Re: Variation of secondary Q

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Malcolm,

I have not heard back from Paul on this yet but here are some other ideas.

I could directly connect my 2.5pF 10Meg ohm probe (Tek5100) directly to the
top of the coil for a read out like this:

http://hot-streamer-dot-com/temp/PaulsQexp-3.gif

The scope could then save a data file like this:

http://hot-streamer-dot-com/temp/TEK00000.CSV

The resonant frequency drops from 84.42 kHz to 82.15kHz so the probe
loading is very low (Those are darn good probes!!  Like Pearson stuff, they
too are made out of pure money :-))).  I imagine one could back calculate
the small probe loading right out.

However, assuming  Vtop = Q x Vin  we can just input 1 volts RMS and read
out the top voltage for a direct Q reading along with time and frequency
and just have all our data there without needing to do anything but push
the save button ;-))  (may have to check for frequency variation)

http://hot-streamer-dot-com/temp/PaulsQexp-4.gif

That almost seems too easy :o)

If this is OK with Paul, it would be very easy to do.  The scope can filter
it down and over sample like 512 times to get very high accuracy.  But that
is probably over kill.  I am not sure this would be 100% OK with Paul's
paper and all, but it should be close enough I would think.

I wonder if the Q variation is not so much the coil changing but the
surroundings changing with weather?  The coil is far more stable for
temperature and humidity than the ground, walls, ceiling, etc.  Just a
thought there.

Cheers,

	Terry


At 04:53 PM 3/15/2002 +1300, you wrote:
>Hi Terry,
>           Any reason why you can't use the E-field to measure Q? 
>After all, its differences/time you are after, not an absolute figure.
>
>Regards,
>malcolm
> 
>
>On 14 Mar 2002, at 20:03, Tesla list wrote:
>
>> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>> 
>> Hi Paul,
>> 
>> I was testing this out, but I have run into a significant problem.  The
>> ring down current is tiny.  With 10V P-P in, I only get about a 200uA base
>> current signal:
>> 
>> http://hot-streamer-dot-com/temp/PaulsQexp-1.gif
>> 
>> Here is a simulation:
>> 
>> http://hot-streamer-dot-com/temp/PaulsQexp-2.gif
>> 
>> The scope only goes down to 1mA per division and the signal is flooded with
>> natural EMI being filtered out in the base current and riding on our signal
>> of interest.
>> 
>> So, the measured base current is too tiny to be useful :-(
>> 
>> Cheers,
>> 
>> 	Terry
>>