Re: "Q" - weird... Not so high ??

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Terry,
         Without looking at the traces:

On 8 Mar 01, at 21:57, Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
> 
> Hi All,
> 
> I was frequency sweeping my small coil's terminal voltage response and
> noticed something...  I am loading it with a 220k resistor and the 3pF
> HV (Tek 5100) scope probe.  I am driving the primary circuit from the
> wide-band low-Z amplifier.
> 
> http://hot-streamer-dot-com/TeslaCoils/Misc/SmallCoilRvF/P3030001.JPG
> http://hot-streamer-dot-com/TeslaCoils/Misc/SmallCoilRvF/P3030021.jpg
> 
> The frequency response of the small coil swept from 200kHz to 300kHz
> looks like:
> 
> http://hot-streamer-dot-com/temp/Tek00000.gif
> 
> Since the system has dual "humps", the "Q" is "weird"...
> 
> The center frequency is 229.8kHz and the two 1/SQRT(2) freqencies are
> at 216.5 and 242.5 kHz.  Thus the Q would appear to be only 8.84. 
> This system is not terribly far from a CW coil setup.  This would
> imply that CW coils have fairly low Q too!!  
> 
> Not the 100+ Q we usually assume for CW coils, but less than 10!?!...
> 
> Comments...

By Q, are you referring to the bandwidth of the system as defined by 
Fr/(Fh-Fl)? The 100+ Q we normally talk about refers to the secondary 
alone. (Aside - those probe impedances would seriously degrade such 
measurements - endaside). If you're thinking in terms of a bandpass 
filter I'd agree but does your measurement really reflect the 
secondary's ability to store energy (or the primary for that matter)? 
I suspect some apples are mixed in with some oranges somewhere. Does 
the secondary ringdown envelope really decay so quickly? It might 
well do when loaded with your probe.

Regards,
malcolm