This is a simple transmitter for amplitude modulation (AM) in the short wave band.
It contains three transistors. The first stage as a quartz oscillator and can operate from about 4.5 MHz
up to 12MHz. The second stage of the amplifier. For simplicity there is the resistor connected to collector and not
coil. The third transistor is traditionally connected with the coil and forms the output stage. Using a DC-blocking
capacitor it is connected to an antenna. For a simple start-up and high-quality sound it is modulated
to the last stage. Sensitivity is therefore small, and the audio amplifier is required at the audio input.
The AM modulation is built using the modulation inductor, which must have enough inductance. You can also use a secondary of
small transformer. I used the secondary of the 220V/9V 1.6 VA transformer. Double choke in the oscillator has 2x 6 turns of wire 0.5 mm on
the ferrite rod, 5mm diameter. Choke of output stage is without core and has 24 turns coil wire diameter of 0.5 mm wound on 10 mm diameter.
The circuit is powered by a well-filtered 12V voltage, current drawn is about 300mA. If you need to destroy the output power transistor,
simplest way is to switch the transmitter on without the antenna connected :).
