12.5 kHz channel spacing for mobile communications in the u.h.f. band between 420 and 512 MHz

The historical and technical background which lead to the development of 12 kHz channel spacing at u.h.f. is described. The advantages and disadvantages of the narrower channel spacing, including problems of achieving satisfactory adjacent channel protection and frequency stability, are discussed. A series of field tests within the London metropolitan area is reported which demonstrated that coverage and quality of reception is as good as with 25 kHz channel spacing.