Medium and shortwave transmitter 1...21.4Mhzjust a neglectable small) frequency drift. The frequency can be changed by changing the crystall in the oscillator, and aswell, changing the value of the coil in the output / pi filter network. This transmitter offers a transmitting range from 50cm (medium wave) up to 8 meters (12Mhz) depending on how and where the transmitter and antenna is set up and how sensitive the receiver is. The transmitter has a built in audio amplifier, so you can use it either with microphone or with external audio source. In the case of using this transmitter with an external audio source, an opto coppler is used to disconnect the transmitter circuits high frequency parts of the audio source. That ensures that the audio source won´t get affected by the transmitter, and also, the antenna matching network works more reliable. The sound quallity from the transmitter is pretty good and clear. You can find the circuit diagramm from the transmitter here:
