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# FM and L

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#### Electronman

##### New Member
Hi,

Can I use these kind of inductors for tuned sector of FM transmitters?

Thanks

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As long as they're of the appopriate value.

Need to have both the proper current and inductance value.

Hi,

Can I use these kind of inductors for tuned sector of FM transmitters?

No, they are totally unsuitable, just wind a few turns of copper wire around a pencil for the correct type of coils.

How are the incorrect Nigel, or is it just you can't get the proper values in those form factor?

No, they are totally unsuitable, just wind a few turns of copper wire around a pencil for the correct type of coils.

Why they are unsuitable for that?

Whats the formula for doing so?
Do I need to measure Diameter of the wire, If so How exactly to do so (In metric scale)???

Thanks

How are the incorrect Nigel, or is it just you can't get the proper values in those form factor?

Too low a Q, and too high a capacitance.

Ahhh yes Q, how could I forget.
Electronman, what Nigel is saying is ideally you want an inductor to have zero ohmic resistance, so you use thick wire, but with thick wire you need fairly large physical space for the coil. Those small encapsulated inductors are very thin very closely spaced wires, so the capacitance is high and so is the resistance, basically it'll impart it's own tank characteristics on the rest of the circuit, altering the overal electrical charactoristics of the circuit.

For more math than you probably wanted but a good explanation read this.
Q factor - Wikipedia, the free encyclopedia
Towards the end of the page you'll see how it applys to tank circuits. Now what you have to do is actually determine the inductance, resistance and capactiance of one of those tiny little guys and see how it affects your circuit, because the resistance and capacitance is so high it will likley make it so that the circuit could never function. In theory if the C and R were reasonable for your particular application you could adjust the rest of the components in your circuit, but for RF applications I don't think that's really practical, way too much loss, you need a really high Q.

I said a few more words but that's exactly what Nigel was referring to.

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