On 20 Mar 2004 23:28:38 -0800, (John Michael
Williams) wrote:

Ships around the turn of the 20th century transmitted morse code by
spark, I think.

The Lusitania, Mauritania, Titanic, and Olypic all ran on coal. No
gasoline in sight. Later vessels ran on bunker C fuel oil, which is
more like tar than gasoline. I don't think one has to worry about
sparks on such a vessel unless it's finely devided coal dust, which
finished off the Lusitania in a secondary explosion after the torpedo.

Interesting idea. I would have thought that a tube would require
more V than a neon lamp to get started. I'll try it if I can
find a lamp.

Neon lamp needs about 60 volts to light and 40 volts to stay lit. The
4 watt flourescent tube wants at least 90 volts to start, and I think
(i.e. guess) about 50 volts to stay lit.

What you seem to be suggesting is that I simply connect the
lamp to the 1/4 wave receiving antenna, right? Why introduce
my hand? For ground on the other lamp contact?

Yep. You're the ground. You should be fine with a 5 watt CB and a 1/4
wave whip. The high voltage point is near the tip. However, don't
try it with an illegal CB linear. You'll get an RF burn for your
troubles.

Incidentally, there are cell phone antennas with lights in them.
http://cellphones-accessories.com/12stobligcel.html
They're LED's which require much less power to light than a 4 watt
flourescent bulb. Still, it's kinda interesting.

I don't see the point of attaching a long
wire to the CB, because they don't come with long bare wires.
Clearly, I could get a good spark by attaching a wire to the
CB batteries, and avoid all the RF stuff!

Exactly. Same with an open relay contact or toggle switch. However,
don't foget that you need containment to create an explosion.
Sparking the DC inside the trunk is the mostly likely location.

22 V is a lot more than I could get with a 1 m monopole: I only
got 100 mV peak to peak.

The 22 volts peak is at the RF connector. I'm assuming that if there
is a spark gap, it will be in the coax cable or associated antenna
connectors.

It appears my 1 m wires
were too short; but, if I use a long wire, the distance from the
transmitter will lower the power transfer to some
of the wire, won't it? Or, I'll have to move away, into the
far field--but that will also lower the power.

Inverse square law. Double the distance, and you get 1/4 the power.
For a fix load resistance, 1/4 the power is 1/2 the voltage. However,
you'll get vary bad coupling efficiency with such an arrangement. I
could grind the near field equations but you'll never get ALL the
power (5 watts) delived to your random wire pickup. Think resonance
and close coupling if you want to do better.

There's no question 5 W is enough to make a spark of arbitrary
size, given an inductor somewhere around, but I don't see where
the 50 ohms comes from, if I'm looking for a spark caused by the RF?

That's the approximate impedance of the antenna as found on a typical
mobile installation. Again, I'm assuming that if there is a spark to
be found, it will be at the coax ends or connectors. They're all 50
ohms.

The transmitter antenna is coated with about 3 mm of rubber; I think
cell phones are the same way. A spark has to come from the RF,
I think. There is a BNC connector, but that implies complete
shielding (even flame suppression!) at the antenna base.

A BNC connector is quite open but is good for maybe 150 volts of RF.
However, all it takes is a sloppy coax connection, with some of the
braid wires slopped around near the center pin of the BNC, and you
have a potential spark gap.

I have a telescoping antenna intended for a receiver that is bare
metal, though. I could substitute it.

Won't make much differnce. At 0.001" gap necessary for a spark with 5
watts can only happen with a defective installation.

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

I beg to differ. The ignition of a gasoline oxygen mixture requires a
specific amount of energy to ignite. Anything less will not produce
the requiste chemical reaction. Think spark plug heat ranges and glow
plugs in model airplanes. I'll grind the numbers if you want, but
it's now midnight, I'm tired of waiting for Windoze update, and I'm
going home.


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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
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