Re: Measured Q

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Bart,

On 16 Aug 00, at 8:06, Tesla list wrote:

> Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> 
> 
> Hi Malcolm, 
> 
> Tesla list wrote: 
> >
> > > The skin depth of my coil is .0104 inches using the equation 
> > > Sd(inches) = (66 / sqrt(Fo)) / 25.4 
> > > 
> > > If I calc the resistive value of .0104 inch wire diameter using the same 
> > length 
> > > of wire the coil is wound at, I end up with a large resistance of 335
ohms.
> >
> > > 
> > > If I then take XL/R = 34,543 / 335 = Q of 103 
> > > 
> > > Obviously eddy currents and hysterisis are not accounted for and the
only 
> > > proper way to find Q is measurement, but this approach seems to get close
> > (or 
> > > does it?). 
> >
> > Have you measured the Q of your coil? I think it would be 
> > somewhat lower if the coil is closewound because although skin 
> > effect would be pretty well absent there would still be some 
> > proximity effect. Please let me know. I'm curious about this 
> > case. 
> >
> > Regards, 
> > Malcolm
> 
> 
> 
> 
> You know, I have never measured the Q (yes, this is embarassing. I keep
letting
> other things get in the way. I'll look through some of the posts on Q
> measurement and see if there is some method that will work for me (I
don't have
> a generator). Any suggestions? 

Wow - I can't think of any other way of doing it sorry :(
 
> I agree, that the Q is probably lower. The coil is closewound (12.75 x
44.5, 18
> awg .0418 total wire diameter, 23.4 turns per inch, Loaded Fo is 86.2kHz
> measured). I actually used a calc'd Fo in the Sd above. With the measured Fo,
> the Q here would work out to 96.4 (a little lower). I have "a lot" of top
load
> shielding going on. Unloaded Fo would work out to 87.3 (due to the higher
Fo).
> So proximity effects should make it even lower. I wonder what it really is. 

It would be *great* if you did somehow manage to measure it 
accurately. It would probably be the first time that the 
influence of the proximity effect was measured in isolation.
Is there no chance you could beg or borrow the equipment? 
You'd also need a scope and the coil would have to be measured 
with a high degree of isolation (like a minimum of 6' 
clearance from other objects all round).

Regards,
Malcolm

> I've got the secondary sitting by itself as I'm in process of some RSG
work, so
> it would be a good time to make the measurement. 
> 
> Take care, 
> Bart 
>   
>  
> 
>