Ferrite Coil and Variable Capacitor - Tank Construction

The construction of the tank circuit for this one valve radio is very simple and uses the cheapest components I could find that worked well. I shall be using a readily and cheaply available 224-pF variable tuning capacitor in parallel with the coil. The required inductance of the coil is 0.408 mH for the coverage of the medium wave (MW) band, and this is approximately 70 turns of the coil around a 10 mm diameter ferrite rod. The coil is a single solid core taken out of a CAT5e wire. Since the sellers offer this in 2-meter lengths, which are not long enough, I had to make a centre tap join, hence, each section is 35 turns.

The ferrite rod is approximately 198 mm long and costs two pounds online. It is not one I am familiar with and has a slightly rough texture to the feel, however it comes from China. I have a special article Ferrite Rod Antenna Coil that you should also consult when building such coils.

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