Re: Parallel and Series LCR Circuit Qs

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

and, as I think about it.. what sort of load would you put at the far end of
the transmission line?
A short?  An open? A resistive termination (representing the thermal heating
of the air at the end of the leader)..

There is some discussion in the literature of what happens when a leader and
spark channel grows, then shrinks back (say, driven from a bipolar pulse
source).

Probably a resistive termination.  You wouldn't want a reflection back down
the line,even though, because the line has a significant resistive component
(representing the heating of the air along the spark channel), the
reflection would be rapidly attenuated.

-----Original Message-----
From: Tesla list <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Thursday, August 10, 2000 12:20 PM
Subject: Re: Parallel and Series LCR Circuit Qs


>Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>
>Hmmm.. what about modelling the spark as a transmission line.  Scaled to a
>length so that the propagation takes the right amount of time.  Just as in
a
>transmission line with an impulse, the source driving it doesn't "see"
past
>where the propagation has gotten to.  So, it would appear to have a
steadily
>increasing C, as the step function propagates down the line....
>
>The series L per unit length would be 1 uH/meter (roughly) and the C per
>unit length is 5-6 pF/meter (roughly), so the characteristic impedance
would
>be sqrt(L/C) or 500 ohms...
>
>The propagation velocity of a spark is around 1E7 m/sec, so your
>transmission line would need to be scaled to 30 times the real length
>(3e8/1E7), for a scaled L of 10 nH/meter and scaled C of .05 pF/meter
>(keeping the impedance the same...).  I'll bet you could work the
>series/parallel R in as well....
>
>you could even get fancy and hook up a bunch of transmission lines in a
>forked pattern, more representative of real sparks.
>
>This might start to have time domain properties that are realistic in a
>simple SPICE type model.
>
>-----Original Message-----
>From: Terry Fritz <twftesla-at-uswest-dot-net>
>To: jimlux-at-jpl.nasa.gov <jimlux-at-jpl.nasa.gov>
>Date: Wednesday, August 09, 2000 11:33 AM
>Subject: Re: Parallel and Series LCR Circuit Qs
>
>
>>Hi Jim,
>>
>>At 06:24 AM 8/9/00 -0700, you wrote:
>>
>>>> So the Tesla coil "source" basically needs to be impedance matched to
>>>> supply this "load", optimally.
>>>
>>>Of course, the impedance is time varying too, with the C growing as the
>>>streamer grows....
>>>
>>
>>Yes!  I assume the coil should be optimally matched when the streamer is
>>longest since that is were every bit of energy needs to be to push the
>>streamer that little bit further.  If a coil is matched for a 10 foot
>>streamer, it will not mater if the matching is poor at 1 foot.  It will
>>have no trouble getting past one foot and on to were every little bit
>>counts out at 10 feet or the edge of it's available power where fine
tuning
>>really counts.
>>
>>Of course that "may" not be theoretically the 'best' point considering the
>>other dynamics going on.  But it is my best guess...
>>
>>Cheers,
>>
>> Terry
>>
>
>
>
>