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rf burn
If I touch the coil in my tuner while transmitting I get a painful rf burn.
But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? |
rf burn
If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? although an over-simplification, the bird is not touching anything else, (grounded)... but you are. |
rf burn
even if you aren't touching something you have a much larger surface area to
act as a capacitive path to ground for the rf. the small bird being a long distance from ground and having a smaller area has much smaller capacitive currents. "Ed" wrote in message . 192.196... If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? although an over-simplification, the bird is not touching anything else, (grounded)... but you are. |
rf burn
Frank Alforo wrote:
If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? You could probably hang by one hand from a 20 kV power line and be OK as long as you didn't complete a current path to another wire or ground. -- 73, Cecil http://www.qsl.net/w5dxp |
rf burn
Hi Frank
Although ot answering your question I thought I might relate a recent experience of my own. I remember various RF burns over the years. I never however thought I would have an issue with a 18dBm (100mW) 11GHz TX I work on in my employment. The fault was low output and I was doing an initial feel around with my fingertips, not actually touching an active citcuit metal but looking for excess heat. I then rested my finger on a small screwhead (maybe M2.5) that held the PCB down neear the output stripline (after the MMIC) and got enough of a burn that it felt like a static discharge spike one gets from a nylon carpet. It was a whoppa and totally unexpected! I never did try to reason why the burn happened. The screw was loose about 2-3 turns so I am thinking a tuned cct of some kind with my finger as part of the dielectric! Oh an tighting the screw solved the low power problem! Cheers Bob VK2YQA Frank Alforo wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? |
rf burn
Two major things involved:
1. Depends where you (bird) is touching, you are prone to get more pronounced burn at the high voltage part of circuit (coil, antenna). Higher impedance point - higher voltage - easier, more burn or draw the arc. We used to light up cigarettes by keying the transmitter, touching with pencil the "hot" end of the tank coil and drawing the arc, while puffing. W8JI might argue that current/voltage is ALWAYS THE SAME along the coil, so stand by for more scientwific 'splanation :-) Anyone trying above experiment can easily see that it is easier to draw the arc at high voltage (low current) end of coil than vice versa. 2. Depends on the area/mass (capacitance) of what is touching the RF hot part of the circuit. Fat person vs. small bird would make a big difference. If one end of the person is (capacitively) grounded, the more pronounced effect. 73 -- Yuri Blanarovich, K3BU, VE3BMV "Frank Alforo" wrote in message ... If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? |
rf burn
Your impedance is lower...
On Sat, 24 Jun 2006 21:59:11 -0700, "Frank Alforo" wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? John Ferrell W8CCW |
rf burn
"Cecil Moore" wrote in message
.com... Frank Alforo wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? You could probably hang by one hand from a 20 kV power line and be OK as long as you didn't complete a current path to another wire or ground. -- 73, Cecil http://www.qsl.net/w5dxp Beware of the gradient! |
rf burn
"Cecil Moore" wrote in message .com... Frank Alforo wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? You could probably hang by one hand from a 20 kV power line and be OK as long as you didn't complete a current path to another wire or ground. -- 73, Cecil http://www.qsl.net/w5dxp You should have seen the TV educational channel where in some countries they have a basket type trolley that men are put in and hung by helicopter on the multi megavolt lines. They do wear some kind of suit that is conductive so the charge will not affect their body so much. |
rf burn
"Ralph Mowery" wrote in message
. net... You should have seen the TV educational channel where in some countries they have a basket type trolley that men are put in and hung by helicopter on the multi megavolt lines. They do wear some kind of suit that is conductive so the charge will not affect their body so much. You mean these guys? http://www.haverfield.com/ -- Gerry |
rf burn
It's the current which matters.
