HERE IS A COPY OF MY REPLY#1048.
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Howardlong messaged me the following info.
Rise time 10-90% at the scope is 36 ps. By the time it gets to the feedpoint, it'll be about 45 ps due to dispersion in the coaxial feed.
Fall time looks similar visually but I didn't take a measurement. Pulse width is 608 ps.
Howardlong has already mentioned that his signal crosses (first reaches) to the opposite wire in 80 ps which he says accords with the speed of light for the 24 mm distance tween the pair of wires in his 450 Ohm antenna ladder line. Howardlong in effect says that this supports Veritasium's expectation that Veritasium's bulb can possibly light (start to light) in 1/c seconds (ie 3.3 ns for Veritasium's 1000 mm spacing).
These kinds of transients have at least say 4 stages.
I wanted to have a closer look at Howardlong's experiments to look at the first stage, stage-1 of his transient. But i will come back to that another day.
Today i will jump ahead & look at stage-2 of his transient.
Howardlong X using 4 ft of ladder antenna line (wires 24 mm apart). He got 12 mV, with 58 mV in the other wire, which is 20.7% (20 GHz scope).
Schantz X using 100 ft of 300 ohm twin lead antenna line (wires 7 mm apart). He got 60 mV, with 340 mV in the other wire, which is 17.6% (100 MHz scope).
AlphaPhoenix X using 1000ft of 24AWG enameled copper wire (wires 250 mm apart). He got 0.2 V, which climbed to 1.7 V, which is 11.8%(100 MHz scope). Actually his source is 5.0 V, so 0.2 V is 4.0%.
Silicon Soup (youtube) does a Finite-Difference Time-Domain simulation (1000 mm), gets a 0.3 mA signal from a 1.47 mA current, which is 2.0% 20.4%, for a mini-version of the Veritasium circuit. I don’t know how his pseudo-signal happens (its something to do with Maxwell)(displacement current perhaps).
All of the above percentages are astonishingly high. But i think i know what happens.
A step signal (voltage)(current)(Heaviside might say that the step signal is energy current)(Dollard might say impulse current)(is say elektons) propagates say to the right along the right half of our circuit, along the say bottom wire.
The bottom wire in that half is gradually flooded with negative charge (elektons), starting at the source (at the midpoint of the circuit), the flooding progressing to the right towards the short at the end.
The growing negative charge on the surface of the bottom wire gradually repels more & more free surface elektons on (along) the top wire, some go right (to the end), & some go left (to our bulb).
The elektons pushed right (along the top wire) tend to bunch up, because they are propagating in the same direction as the propagating step (in the bottom wire).
The result is that say 50% of the escaping elektons in the top wire go left & 50% go right.
The elektons propagating left create a flow of elektons flowing left through our bulb, which manifests as a voltage drop across our bulb.
Our bulb turns on (weakly) a little after d/c seconds, ie as soon as (enough) elektons start to flow (leftwards) through the bulb on our top wire.
Our bulb glows brighter as the flow of elektons through the bulb increases.
After a short time the flow through our bulb reaches its initial maximum (say 10% of the current in the bottom wire).
[In the Veritasium gedanken (wire spacing d is 1000 mm) this would be a little after 1/c.]
Eventually the step (propagating right) in our circuit will get to the end of the bottom wire & will enter the top wire (via the short), & go to our bulb.
When the main signal reaches our bulb the bulb will achieve full brightness, ie there will be a big sudden jump step in the voltage.
[In the Veritasium gedanken the main signal would reach his bulb in 1 second (his half circuit is 1 light second long).]
The elektons escaping to the left will give a current & voltage (signal) at the midpoint of our top wire (ie at our bulb). The size of the signal will depend on the wire spacing. The signal will begin to grow as soon as the E×H radiation reaches across, ie the delay is d (metres)/c (m/s), where d is the spacing, & c is the speed of light in the medium (usually air). More exactly, the delay will depend on the location of our switch, relative to our bulb.
[In the Veritasium gedanken this switch-to-bulb distance is approx the same as the spacing tween his wires anyhow.]
I doubt that a (simple conventional) LCRX lumped element transmission line model can predict transient current, using a simple LCRX paradigm, using simple speed of light.
Any such model needs smarter components.
And truer speeds (& truer flow of surface elektons).
However i have never had any hands-on experience with transmission lines, or TL models (or the application of electricity theory of any kind).
However the repulsion of the elektons from (along) our top wire is not unlike the action of lots of little capacitors tween the bottom wire & the top wire.
Perhaps someone could do a (simple conventional) transmission line model for Howardlong's experiment.
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