GB1425067A - Telemetering synchronization and demodulation apparatus includin an ambiguity eliminating device - Google Patents

Abstract

1425067 Digital di-phase receivers CENTRE NATIONAL D'ETUDES SPATIALES 27 April 1973 [28 April 1972 10 May 1972] 20069/73 Heading H4P A synchronizing and demodulating receiver circuit for a di-phase modulated carrier, gives a NRZ output, fed through a delay to one stage or more than one cascaded stages, each including a generator deriving clock pulses of frequency F by multiplication of NRZ output signal with the same signal delayed, the arrangement incorporating a phase locked loop, with a NRZ detector at its output. The delay may be obtained in a shift register (21) (Fig. 4, not shown) fed through amplifier (23) and 2 level limiter (24) providing a rectangular output, stepped at double frequency. The multiplier may be in the form of an exclusive OR (22) logic circuit (A+B=mod 2 sum) feeding into a phase locked loop including exclusive OR 26, amplifier (27) filter (28) and operational amplifier (29) receiving a reference voltage and oscillator (20) feeding a tapped dividing chain 19; output is taken from terminal B. The arrangement comprises cascaded chains I-III each comprising an amplifier 2, generator 3 and phase loop 4. As there are two transitions per period of the carrier frequency FO modulated by di-phase, generator 3I and loop 4I operate at 2FO which is halved at 5 to feed multiplier 6 which may be alternatively of analogue type. The modulated wave is also applied to the other input of multiplier 6 which produces a di-phase output to circuit II operating at 2F (twice bit rate) which is halved at 7 before being supplied to multiplier 8 which produces NRZ signals to circuit III at bit rate F; the main function of this circuit is to eliminate ambiguity. To reduce the noise band at the input, band pass filters 9, 10 switched by 11a, 11b are provided for each carrier; switches 12a-12c provide for alternative bit rates. It is stated that the threshold of the loop is much lower than the threshold of a system detecting transistions in a noisy message hence a greater amount of noise may be tolerated.