Improvements in the transmission and reception of electric signals carrying information.

摘要

A system for the transmission of data between a stationary unit and simple mobile unit, with low power consumption, usually located on a vehicle is described. To transmit data from the stationary unit, two carrier waves, polarised, orthogonally and modulated with the data and its inverse are transmitted from antennas 12 and 13. These waves are received by a dual polarised antenna 21 of the mobile unit, demodulated by detectors 26 and 27 and passed to a summation device 28 to provide a bipolar signal with a relatively high signal to noise ratio for a micro-computer 30. For data transmission from the mobile unit to the stationary unit, the antenna 13 transmits an unmodulated carrier wave having a single polarisation. This wave is "reflected" and modulated with data to be transmitted by the mobile unit. If a data "zero" is to be transmitted, the received carrier is switched to the detectors 26 and 27, but if a data "one" is to be sent then the received signal is switched by radio frequency switches 24 and 25 along lines 22, 23 and 31 and retransmitted with a polarisation normal to that of the unmodulated carrier.