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

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

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

Hi Malcolm,

In this case,

The probe impedances were "fixed" to match an estimated streamer load from
the coil.  The probe's load is fairly realistic for a streamer...

Cheers,

	Terry

At 06:27 PM 3/9/2001 +1300, you wrote:
>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
>
>