Radio microphone bug
L1 = 9 turns on the mandrel with a diameter of 3 mm.
L2 = 100 turns on the resistor MLT - 0.25, or to increase the efficiency, it is better to take a ferrite core of grade 20 RF with a diameter of 2-3 mm and a length of 5-10 mm (its inductance must be ~ an order of magnitude larger than the inductance L1).
The initial version of the circuit was tested on transistors CT 3130A9. But, since their cutoff frequency is around 150 MHz, for the output stage I chose a very good microwave transistor 2T 657A2 (both CT 3130A9 and 2T 657A2 have SMD enclosures).
In principle, any high-frequency one (F1> 150 MHz), the same infamous KT315, fits here.
At supply voltages above 5 V, in order to limit the collector current of VT2, a resistor of 30 Ohms is switched on in series with L2.
The transmitter output power is approximately 10 mW (2T 657A2, 3 V).
The microphone is taken electret, condenser type FEM-3 or better, of course, the microphone "Pine" M1 - A2. I want to note, "Pine" does not like the supply voltage of more than 3 V.