Inductors and Inductance


An inductor is formed of wire coiled, with each turn insulated from the previous one. Inductors are used with capacitors to create both filters and Tuned Circuits.


Inductors that are more commonly used in radios are ‘toroidal cores’ which are small rings, which the coil is wound round, these are often used in kits as they are easily wound.


Variable type inductors come in two types the Rollercoaster, which can be found in older type ATU’s, which has a sliding contact that moves along the length of the coil as the coil is rotated, selecting more or less turns. The other type is a fixed inductor with taps connected to the coil at various points and switched. Another type has a ferrite core that can be moved with a screw thread. These are often found in tuned circuits.




Below is a table showing the units of measurement for Inductance, the Henry. I often use the Henry hoover (See picture below) whilst there is no real link it makes for a bit of fun that helps aid remembering.


Unit Name Division of Units
1H Henry 1,000 mH
1mH MilliHenry 1,000 µH
1µH MicroHenry 1,000 nH
1nH NanoHenry 1,000 pH
1pH PicoHenry


Just remember to convert up or down you just add 3 decimal places per step


Inductance and Electromagnetism


When Current (I) is passed though a wire it creates a magnetic field, when the wire creates a coil the magnetism is enhanced. Remember that a inductor stores energy in its magnetic field, this is known as Inductance, and is used to form electromagnets.


The Value of a Inductor is created by the diameter, length and number of turns the coil is made of and what sort of core is used.

As you can see by the diagram to the right there are a few different symbols for Inductors, if you can remember these now it will save learning them all later, the main ones we are concerned with for the intermediate exam are: Air-Cored, Adjustable and Iron Cored.

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