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?

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.

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.

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

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?

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?

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

"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!

"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.

"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