There are not many AM transmitters that are easier to build than this
one because the inductor is not tapped and has a single winding. There
is no need to wind the inductor as it is a readily available RF choke
(eg, Jaycar Cat LF-1536). To make the circuit as small as possible, the
conventional tuning capacitor has been dispensed with and fixed 220pF
capacitors used instead. To tune it to a particular frequency, reduce
one or both of the 220pF capacitors to raise the frequency or add
capacitance in parallel to lower the frequency. Q1 is biased with a 1MO
resistor to give a high input impedance and this allows the use of a
crystal ear piece as a low cost microphone.
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