A multi-carrier V.H.F. police radio scheme

The V.H.F. police radio scheme recently installed in the county of Hertfordshire is described. The scheme is based on the principle known as Multi-Carrier Amplitude Modulation and employs two unattended, radio controlled, main stations operating on this principle. Two-way communication of a high standard is obtained between the control point and police cars in all parts of the county. The two main transmitters, radiating simultaneously with carriers as close as 10 kc/s, supplement each other without producing any areas of deterioration due to interaction. The principle and the methods employed in the scheme are discussed.