On Sun, 21 Mar 2004 08:47:34 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in mppp50ho4dr08ahkb3dlbqkcfkp0ih
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.

I didn't know that it wasn't linear. I just assumed that it takes the
same amount of energy to peel electrons off of a single atom (ionize)
regardless of gap seperation. A wider gap requires more voltage to
ionize more atoms to create a longer conduction path, but the energy
per atom is the same. I also couldn't find (Google) any useful
references that showed this non-linearity. Unless the heat generated
by the ionization contributes to assisting furthur ionization, my
seat-o-de-pants physics says it should be linear (for DC).

There's also the minor detail of RF excitation versus DC. As I
vaguely remember from my 35 years ago college welding classes, TIG
welding uses RF to strike the arc because it takes less
power/energy/whatever to start the arc. We're allegedly talking about
striking an arc across 0.001" with a 5 watt, 27MHz transmitter
terminated with a 50 ohm load. If it's non-linear in the opposite
direction, the calcs are gonna be no fun.

I have everything it takes to test this. Microscope slide, with two
sewing pins glued with hotmelt goo and seperated by 0.001". Apply RF
and watch through the microscope. I'll see if I can throw something
together and post photos (time permitting).

Also, I've always been tempted to build a low power, QRP spark gap
transmitter. Although the mode is illegal, I suspect that operating
spark at below Part 15 incidental emission standards, would be
tolerated. Getting the arc to start at such low power levels might
require some exotics (i.e. piezoelectrics). This could be the start
of something interesting (or disgusting).


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
(831)421-6491 pgr (831)336-2558 home
http://www.LearnByDestroying.com AE6KS

I read in sci.electronics.design that Jeff Liebermann
wrote (in c1tr509eqipks7lt08ttt5cvnpkumu
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
I didn't know that it wasn't linear.


Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

On Sun, 21 Mar 2004 23:00:47 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in c1tr509eqipks7lt08ttt5cvnpkumu
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
I didn't know that it wasn't linear.

Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)

Yep. That's it. Thanks. Haven't seen that since kollege. Also saw
your comments on the topic in other usenet news articles. So much for
my simplified view of ionization.

Online spark gap calculator:
http://www.cirris.com/testing/voltage/arc.html

Minimum breakdown voltage in air at STP is about 350VDC. For RF, that
would be:
350 * 0.707 = 192 Vrms
Into a 50 ohm antenna at the coax connector,
P = E^2 / R = 192 * 192 / 50 = 737 watts
for any size spark gap. I don't know of any kilowatt cell phones
around, but that's the power output needed to arc at the antenna
connector. It might be somewhat lower due to the effects of RF vs DC.
Also a suitably weird antenna could be fabricated to dramatically
increase the voltage at some point. However, those coils are usually
up in the air where they cannot get close to a ground suitable for
forming a spark gap.


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
(831)421-6491 pgr (831)336-2558 home
http://www.LearnByDestroying.com AE6KS

Jeff Liebermann says...

John Woodgate wrote:

Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)

Yep. That's it. Thanks. Haven't seen that since kollege. Also saw
your comments on the topic in other usenet news articles. So much for
my simplified view of ionization.

I am removing Mr. Woodgate from my killfile. I was under the
impression that he only wanted to post about politics in the wrong
newsgroup, but obviously I was wrong. My apologies to Mr. Woodgate.


--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/

Jeff Liebermann wrote in message . ..
On Sun, 21 Mar 2004 23:00:47 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in c1tr509eqipks7lt08ttt5cvnpkumu
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
I didn't know that it wasn't linear.

Google for Paschen's Law. For high voltages it is linear enough for
calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)

Yep. That's it. Thanks. Haven't seen that since kollege. Also saw
your comments on the topic in other usenet news articles. So much for
my simplified view of ionization.

Online spark gap calculator:
http://www.cirris.com/testing/voltage/arc.html

Minimum breakdown voltage in air at STP is about 350VDC. For RF, that
would be:
350 * 0.707 = 192 Vrms
Into a 50 ohm antenna at the coax connector,
P = E^2 / R = 192 * 192 / 50 = 737 watts
for any size spark gap. I don't know of any kilowatt cell phones

Then again, some users seem to be able to put in kilohours of talk.
Does that count? (just kidding).

Seriously, into air at the antenna,

P = E^2/377 ~= 97 W.

A very sharp tip would create an additional gradient,
which suggests trying to spark with a sharpened antenna against
something metallic at AC ground.


around, but that's the power output needed to arc at the antenna
connector. It might be somewhat lower due to the effects of RF vs DC.
Also a suitably weird antenna could be fabricated to dramatically
increase the voltage at some point. However, those coils are usually
up in the air where they cannot get close to a ground suitable for
forming a spark gap.

John

John Michael Williams

In , Jeff Liebermann wrote:
On Sun, 21 Mar 2004 08:47:34 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in mppp50ho4dr08ahkb3dlbqkcfkp0ih
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.

I didn't know that it wasn't linear. I just assumed that it takes the
same amount of energy to peel electrons off of a single atom (ionize)
regardless of gap seperation.

