Low frequency radio transmitter. I am aware of some of the different rf modules that allow the arduino to send data at MHz. However. Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio . Transmitters in the 22 Hz range are also found in pipeline inspection gauges, also known as "PIGs". The signal is generated as an alternating magnetic Propagation · Submarine communications · Other uses · Possible health effects.