The two fixed coils L1 and L3 of the variable inductor are wound on a one-inch diameter plastic tube (the outer diameter of which is about 11/4 inches). The length of each coil is 21/4. The number of turns of the coil is not very important, but the general use is 86 turns of tightly wound 22 enameled wire coil.
Variable inductance tuned radio circuit:
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