Transistor T1 works as an audio preamplifier, gain is fixed at approximately R2/R1 or 100 times. The audio input is applied at the points LF in (on the diagram). P1 works as gain control. After amplification this audio signal now modulates the transmitter built around T2. Frequency is tunable using the trimmer CT and L1 is made using 3 turns of 1mm copper wire wound on a 5mm slug. The modulated signal passes via C6 to the antenna. A dipole can be made using 2 lengths of 65cm copper pipe. A DC power supply in the range 3 to 16 volts is required.