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Re: Dynamic Q

Hi Jim,

> Original Poster: "bmack" <bmack-at-frontiernet-dot-net> 

<snip>
> I guess the calculation is the problem. As you pointed out in my
> AC resistance post, it may be off by a factor of 2. For some reason
> I have an adversion to unloaded Q tests.  There are so many subtle
> things that can introduce errors, stray capacitance, scope probes,
> ground plane, height, orientation, etc. Considering all that, I feel
> the results may be tainted.

To only a small degree. In that series of measurements, I got the 
greatest isolation I could in a large classroom devoid of chairs.
The resonators were sniffed from a minimum distance of six feet. 
Signal generator impedance at the base was 7 Ohms resistive. That 
caused a 10% error (low) in a H/D=1 coil which when taken into 
account caused that coil's Q to reach almost 600. The Q=300 resonator
was far larger.

 > One method used was a test with the base grounded to a mesh
> plane, which in turn was earthed.  In all cases the bottom turn was 
> elevated at least one diameter above the plane.
> 
> Excitation was provided by VERY loose capacitive coupling from a
> signal generator,consisting of #20 insulated wire wraped around the 
> loose coil wire (one or two "stretch turns").  This was dressed away
> from the coil at a 90 degree angle to minimize other coupling.
> If memeory serves, a 1khz square wave worked well.
> 
> Pickup was accomplished by clipping the probe around the magnet
> wire (but not electrically connected) near the excitation point.
> 
> The coil would ring at it's natural frequency, and the periods could
> be counted and the Q calculated.
> 
> 
> The system dynamic Q was a more stable type measurement,
> owing to the top load and direct measurement.
> 
> Here I put a series resistor between the generator ( 100 to 1000 ohms)
> and the coil base lead. No, the resistor does not have any effect on the Q!

I maintain that it should and measurements I have taken show that it 
does, for me at least. Compare that resistance with the ESR of the 
coil.

 > In a few cases I tried both values for the series resistor and 
the > reflected
> load calculation came out the same!
> It's just a matter of measuring the drop across the resistor, calculating
> the current, then the refllected coil series resistance,Rs=E/I , where
> E is the voltage measured at the base.
> 
> >From this, the top relected resistance can be calclated by using
> a series to parallel conversion.  Take this RL (top) and divide by 
> the charactoristic (surge) impedance and voila!, the dynamic Q.
> 
> 
> Yeah I get around 100 for dynamic Q, but what bugs me is. this is so much
> lower than the coil's unloaded Q.  I'm running high frequency for Tesla
> stuff (900 khz +) so my Qu is high say around 800.
> 
> So what's the deal?
> 
> 
> Jim McVey

Don't know.
Malcolm