Abstract: A radio frequency transmitter having a tunable radio frequency signal generator and an amplifier coupled to the tunable radio frequency signal generator. An aerial is coupled to the amplifier and transmits the amplified radio frequency signal, which may then be received by various radio receivers. The aerial has an output voltage and an impedance. The impedance includes inductive and capacitive reactances. In order to maximize the output voltage of the aerial, an adjustable inductor is coupled to it. The adjustable inductor includes a pair of tuning coils with adjustable ferrite cores. A sampler measures the output voltage of the antenna. The sampled output voltage of the aerial is converted to a digital signal and then compared with a DC reference voltage produced by a processing unit in a comparator. The processing unit is coupled to the comparator and the adjustable inductor and receives the converted signal and analyses its amplitude.