GB1022598A - Improvements in or relating to receivers for binary-coded signals - Google Patents

Abstract

1,022,598. Data transmission. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 20, 1964 [Oct. 18, 1963], No. 41209/63. Heading H4P. To reduce the effects of noise in a receiver in which a limiter feeds a frequency discriminator, the limiter is supplied by the received signal and by a locally generated signal having the same frequency as one of those to which the discriminator responds. In one embodiment, Mark and Space signals are received in frequency shift form. One frequency, say f 2 , is filtered out; the resultant gaps in the f 1 signal contain noise which may simulate f 1 at the discriminator. To prevent this a signal of frequency f 2 is added to the filtered signal, the added signal having an amplitude less than that of the received signals f 1 but greater than the noise level. The limiter which receives the combined signal, responding to the predominating signals, provides clean square signals at f 1 and f 2 . The received signals may be amplitude modulated. Reference is also made to a twinplex system. The local oscillator.-Fig. 3 comprises a transistor oscillator fed by a stabilized voltage, derived across Zener diode 11 from a D.C. source at 10, and by a varying voltage, derived by rectification of the filter output f 1 , fed in at 6. The amplitude of the generated oscillations f 2 thus varies within the limits specified above.