The bird has a capacitance to the rest of the world which depends on its size. The current which flows up the bird's legs is the voltage on the antenna divided by the capacitive reactance of the bird's body. For small birds the capacitance is only a few picofarads and so the current is extremely small. The bird continues to sing its happy song. Whereas, a human body not only has a much larger capacitance it may also complete the circuit by having the other hand in contact with grounded metal work. Or the victim might be standing in his bare feet. The current due to capacitance of the human body alone is enough to cause burns. The pain is sufficient to stop the human from singing and begin using bad language. ---- Reg. |
rf burn
Reg Edwards wrote:
It's the current which matters. The bird has a capacitance to the rest of the world which depends on its size. The current which flows up the bird's legs is the voltage on the antenna divided by the capacitive reactance of the bird's body. For small birds the capacitance is only a few picofarads and so the current is extremely small. The bird continues to sing its happy song. I did surprise an Owl one night sitting astride my Inv-V center insulator. He was apparently touching both dipole wires when I went key down with 100 watts. -- 73, Cecil http://www.qsl.net/w5dxp |
rf burn
Ralph Mowery wrote:
"Cecil Moore" wrote in message .com... Frank Alforo wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? You could probably hang by one hand from a 20 kV power line and be OK as long as you didn't complete a current path to another wire or ground. -- 73, Cecil http://www.qsl.net/w5dxp You should have seen the TV educational channel where in some countries they have a basket type trolley that men are put in and hung by helicopter on the multi megavolt lines. They do wear some kind of suit that is conductive so the charge will not affect their body so much. They ;do that in this country. Mesh suit of some metal, can't remember which metal but not important as long as it's conductive I guess. Great job I bet, big bucks.... |
rf burn
"Dave" wrote in message . .. even if you aren't touching something you have a much larger surface area to act as a capacitive path to ground for the rf. snip Yes. One of the standard tools used during RADHAZ inspectiions at RF transmitters sites is an RF Burn Gun. (It's shaped like a gun for convenience of holding and use.) It measures the RF potential on metallic structures near a transmit antenna and the tech is part of the circuit, coupling to ground. Current limiting in the RF Burn Gun keeps the tech from harm while he reads the potential off a meter in the "gun." It strikes me that the measurement accuracy varies with operating frequency and size of the tech (via collective X-sub-C). With my big butt and short legs, I might offer more coupling to ground than you scrawny people. |
rf burn
There's a great difference between working on antenna conductors and
60 Hz power lines. Body capacitance is all-important at HF. At 60 Hz it is the conduction path which matters. Workmen can be enclosed in Faraday screens. |
rf burn
Frank Alforo wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? What Muppet Labs would like to know is why you touch the coil in your tuner while you are transmitting. Don't do that! Also avoid things like putting your fingers across live mains conductors and placing your hand on hot stoves. Bunsen |
rf burn
Frank Alforo wrote:
"But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world." Frank isn`t using enough power. I worked in a shortwave broadcasting plant filled with 50 KW and 100 KW DSB fully modulated transmitters. Our relatively flat transmission lines were of the 2-wire unshielded 600-ohm variety. These lines must have attracted countless tired migratory birds to alight or try to alight. When a bird would try to grasp a wire, it would instantly be consumed in a puff of smoke and steam. No carcass fell to the earth. Poof! it was gone. Many times their claws were left behind gripping the wire leaving us a record of the bird`s visit. Many wires were covered with bird claws. RF can kill more birds than cats can. Best regards, Richard Harrison, KB5WZI |
rf burn
On 2006-06-26, Richard Harrison wrote:
bird`s visit. Many wires were covered with bird claws. RF can kill more birds than cats can. Maybe we can use this to distract people who claim wind farms are bird killers. -- Ben Jackson http://www.ben.com/ |
rf burn
Okay silly question Richard
Did the birdless claws have any noticable effect on the match/tuning of the antenna? grin Cheers Bob Richard Harrison wrote: steam. No carcass fell to the earth. Poof! it was gone. Many times their claws were left behind gripping the wire leaving us a record of the bird`s visit. Many wires were covered with bird claws. RF can kill more birds than cats can. |
rf burn
"Frank Alforo" wrote in
: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? The bird is (usually) small compared to the wavelength. Much smaller than you are. And, except at the ends of antenna elements, the voltage is not particularly high. Whereas there is a high voltage across your coil and you are a much larger portion of a wavelength than the bird, so significant current will flow into you if you touch the coil. -- Dave Oldridge+ ICQ 1800667 |
rf burn
On Sun, 25 Jun 2006 12:09:18 GMT, Cecil Moore
wrote: Frank Alforo wrote: If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? You could probably hang by one hand from a 20 kV power line and be OK as long as you didn't complete a current path to another wire or ground. You could probably hang by both hands if they were close together. I would not want to try it, though. When I worked in broadcast radio years ago, I was always amazed that service personnal would climb the 10 kw tower hot to change lights. They stated they could feel potential between their hands as they climbed. Win, wolz |
