# Electronic circuit/inductor problems

#### Phystudent91

I'm in the opening stages of a project, part of which is building an FM Radio transmitter.
I am using the circuit found here (call it site1), which is the original of the circuit found here (site2).

On site2 is a method of making the inductors required (5 turn air coil, 4mm inner diameter with 28AWG enamel coated copper wire). I didn't have 28AWG so attempted to use 24AWG wire.

Then, to find the frequency I was transmitting at, I attempted to find the value of the inductors. Putting the inductor in series with a resistor and an AC signal generator, I could not find, at any frequency/current/voltage, any voltage across the inductor; It essentially seemed to be acting as a normal piece of wire.

I know my measuring equipment is not faulty; I've tested it all. I've used up to 2A (The max I could find on any of the equipment in my University Lab), added turns and even put a very powerful magnet on the inside of the coil to no avail.

Can anyone see a reason for this not to work?

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#### sophiecentaur

Gold Member
If this inductor is for operating at around 100Mhz, it will be a very low value of inductance. What frequency are you using for your measurement (and what value of resistor)? From your figures, it seems your inductance will be much less than 0.1μH. You can work out what the reactance of that would be at the frequency you are using for measurement - how does that compare with the series resistance value you are using? What measurement of volts across the L would you expect from this?

#### mtb856

You scraped the enamel off of the wire right? I had a problem one time where I hadn't removed the enamel enough and it wasn't making an electrical connection.

#### sophiecentaur

Gold Member
But with enamel still on the ends, the wire would be an open circuit - not a low impedance (like a "piece of wire").

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