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

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

Original poster: "Charles Hobson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <charles.a.hobson-at-btinternet-dot-com>


----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, March 09, 2001 4:57 AM
Subject: "Q" - weird... Not so high ??


> 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.

Hi Terry,

I have noticed the same "low Q" phenomena when doing somewhat similar
measurements on my small coil at around 290kHz, but by manually sweeping and
plotting the frequency vs. output from secondary. Also, I used  a dangling
scope probe and wire about a metre from the secondary for the pick up (Don't
have a spectrum analyzer). My sig. gen. had a low Z output <50 ohms. When I
placed a 470 ohm resistor in series with the feed to the primary coil, I got
the expected  high Q peaks.
For what it's worth,  Chuck


>
> 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...
>
> Cheers,
>
> Terry
>
>
>
>