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Re: Discharge impedance questions. (RG-8, matching)

Hi Jim,

	The wavelength is 2980 feet at 330kHz.  RG-8 has a velocity factor of 66%
and is 26.4pF/foot.  So the cable is 0.00508 of a wavelength and 264pF.
However, I was always under the impression that if you have a 50 ohm source
and 50 ohm cable and the forward power is say 400 watts and there is no
reflected power, that you must be running into a 50 ohm real load.  In that
case, the cable length makes no difference other than phase delay.

What may be more of a factor is that I can adjust the frequency.  Perhaps
the coil's impedance will always have a 50 ohm point at some frequency.  I
turn up the power and then adjust the frequency for the lowest reflected
power possible.  I assume if 400 watts is going in, and none is coming
back, that all is well.

I just ran the impedance and phase in MicroSim,  There is a 50 ohm point
that is at an angle of 179 degrees (almost zero).  The impedance really
peaks at 92 ohms but this other point gives an almost zero reflected load
match.  Wonder if that is good, bad,...

MicroSim says I should be using 50 turns on the primary instead of 10 to
get about 50% more power to the load (resistive part).  Perhaps that would
match the resonant frequency to the impedance match points better...
Really, all we are doing is matching the 50 ohm real source impedance of
the generator to the impedance of the arc.

I am not a genius at all this load match stuff but I'll see what I can come
up with.  I'll dig up a manual to the power supply too.  I think it spent a
lot of time talking of such things.

Cheers,

	Terry


At 07:07 AM 03/12/2000 +0000, you wrote:
>
>
>> >Hi Terry,
>> >
>> >
>> >Thanks for the preliminary info!
>> >
>> >
>> >I'm afraid I don't understand the 'through about 10 feet of RG-8' part.
>> >Remember normally I speak dutch, so for us Europeans it's a little bit
>> >harder to understand the 'Tesla language'.
>> 
>> The generator is connected to the primary coil through a 10 foot long
>> length of type RG-8 coaxial cable.  A common 50 ohm transmitter cable
>used
>> for Ham radio and such.  Since I could tune the coil to almost no
>reflected
>> power, this cable should not have had any effect on anything.
>
>The fact that you got a  match was achieved at the generator end doesn't
>mean the load is matched at the other end.  A match at one end only implies
>a match at the other end if the cable is a multiple of a half wavelength.
>Otherwise, you'll want to use the formula:
>
>Zin = Z0 * (Zload*cosh(gamma) + Z0*sinh(gamma))/
>(Zload*sinh(gamma)+Z0*cosh(gamma))
>gamma is the complex propagation constant. gamma = alpha + j beta where:
>alpha is attenuation in nepers (1 neper = 8.688 dB)
>beta is length in radians
>
>(http://home.earthlink-dot-net/~jimlux/radio/tleqn.htm for more)
>
>Fortunately, your data is probably reasonably valid.  10 feet is a quarter
>wave at (18.47 meters = 16.23 MHz)... you're so much lower in frequency,
>that the cable just acts like some capacitance in parallel (160 pF I
>think.. 16 pF/foot for RG-8?  maybe 30 pF?  Don't have the chart in front
>of me).
>