rf burn
"Win" wrote
You could probably hang by one hand from a 20 kV power line and be OK as long as you didn't complete a current path to another wire or ground. You could probably hang by both hands if they were close together. I would not want to try it, though. When I worked in broadcast radio years ago, I was always amazed that service personnal would climb the 10 kw tower hot to change lights. They stated they could feel potential between their hands as they climbed. _____________ But the a-c frequency is important here. The voltage gradient between adjacent hand grips for power in a conductor at AM broadcast station frequencies (the vertical antenna radiator, in this case) is a lot higher for the same conducted power than for that same span along a conductor on the 50/60 Hz a-c power grid. RF |
rf burn
Frank Alforo wrote:
If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? Frank, Some basics. There are two types of RF radiation, Non-ionisation and Ionisation radiation. The HF bands are non-ionisation ( normally ) and the damage you'll notice is generated either from High Voltage or RF Radiation. Look in the ARRL handbook on RF safety. Different parts of the body have different frequency ranges where we have extra absorption of RF radiation. Touching a coil in the tuner? This type of RF burns are either primary High Voltage or secondary = induced or transferred via capacitance to a metallic object within the antennas RF field. ( Why the F**K do you touch a coil in tour tuner whilst transmitting!? ) Do you put your finger in your cars cooling fan too? The result is tingling sensations and direct proportional of the power ( or stupidity ), different Voltages will occur. High Q antennas can have really nasty voltages, like magnetic loops. High Voltage gives burns and can give nasty and very deep internal damages. Read your safety regs! You are supposed to know these regs as a ham!!! Radiated RF. Non-ionising RF radiation can be compared to sunlight. To much RF radiation and your body ( or parts ) will heat up. The effects are like sunstroke or prolonged exposure to hot climate. Short term effects are nausea and fainting - like a sunstroke! A small bird will have problem with RF Radiation but less problem with High Voltage. unless both poles are present and the stupid bird touches both. Birds ( as in flying small animals ) have often none or minor problems as a difference from the other type of birds, that develops to YL's and XYL's... ( No, you are not allowed culling XYL's with RF radiation! ) Ionising radiation is a different matter and is what we normally call "radioactive radiation". The energy levels of this type of radiation is much(!) higher than normal RF radiation and if you don't know you are near areas with this type of radiation, you are either trespassing or plain stupid.... Generally, higher frequencies, especially in the microwave spectra, tend to contain high energy levels. Also, bear in mind that the frequency where water absorbs RF radiation is around 2.4GHz. If you are inside a high intensity field, get out! One of the first things to be damaged in a high RF intensity RF field is your eyes. They might coagulate and I promise - that's a bad thing and most probably irreversible. The good thing is tho' - you don't need glasses anymore... Another thing not to do is to place your glutus maximus over a wave tube with power on --- ********! Now then.... Most accidents where RF burns and RF radiation exposure occures, creates damages from a fall, not by the RF radaition itself! People tend to climb up on ladders and on masts before they decide to get zapped... Bad idea as most of them fall down and break arms and legs at the best... ///// No, I'm not a safety freak but I have a valid certificate for work in masts and on rooftops where there are aerials... Cheers All Dan / M0DFI |
rf burn
Dan Andersson wrote: ( Why the F**K do you touch a coil in tour tuner whilst transmitting!? ) Do you put your finger in your cars cooling fan too? I reached over to adjust the capacitor not realizing that the set screw that fixes the capacitor knob onto the capacitor shaft stuck up beyond the surface of the knob shaft. My finger reached over and touched the end of the screw as I keyed down. My free hand was not grabbing a ground wire. I was sitting in an upholstered chair which was on a rug which was on a wood floor. And no, I do not put my finger in my car's cooling fan. Frank A. |
rf burn
In article , Win
wrote: When I worked in broadcast radio years ago, I was always amazed that service personnal would climb the 10 kw tower hot to change lights. They stated they could feel potential between their hands as they climbed. Win, wolz Hello, and was that a shunt-fed AM broadcast tower? You might just get away with a grab at ground level. OTOH, I would think that grabbing onto a live base-insulated type tower would have serious consequences when being fed by a 10 kW transmitter. Just looking at the RF bypass hardware needed at the base to provide for tower lighting (Austin transformer or Collins lighting choke) should be enough to say "keep away" while transmitting. Sincerely, and 73s from N4GG0, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
rf burn
"Frank Alforo" wrote in message
... If I touch the coil in my tuner while transmitting I get a painful rf burn. But a bird can perch on my antenna wire while I transmit 100 watts and it stays there seemingly without a care in the world. How come? Because the bird is smarter? west |
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