Abstract: An automatic frequency control (AFC) arrangement for use in a symmetrically modulated, homodyne FSK receiver or transceiver forms a value representing the baseband frequency for each of demodulated data states "1" and "0" by measuring the frequency (54, 56; 80, 82) during the appropriate data state, stores it (58, 60; 84, 86) during the opposite data state, and subjects the two stored values to a subtraction process in a difference-forming means (64, 88), the output of which is then used to effect control of the frequency of the local oscillator (32). The AFC arrangement may be realized by analogue techniques, using one or more frequency-to-voltage converters and sample-and-hold units, or by digital techniques, using one or more counters and latches, or by software techniques.