rf burn
Frank Alforo
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?
Ed
although an over-simplification, the bird is not touching anything
else, (grounded)... but you are.
Dave
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" <Huckleber...@bigvalley.net> wrote in message
news:Xns97ECE3DB4AB78sp...@198.186.192.196...
Cecil Moore
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
Yuri Blanarovich
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" <fal...@dslextreme.com> wrote in message
news:129s61p...@corp.supernews.com...
Bob Bob
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
John Ferrell
John Ferrell W8CCW
Philo
news:O1vng.123149$dW3....@newssvr21.news.prodigy.com...
Beware of the gradient!
Ralph Mowery
"Cecil Moore" <myc...@hotmail.com> wrote in message
news:O1vng.123149$dW3....@newssvr21.news.prodigy.com...
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.
Gerry Wheeler
news:84xng.2094$ii...@newsread3.news.pas.earthlink.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
Reg Edwards
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.
Cecil Moore
> 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.
Butch Magee
which metal but not important as long as it's conductive I guess.
Great job I bet, big bucks....
Sal M. Onella
"Dave" <no...@nowhere.com> wrote in message
news:kJKdnV2QOYIJ_wPZ...@crocker.com...
> 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.
Reg Edwards
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.
Dr. Honeydew
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
Richard Harrison
"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
Ben Jackson
> 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
<b...@ben.com>
http://www.ben.com/
Bob Bob
Did the birdless claws have any noticable effect on the match/tuning of
the antenna?
<grin>
Cheers Bob
Win
wrote:
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
Richard Fry
>>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
Dan Andersson
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 --- bollocks!
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
Frank Alforo
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.
J. B. Wood
<w0...@winlyn.us> 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: wo...@itd.nrl.navy.mil
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337
You
Then you would be.....wait for it....... WRONG........
west
west