2019-03-22 Tuned Circuit For 702 kHz

from FB group Building Transistor Radios

Stoffel van Aswegen
I used the free Android app ElectroDroid to do these calculations. For 702 kHz, a 220 pF fixed capacitor (NP0 or C0G) and a 230 microhenrys coil are needed. The standard ferrite loopstick is 230 uH, but you can wind your own on a coil form such as a toilet paper roll. For a TP roll 44 mm diameter and coil 70 mm length, it takes 92 turns. But beginning at the 85th turn you make a tap every 2-1/8 turns, up to about 100 turns. Then you can connect the capacitor to one of the taps to tune the circuit to the right frequency.

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