It gets messy. You can see how messy it gets when you see what happens
in the cathode area of a "glow discharge".

A "glow discharge" is one of two common processes where positive ions of
the gas/vapor are accelerated by the cathode-adjacent electric field into
the cathode material, and where positive ions bombarding the cathode
dislodge electrons from the cathode to maintain the supply of free
electrons in the "discharge" (conductive path of glowing gas/vapor).
(The other of the two common discharge mechanisms where cathode
bombardment by positive ions dislodges electrons is the "cold cathode
arc". There is still another cathode process for a discharge known as the
"thermionic arc".)

The glow discharge cathode process has 5 layers, 3 dim/dark and 2
bright. There is some sort of 'natural spacing' and 'natural thickness'
of these layers, which varies with gas/vapor type and pressure and the
cathode material. There is also a characteristic voltage drop of the
cathode process known as the "cathode fall", and that is normally a few
times or several times the ionization potential of the gas/vapor.

There is such a thing as "normal glow", where the cathode process occurs
at its natural current density (for the gas/vapor type and pressure and
cathode material), and the first two dark layers and the two bright layers
and some minimal portion of the third dark layer have a tendency to occupy
some 'natural distance' (a function of gas/vapor type and pressure
and cathode material) between cathode and anode.

Then there is "abnormal glow", where the cathode process is forced into
a smaller space between electrodes and/or is conducting a current density
higher than 'natural' (for the gas/vapor type/pressure and cathode
material) due to more current flowing than is "natural" for the available
cross section of cathode process. When that happens, the "cathode fall"
is even higher than that of "nowmal glow".

There's also the minor detail of RF excitation versus DC. As I
vaguely remember from my 35 years ago college welding classes, TIG
welding uses RF to strike the arc because it takes less
power/energy/whatever to start the arc.

I don't know about that, but I have heard of RF glow discharges maybe
having the cathode process eliminating one bright layer and one dark layer
(for "electrodeless discharge" that occurs where insulation exists over
the cathode for example), and that may reduce the cathode fall.

We're allegedly talking about
striking an arc across 0.001" with a 5 watt, 27MHz transmitter
terminated with a 50 ohm load. If it's non-linear in the opposite
direction, the calcs are gonna be no fun.

at best!!!

I have everything it takes to test this. Microscope slide, with two
sewing pins glued with hotmelt goo and seperated by 0.001". Apply RF
and watch through the microscope. I'll see if I can throw something
together and post photos (time permitting).

Please do!!!

- Don Klipstein )

Jeff Liebermann wrote in message . ..
On Sun, 21 Mar 2004 08:47:34 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Jeff Liebermann
wrote (in mppp50ho4dr08ahkb3dlbqkcfkp0ih
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.

I didn't know that it wasn't linear. I just assumed that it takes the
same amount of energy to peel electrons off of a single atom (ionize)
regardless of gap seperation. A wider gap requires more voltage to
ionize more atoms to create a longer conduction path, but the energy
per atom is the same. I also couldn't find (Google) any useful
references that showed this non-linearity. Unless the heat generated
by the ionization contributes to assisting furthur ionization, my
seat-o-de-pants physics says it should be linear (for DC).

You need to read up on the physics involved. The critical point is
that a free electron in the gas has to have a long enough mean free
path to pick up enough energy by falling down the electric field to be
able to ionise a molecule when it does hit one, generating one more
electron in an inelastic collision.

If it hits a molecule before it acquires enough energy, in an elastic
collision, it will end up travelling in a different direction with the
same energy, but with a good chance of losing the energy that it had
accumulated. Think "drunkards walk".

The minimum in the Paschen curve corresponds to the point where the
mean free path is longer than the gap.

There's also the minor detail of RF excitation versus DC. As I
vaguely remember from my 35 years ago college welding classes, TIG
welding uses RF to strike the arc because it takes less
power/energy/whatever to start the arc. We're allegedly talking about
striking an arc across 0.001" with a 5 watt, 27MHz transmitter
terminated with a 50 ohm load. If it's non-linear in the opposite
direction, the calcs are gonna be no fun.

RF excitation works better than DC becasue it doesn't sweep the
electrons out of the gap as they are created (by cosmic rays or local
radioactivity) in the way that a DC field does. Like I said earlier,
the physics was worked out about a hundred years ago, and the
calculations shouldn't be too difficult now that we can use computers
for the tedious bits.

I have everything it takes to test this. Microscope slide, with two
sewing pins glued with hotmelt goo and seperated by 0.001". Apply RF
and watch through the microscope. I'll see if I can throw something
together and post photos (time permitting).

Everything except a sound undertanding of the theory. I've got a copy
of a reprint of volume 2 of "Conduction of Electricity Through Gases"
- Ionisation byCollision and the Gaseous Discharge - by J.J. Thompson
and G.P. Thompson.
My copy was published by Dover Press in 1969, and reprints the 1933
third edition. The first - singe volume - edition was published in
1903. I bought it when I was fiddling around building a starter for a
xenon arc lamp, back in 1972. It proved quite useful.

-------
Bill Sloman, Nijmegen