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Re: Propagation velocity in long helical coils.

Hi Bob,

	I suspended my two coils from the ceiling with heavy nylon cord and strung
a wire down to the LCR meter with the other lead of the meter grounded.  As
I approached the coils, they seemed very stable and they were not
excessively affected by surrounding objects in my case.  The distances from
other things was about 3 feet minimum.

For the small coil:
L=22.1mH (measured)
D= 4.26 inches
L= 26.125 inches
Fo measured= 351.5 kHz
Fo Medhurst= 337.1 kHz
Fo Jones= 356.1 kHz

For the large coil:
L=75.4mH (measured)
D= 10.26 inches
L= 30.0 inches
Fo measured= 146.5 kHz
Fo Medhurst= 146.3 kHz
Fo Jones= 151.11 kHz

So it looks like your formula works extremely well!!

Cheers,

	Terry

	

At 07:06 PM 05/16/2000 -0400, you wrote:
>Hi Terry,
>
>I can now include end effects because I have solved the boundary problem but
>I don't have an equation for the end C (except  Med).  However the method
>could be included in your program but it would need FFT routines.  It would
>have the advantage I think of accurately predicting the output voltage and
>coil profile voltage (for long coil).  The later would be useful for flash
>over prediction at the lower end.  It is also valid for shorter coils until
>internal self C starts to produce errors. i.e. insight into current
>profiles.
>This method could have internal C added then it would be valid for very
>short coils.
>
>-----Original Message-----
>
>
>>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>>
>>Hi Bob,
>>
>> Sorry about not getting back to you on all this.  With the holiday, list
>>problems, work....  I just didn't get to it.
>>
>>I guess the equation you found for Fo from your May 10th post is:
>>
>>Fo = 1 / (4 x SQRT (L x C))
>>
>>Where C is the "true" capcitance of the coil with the top and bottom
>>shorted (no resonance).  Is this correct?
>
>Yes but thats just a method of reducing errors caused by the ac of your C
>meter.  any accurate method will do.
>
>> I will set up a ground plane and
>
>
>The equation is for an isolated coil.  But its always best to do things
>above a definitive ground plain even so called isolated tests  i.e. as far
>as
>you can get from the plain but note the distance, correction may be possible
>later.  The ground connection  to the coil should be via a thin wire (The
>medhurst method).  Ideally two more measurements  on the ground plain and
>one half at half max height. Then we get a measurement of the ground f
>shift.
>
>>try to do this test in a large room to get an accurate true C measurment.
>>I am still doing some left over poly cap work tonight but I'll try this on
>>my two well known coils ASAP!
>>
>>Cheers,
>>
>> Terry
>>
>>
>>At 01:16 PM 05/15/2000 -0400, you wrote:
>>>Hi all,
>>>
>>>I am surprised that nobody has checked  my equation against a coil and
>then
>>>posted the results, not even Terry?
>>>
>>>I am still  trying to do some analysis on the end effects to get an
>estimate
>>>but not much success.
>>>
>>>Regards Bob.
>>>
>
>Regards Bob
>
>