Patent GB-1372643-A (GB)
Title: Method of and apparatus for remote control
IPC: H03H19/00
Filed: 1972-05-01
Abstract: 1372643 Signalling over power circuits ZELLWEGER USTER Ltd 1 May 1972 [1 July 1971] 20036/72 Heading H4R  In a transmission system for remote control signals, a remote control frequency is formed at the transmitting end from a first auxiliary frequency delivered to the transmitter, the remote control frequency having a predetermined first relationship to the first auxiliary frequency, and both aforementioned frequencies are transmitted though one and the same transmission channel or through different transmission channels to a receiver, in which a second auxiliary frequency is formed from the first auxiliary frequency, the second auxiliary frequency bearing a predetermined second relationship to the first auxiliary frequency and being itself equal to the remote control frequency to a multiple thereof, and the second auxiliary frequency is delivered as clock frequency to an N-path filter to which filter is also applied the remote control frequency. The arrangement may particularly be used for signalling over power lines. The first predetermined relationship may be such that the remote control frequency f s  is a multiple of the first auxiliary frequency f H1  or a multiple of a fraction of this frequency. This may be achieved by using a rotating alternating current/alternating current converter which comprises a synchronous motor drive. Alternatively the first predetermined relationship may be such that the remote control frequency f s  is equal to the sum or to the difference between the first auxiliary frequency f H1  and another frequency. This may be achieved as described in Specification 1,145,679, when applied to power supply systems the first auxiliary frequency is mains frequency (50 Hz) and the remote control frequency generated by the frequency converter at the transmitting end is superimposed upon the power supply system, e.g. by methods known from ripple control technology. The Fig. 1 shows a receiver for receiving a control signal superimposed on the mains frequency. It comprises a first selective stage 9 for filtering out the remote control frequency f s  The selectivity of this circuit is purposely limited to allow for variations in the remote control frequency but is sufficient to eliminate any frequencies which may be harmonics of the remote control frequency, e.g. the circuit Q factor may be between 5 and 15. A highly selective N-path filter 10 is connected to the first selective stage 9. As is known the pass frequencies of such a circuit are equal to harmonics of the repetition frequency of pulses sequentially applied to transistors 34 of which there are N. A clock frequency for producing these pulses is derived from the first auxiliary frequency using a known type of frequency converter 20 functioning on the phase-locked-loop principle and comprising a phase detector 21, a low pass filter 22, a voltage controlled variable oscillator 23, and a frequency divider 24. If the dividing ratio of divider 24 is 1/B, the circuit produces an output frequency (second auxiliary frequency) which is B times the input frequency f H1  (first auxiliary frequency). The output frequency is then applied to a known N-phasic impulse generator 33 which sequentially pulses the N- transistors 34. Such a frequency converter 20 is only applicable when the remote control frequency is a multiple of the first auxiliary frequency f H1 . The arrangement must be such that the remote control frequency is equal to an integral multiple of the repetition frequency of the pulse sequence applied to the N-transistors of the N-path filter. The remote control frequency is applied to a circuit 39 after selection by N-path filter 10 which derives a D.C. output signal from the remote control signal. It follows that in the arrangement described the remote control frequency and the first and second auxiliary frequencies may vary without affecting the receiver operation providing the predetermined relationships are maintained. Specification 1,114,983, is referred to.