GB1368211A - Method and apparatus for transmitting command signals - Google Patents

Abstract

1368211 Selective signalling MESSERSCHMITT BOLKOW-BLOHM GmbH 19 May 197223775/72 Heading G4H [Also in Division H4] Analogue command signals are coded with a random (or pseudo-random) binary signal in a transmitter and transmitted to a receiver where they are stored and compared with stored references, producing a command signal when a certain measure of agreement exists, the references having been supplied from the transmitter. In a transmitter, four channels (analogue voltage inputs) are sampled in turn, repeatedly, each sample being digitized, then coded into a group of bits representing both the digital value and the identity of the channel, then supplied to a modulator via a respective shift register. The group of bits is given a pseudo-random form by feedback with modulo-two addition in the shift register (or prior to entry into the register by logic responsive to the output of a noise generator fed through a limiter). In the modulator, the bit values are each converted to one of two frequencies which are modulated on to an intermediate carrier which is then modulated on to a carrier, this carrier itself being frequencymodulated on to a carrier, this carrier itself being frequency-modulated under control of a pseudo-random sequence. The resulting signal is transmitted by radio to a receiver, e.g. in a missile, where after demodulation (including removal of the pseudo-randomity produced in the modulator) the bit stream is inserted into each of a number of shift registers (one per possible group of bits that could be sent), each shift register being correlated with a reference signal in a respective further shift register, equality being detected by a threshold switch to actuate a respective input of a digital-toanalogue converter respective to the channel to produce an analogue control output. Before launch of the missile, all the possible command signals are transmitted and loaded into the further shift registers as references, then transmitted again and loaded into the other receiver shift registers in the normal way as a check, the threshold switch outputs being sent back to the receiver. Timing circuits in the transmitter and receiver are also synchronized at this time, and the transmitter informs the receiver of the pseudo-random sequence used in the modulator. In these pre-launch operations, transmission is via an umbilical cord rather than radio. The analogue samples can alternatively be transmitted by pulse position modulation, by sending a start code-group followed after the appropriate interval by a stop code-group, the start codegroup also indicating the polarity of the sample. The code-groups also indicate the channel and have the psuedo-random feature. Since the sample may be zero and the start and stop codegroups could not be sent simultaneously, the stop code-group is delayed at the transmitter and the start code-group is delayed equally at the receiver.