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Is this story possibly true?


RF burn? Most likely not... If that was the case then walking past a local radio station should cook you alive!:lol: And 50k? what antenna handles that thats made for CB?


T23
 
He said the guy got burned on his wrist where he was wearing some jewelry. Maybe acting like an antenna???? His friend should be more careful of skin cancer and detached retinas with all that rf floating around.
 
He said he was wearing a gold bracelet , you do have a point about it acting as an antenna, but I think 50k is a bit far fetched, where would you get a linear to push that much wattage or even an antenna that could handle it?


T23
 
The story is interesting. Back 15 years ago there were guys who ran in the 50 KW range at the New Jersey keydowns. I remember the big Bird line sections and the meters were showing the claimed power. I was not completely convinced someone didn't tamper with the slugs until I saw one of the biggest corona arcs in my life. This guy keyed his mic and a corona arc ignited where the hardline connected to the base. It almost burned a hole through the sheet metal roof in about 3 seconds.

Of course you can't go to the Fat Boy website and buy this amp. Things in this power range are often one of a kind and custom built. There were also plenty of people walking around within 100 feet of the energized antennas and none complained about RF burns. The fact is you don't have to feel the RF burn for it to do damage! Some of the first signs of an RF overdose are headaches and blurry vision that can lead to blindness.

With respect to RF burns, you can jump on a AM radio tower pushing 50 KW without any ill effects so long as your feet are not on the ground when you make contact with the antenna. The frequency is lower so you are not at risk of blindness or headaches since the power passes through you. However, you can still get burned if you're grounded.

Knowing this makes me think it is unlikely this person got burned but still possible. Lets say it rained earlier that day and at some point this person stepped on something that put a pin hole in the bottom of his footwear. On his wrist we have a bracelet acting as an antenna and his foot is well grounded. All the bracelet needs to do is capture less then 1% of the radiated power to burn the man.
 
I was about to say that maby this guy was running a hombrew amp, but it seems like alot of trouble for a contest that pertains to just keying an showing meter results, if it were me it'd be a DX party, not a "lets keydown and look at some meters:laugh:"


T23
 
T23 said:
I was about to say that maby this guy was running a hombrew amp, but it seems like alot of trouble for a contest that pertains to just keying an showing meter results, if it were me it'd be a DX party, not a "lets keydown and look at some meters:laugh:"


T23
Click to expand...


It's not about looking at meters but rather talking over top of the guy parked next to you.

As for the RF burns, I find it hard to believe. I have worked around hot AM towers with up to 25 Kw and it was never an issue. Even standing in wet swampy ground at ten feet from the tower I never got a burn. Any closer and my skin started to crawl mind you but never a burn. Having said that I have seen loose barb wire fence connections arc and burn at 100 feet but the wire was acting as a HUGE antenna and coupling lots of RF to ground through a bad insulator.

When I had riggers on my FM tower I had to reduce power to about 25,000 watts ERP, down from 100,000 watts ERP for safety reasons.We had two stations on the site and the actual combined TX power for both frequencies was about 26,000 watts going into the antenna. That was too much RF in the immediate area for a person to be subjected too for reasons concerning the eyes and reproductive areas. :whistle: AFAIK the riggers never removed any rings etc before climbing and would hold a small fluorescent tube near each antenna bay to check for RF radiation.If they touched an antenna of course they would have gotten a very bad RF burn. Really, REALLY nasty actually. they did however report that there were times when their fingers would tingle from the RF.
 
I was wondering what country are these contests taking place, I mean this just seems like a mess for the FCC just waiting to happen...


T23
 
One thing about the AM tower is that the center of radiation is well above ground level and the longer wavelengths mean more metal is required to suck the RF in like that fence. I still don't find it likely that this person got an RF burn but I wouldn't take my shoes off having a bunch of metal on my body and stand parallel in front of an antenna energized with 50 KW.

Captain, just out of curiosity with the FM station. Did your high riggers pass by the FM bays when they were at 25 KW ERP? I always thought an FM station in this power range had to go off air or reduce power substantially in order to place personnel in direct proximity to the antenna bays.
 
Shockwave said:
One thing about the AM tower is that the center of radiation is well above ground level and the longer wavelengths mean more metal is required to suck the RF in like that fence. I still don't find it likely that this person got an RF burn but I wouldn't take my shoes off having a bunch of metal on my body and stand parallel in front of an antenna energized with 50 KW.
Click to expand...

