Re: Measured Q (was Homemade chokes)

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Mark,

	You really need to use the AC resistance.  The skin depth and proximity
effects will raise the resistance significantly over the DC value.  Also,
the coil at resonance is not the pure inductor the equation was meant for.
The equations for an inductor in parrallel with a capacitor may be better
for a secondary with distributed capacitance.  There have been some recent
posts on all this so you could check the theory against measurments if you
can do the 125kHz resistance measurement.  However, you really need a metal
ground plan and some other "ideal" things to have the equations work out
really close.  The Q is pretty sensitive to what (or who ;-)) is near the
coil.  I can usually get to within +-50%...

Cheers,

	Terry


At 07:39 PM 8/12/00 -0500, you wrote:
>> You can calculate         Q = XL / R
>>
>> Note:       XL = 2*pi*f*L
>>
>> Where L is the inductance of the coil in Henries.
>
>Hello, list
>
>I finally decided to measure the Q of my coil.  I have a measured DC
resistance
>of 26.7 ohms.  According to E-T5, my coil's operating frequency is about
>125kHz.  The inductance is calculated to be 33mH by WinTesla.  Putting this 
>into
>the equations gives me a Q of 970!
>
>This number seems about 5 times too high, and my primary tuning isn't terribly
>finicky.  Is this high of a Q possible?
>
>Thanks,
>
>Mark B.
>
>