Qualitiy factor of an inductor

Dear friends,
I designed loop antenna for my RFID and wanted to fin out its inductance, quality factor and DCresistance. I used LCR meter and found out that L=742\mu H and Q=19.63. all measurements were made at 100KHz and that is fixed for the device. Can anyone tell me how to find the Quality factor at 125KHz since that is the working frequency of the RFID. Does the inductance change at 125KHz than it is at 100KHz?
Thanks :?

Hi there!

1) Q factor at 125 kHz: Make your coil resonate with high Q capacitor and measure 3dB points. U can use different type of setups. They all have advantages/disadvantages. Try 2 different setups to confirm you setup does not signiificantly influence Q.

2) Inductance at 125kHz: Yes it can change (it depends on self resonance and proximity effects). Let your coil again resonate with variable capacitor. Next measure your variable cap and use the resonance formula! :)

Good luck!

Thank you Darkcrusher;
What do you mean By high Q capacitor? I have the concept of of how to find the quality factor numerically. Do yo mean I make the coil resonate at 125KHz and then measure 3dB points, and find out Q? (I still have to use a resonant capacitor, 2.2nF in my case to get 125KHz resonance.)
and for the inductance, when I try different values of capacitors, do you think the coil must resonate @125KHz? or anyfrequency is permissible?
Thank you

Assuming, that the self resonance frequency is considerably higher than 125 kHz (most likely it is), the inductance won't change much to 125 kHz. Q can be expected higher by 10 to 20 percent. Checking the actual resonance frequency with a precalculated capacitor will verify the assumption.