Carrier telegraph system using frequency modulation

The system provides up to 19 high-quality full duplex teleprinter circuits, within the range 300-2750 c/s, over physical, carrier, or radio links. Transmitting and receiving circuits are described with diagrams. At 60 w.p.m. the peak distortion is 1.5-4.0%; at 100 w.p.m. it is 4.0-9.0%. The effects of (a)slow and sudden signal variations,(b) noise, and(c) variation of signal frequency, are shown to be small compared with similar effects in amplitude-modulated systems.