AM Radio Circuit using an axial inductor instead of an air coil

[MitchElectronics]

Hi all,

I was wondering if an axial inductor (like one shown in the image below) could be used as the inductor instead of an air coil inductor using copper wire?

All the best,
Robin

 

[betwixt]

Electrically, yes, it doesn't make much difference in what form the inductor is as long as the current is small enough not to saturate it. However, the 'Q' factor of a small inductor like that will be much lower than an air cored coil and it's own internal capacitance will make it's self resonant frequency much lower. It's DC resistance might be higher too although that depends on how thick the original coil wire is.

For what purpose is the air cored coil used?

Brian.

 

[MitchElectronics]

For what purpose is the air cored coil used?

Not sure I understand...
I was going to make a LC tank circuit for an AM receiver and wanted to use an axial inductor instead of an air coil. But aftwe what you said I will find myself a nice fat piece of copper wire with a good number of turns instead, try to increase the Q factor as much as I can.

Many thanks,
Robin

 

[betwixt]

The reason I was asking is you did not say what the inductor did in the receiver. If it is part of a low frequency oscillator circuit or a filter (IF filter for example) the construction is relatively unimportant. If it is the 'antenna' tuning circuit and responsible for signal pick-up you definitely need something bigger than those small inductors.

The self resonant frequency of small inductors like those is usually quite low due to the thin layer of insulation on closely wound turns and the epoxy resin coating over them. It means they are not suitable for high frequencies although the actual maximum will be different from one inductor to another. If your receiver is going to tune frequencies higher than a few MHz you will find them unsuitable. An open copper wire inductor will be good to several GHz, a factor of maybe 5,000 times higher in frequency.

If your frequency is higher than about 1GHz, consider silver coated copper as an alternative for even better results.

Brian.