How to test the Q of self-made Inductor ?

how to test inductor

hi,

I am designing a stack inductor.

The problem is how to test it. The common way is to test the inductor using network analyzer.

But also some guys using a VCO to test Q of the inducor ? Does anyone know how to do this ?

Thanks
Gang

insertion loss of inductor

Place the inductor together with a capacitor to form a resonant LC circuit.
Sweep the VCO frequency up and down of the resonant frequency and measure the voltage across the LC circuit.
Q factor can be expressed as the ratio of voltage developed across its reactive elements to the voltage injected in series with the circuit to produce the developed voltage.

testing q of an inductor

If you make a LC resonator and measure the insertion loss & BW, then you should be able to calculate the Q of the inductor by the relationship of insertion loss to unloaded Q of the components and Q of the tank.

how to test inductor

eegchen said:

hi,

I am designing a stack inductor.

The problem is how to test it. The common way is to test the inductor using network analyzer.

But also some guys using a VCO to test Q of the inducor ? Does anyone know how to do this ?

Thanks
Gang

Click to expand...

If you have a lab kit of capacitors that you know are likely to be way better than your coil (ATC A or B for instance), then I would make a parallel resonant circuit with your coil (to ground) in the band of interest and measure the resistance at resonance. Not perfect, but it is hard to argue with the simplicity. Again -- this assumes your capacitor contributes little to this resistance.

Lance

unloaded q of inductor

Thanks
you mean using a swith cap to control the resonant frequency?

Any reference to read?

vfone said:

Place the inductor together with a capacitor to form a resonant LC circuit.
Sweep the VCO frequency up and down of the resonant frequency and measure the voltage across the LC circuit.
Q factor can be expressed as the ratio of voltage developed across its reactive elements to the voltage injected in series with the circuit to produce the developed voltage.

Click to expand...

Added after 2 minutes:

thanks.
How can i get insetion loss &BW, using network analyzer ?
Best

E-design said:

If you make a LC resonator and measure the insertion loss & BW, then you should be able to calculate the Q of the inductor by the relationship of insertion loss to unloaded Q of the components and Q of the tank.

Click to expand...

Added after 1 minutes:

thanks.
But we test on wafer using probe

Lance_RFdude.com said:

eegchen said:

hi,

I am designing a stack inductor.

The problem is how to test it. The common way is to test the inductor using network analyzer.

But also some guys using a VCO to test Q of the inducor ? Does anyone know how to do this ?

Thanks
Gang

Click to expand...

If you have a lab kit of capacitors that you know are likely to be way better than your coil (ATC A or B for instance), then I would make a parallel resonant circuit with your coil (to ground) in the band of interest and measure the resistance at resonance. Not perfect, but it is hard to argue with the simplicity. Again -- this assumes your capacitor contributes little to this resistance.

Lance

Click to expand...

inductor selfmade

eegchen said:

Thanks
you mean using a swith cap to control the resonant frequency?

Any reference to read?

vfone said:

Place the inductor together with a capacitor to form a resonant LC circuit.
Sweep the VCO frequency up and down of the resonant frequency and measure the voltage across the LC circuit.
Q factor can be expressed as the ratio of voltage developed across its reactive elements to the voltage injected in series with the circuit to produce the developed voltage.

Click to expand...

Click to expand...

Well -- I was implying that you have a general idea of what the inductor value is (you can measure that) -- I often solder an inductor across a flange mount SMA connector (center pin to ground). Then you resonate this inductor with a very good capacitor. When it is resonant you can measure the resistance directly using a marker when it crosses the resistance axis of the chart.

I just find it easier to measure coils this way. Caps I usually measure in a microstrip fixture.

I believe this general method is similar to how ATC measures their caps, but instead of an inductor they use a high Q transmission line (copper pipe as I recall) -- but that is getting off topic.

Bottom line: if you measure the resistance (again, at the resonance you can read this off with a marker) and you are sure that the capacitor is much better than your inductor, you're basically measuring the equivalent parallel resistance of your coil at that frequency and you can compute Q.

There are many ways to do this, this is just one that I like for the simplicity.

Lance

self made inductor

How can i get insetion loss &BW, using network analyzer ?

Click to expand...

This may help

**broken link removed**