Abstract: A single side-band electrical information-transmission system is described in which the correct oscillator frequency for demodulation in the receiver is achieved by attenuating a narrow band of audio frequencies in the transmitter and automatically correcting demodulation in the receiver in accordance with the position in the frequency spectrum of this band after demodulation. Attenuation in the transmitter is carried out by a band-stop filter, and the receiver usually includes two band-pass filters, connected in parallel following the demodulator. The output from the filters is individually rectified, summed, and smoothed before being used as an automatic frequency control signal to correct the frequency of the oscillator coupled to the demodulator.