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Topic: Calculating and making an inductor. (Read 458 times) previous topic - next topic

adilmalik

im building a Am radio receiver and i want to know how i can accurately make a coil with a specific inductance. ill be using a ferrite rod core(1cm dia).

pwillard


MarkT

You haven't a hope without the manufacturer's datasheet for that exact kind of ferrite, there are hundreds of grades.  Expect to have to experiment.  Inductances are only accurately calculated when no ferro- or ferri-magnetic materials are present (ie air-cored).
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winner10920

Or invest 20$ in an RLC multimeter off ebay
I got one and I think the minimum range was 20mH which may be to big for u but just an idea

MarkT

One problem with ferrites is that the permeability (and thus inductance) depends on amplitude, frequency and temperature  You mustn't let a permanent magnet get near it either, magnetised ferrites will change behaviour (and probably drift in permeability for ages afterwards).  Amplitude isn't an issue for a AM receiver though ;)

Either allow a lot of slack (ie have a wider-range tuning capacitor) or expect to wind a trial winding and measure the tank circuit (grid-dip oscillator is the traditional tool).  Its traditional to make the coil have an excess of windings and to fix it towards one end of the rod, since moving it will allow fine-tuning to that particular rod.  Application of molten wax to hold it once the placing is determined.
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