It doesn't work quite like that.Any antenna radiates most of it's power where the current is the strongest. In the case of a loaded antenna, current is strongest in the loading coil and thus the center of radiation can be moved higher or lower by coil placement. In the case of a straight non-loaded 1/4 wave vertical,ie a typical AM radiator, the base of the antenna does most of the radiating. RF current is greatest at the bottom and lowest at the top. RF voltage is just the opposite,lowest at the bottom and highest at the top. The top of a 1/4 wave vertical does very little radiating. The bottom does most of it.

Captain, just out of curiosity with the FM station. Did your high riggers pass by the FM bays when they were at 25 KW ERP? I always thought an FM station in this power range had to go off air or reduce power substantially in order to place personnel in direct proximity to the antenna bays.
Click to expand...


Forgot to mention that the power was indeed switched OFF when the riggers were within the antenna bays. The 25 Kw limit was only when they were working somewhat below the lowest bay or on an adjacent tower when removing it. This is because the antenna we were using was a 12 panel/4 bay antenna that had four antenna panels on each of the three tower faces making it impossible to climb above the lowest antenna panel without physically contacting the antenna itself.
 
I completely agree with the current distribution on the 1/4 wave AM tower as you describe. My point is that the frequencies used on AM present a much different RF exposure level on the ground with the 200 foot 1/4 wave. On 11 meters you have the entire 1/4 wave mobile antenna radiating it's full energy at near ground level. On the AM tower this base current is spread out over a much larger area then where your body would be on the ground. This is why a high power FM station must get it's center of radiation well above ground level to meet RF exposure safety levels. Height at higher frequencies is not just about coverage, it deals with RF levels on the ground too.
 
Shockwave said:
I completely agree with the current distribution on the 1/4 wave AM tower as you describe. My point is that the frequencies used on AM present a much different RF exposure level on the ground with the 200 foot 1/4 wave. On 11 meters you have the entire 1/4 wave mobile antenna radiating it's full energy at near ground level. On the AM tower this base current is spread out over a much larger area then where your body would be on the ground. This is why a high power FM station must get it's center of radiation well above ground level to meet RF exposure safety levels. Height at higher frequencies is not just about coverage, it deals with RF levels on the ground too.
Click to expand...


Well sorta, kinda, maybe. ;) The primary reason for elevating the antennas is coverage. You can do a lot more with a measly 500 watts at 300 feet than you can at 50 feet and still be within exposure limits at either height.

Not sure about in the USA but we have three different standards of RF exposure limits here. One is for the general public that have no control over how much RF they receive, another is for the general public that do have control such as walking in a field containing an AM transmitter or hiking to the base of an FM tower, and a third for RF workers who have complete control and are able to limit exposure.By law signs must be posted at the borders of these limits warning of RF exposure and indicating that only RF workers are permitted beyond a certain area. Riggers on the tower are exposed to thousands of times as much RF as the general public are.Even we lowly station engineers that don't climb are subjected to huge amounts of RF while in the transmitter house compared to the limits granted to the general public. That is where the time factor in exposure limits kicks in.
 
Are you ready?

Once upon a time I happened to be in a 'tour' group through a hydroelectric generating plant. Part of that tour was walking past one of the generators. That thing was about the size of a very 'pregnant' 15 - 20 foot 'Airstream' trailer. We were warned about wearing metal, having metal dental fillings, sutures, etc. We were told that at any sign of discomfort to not approach any closer to that generator. The areas around that generator were marked in various ways according to the severity of exposure too. There was absolutely no doubt when you got 'close enough'. I have no idea of the amount of current being produced by that generator, but would feel safe in saying it was more than you'd be exposed to near a 50Kw CB radio/amplifier. Those warning areas were in '10's of feet, not '100's of feet, and none of us were allowed to 'cheat' on how close we got, even if we had wanted to. I had dental fillings. I didn't want to do any of that 'cheating'. Ever have a filling and drink very cold water and regret it? I think you can get an idea from that.
If there was someone who was burned from RF exposure at 100 feet from that transmitter/antenna, and there -weren't- others closer screaming, I'd have to tend to believe that 'all' of the story isn't being told.
- 'Doc
 

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