side of a CBR antenna. A CBR (cavity backed radiator) is a circular polarized antenna for TV broadcast. Some of those are still around in hi-band VHF service.
I've heard its unsafe to climb a tower thru the area with several hi power FM arrays side mounted to the tower.

 

[gr8oldies]

I managed to get RF burns from my ham rig once.

 

[RadioFan2J3]

Once you get above the base insulator, you can climb without any risk. Painted or not. The issue for AM towers is when you become a conductor to ground across the insulator.

I agree with you regarding the issues of crossing the base insulator.

In regards to RF burns once on the tower, I will disagree with you. I can assure you that the first time I climbed a hot tower, 5kW, far too many years ago, and climbing without gloves, I'd get minor RF burns on my hand, minor arcing between the tower steel and my hand, when the insulating factor of the paint was insufficient. The first few times it happened on that climb, I was a bit startled, but once I realized what was happening, I tried to be far more careful.

I will agree with you, none of this was anything close to what I might have experienced had I tried to cross the base insulator and touched the ground and the tower at the same time.


Adding, the RF burns while climbing were far more a nuisance than risk to life, other than perhaps reacting to the small arc and letting go of tower steel. That is why I mentioned being startled by the RF burn from the RF arc.

 

[davideduardo]

Once you get above the base insulator, you can climb without any risk. Painted or not. The issue for AM towers is when you become a conductor to ground across the insulator.

Anecdote time:

When at WEEL in Fairfax, VA, in 1969 we had a jock who always made a Friday date via the request line (a whole subject itself). Prior to leaving the station after his PM drive shift, he'd go out to the hottest of the four towers and jump onto it. He would hang onto the bottom section for about ten minutes and then he would jump back off, confident that all his little swimmers had been blasted out of existence by the RF and that using an umbrella was not necessary.

 

[Oldie919]

Anecdote time:

When at WEEL in Fairfax, VA, in 1969 we had a jock who always made a Friday date via the request line (a whole subject itself). Prior to leaving the station after his PM drive shift, he'd go out to the hottest of the four towers and jump onto it. He would hang onto the bottom section for about ten minutes and then he would jump back off, confident that all his little swimmers had been blasted out of existence by the RF and that using an umbrella was not necessary.

For added "safety".......he could have checked himself with a spectrum analyzer for any "spurious emissions"......!

 

[kf4rca]

I've heard that the some tower climbers put tin foil around their 'nads for protection from birth defects. Must be awfully uncomfortable.

 

[awsherrill]

I've heard that the some tower climbers put tin foil around their 'nads for protection from birth defects. Must be awfully uncomfortable.

Apparently not just tower climbers...

https://www.thebdr.net/articles/warstories/worst/Worst-RFR.pdf

"RF suits" do exist. They are used by tower crews when working around antennas that absolutely, positively have to keep radiating. Much more effective than tin foil, although I have heard that they can be uncomfortable in warm weather.