Patent GB-1262647-A (GB)
Title: Radio control system
Inventor: DENCH MICHAEL JOHN
IPC: H04L5/02
Filed: 1968-05-17
Abstract: 1,262,647. Radio control systems. GEORGE RICHARDS & CO. Ltd. 12 Aug., 1969 [17 May, 1968], No. 23582/68. Heading H4L. Specification describes a pulse modulated radio frequency control system wherein by varying various parameters of the pulse train, up to six controls can be sent. When used to control a model aircraft the pulse parameters used and the aircraft element controlled may be summarized as: Element controlled Putse train parameter varied 1. Aileron Mean pulse frequency 2. Elevator Mean mark/space ratio  3. Rudder Frequency mod of mean pulse frequency 4. Throttle Frequency mod of mean mark/space ratio 5. Auxiliary 1 Amplitude of 3 6. Auxiliary 2 Amplitude of 4 The maximum frequency of variation of the aileron and elevator and thus of the pulse frequency and mark/space ratio respectively is lower than the minimum frequency modulations respectively met in the controlsignals of the rudder and throttle. Interference between controls 3 and 1 and between controls 4 and 2 is thus avoided. In the system transmitter (left hand part of Figure) a variable frequency sawtooth generator 17 has its frequency variable by two means: (a) by means of a potentiometer 18 which is set in accordance with the aileron control required, thereby setting the centre frequency; (b) by an alternating current in the frequency range 40- 80 c/s. from a multivibrator oscillator 26, having its frequency controlled according to the required rudder control by potentiometer 25. The amplitude of the alternating current, and thus the frequency deviation being controlled by a series potentiometer 32 according to the required first auxiliary control signal. The output of generator 17, in the range 400 to 800 c/s., and comprising sawtooths having vertical leading edges and sloped trailing edges are fed to a variable level trigger circuit 13. Circuit 13 produces a pulse for each sawtooth, commencing with the vertical leading edge and ceasing at a time at which the sloping trailing edge becomes equal to a variable threshold. The circuit 13 thus produces a train of pulses having the frequency of the sawtooths but with a variable mark/space ratio (i.e. pulse width). The threshold varies about an average (D.C.) value set by a potentiometer 19 according to the required elevator control with a frequency set by the output of a variable frequency multivibrator oscillator 36, having its frequency varied in the range 40-80 c/s. by a potentiometer 35 set according to the required throttle control. The amplitude of the alternating current is controlled by series potentiometer 37 according to the required second auxiliary control signal. The output of circuit 13 modulates a 27 mc/s. carrier from oscillator 11. At the aircraft receiver the output of circuit 13 is recovered at receiver 14 output. Said output is fed via saturating amplifier 15 which gives the pulses constant amplitudes, to a low-pass filter 21 having a cutoff of 20 c/s. The filter gives the D.C. component of the output, proportional to the mark/ space ratio and is then used to feed the elevator servomotor control. The cut-off at 20 c/s. blocks the pulse frequency modulation of 40-80 c/s. The pulses from saturating amplifier 15 are given a constant mark/space ratio (constant width) in monostable circuit 16 and the outut thereof is fed to a low-pass filter 22 giving the D.C. component now proportional to the mean pulse frequency. The filter also has a cut-off of 20 c/s. and feeds the aileron servomotor. The pulses from amplifier 15 also pass via a low-pass amplifier 41 (cut off 90 c/s.) to give a sinusoidal signal having the frequency of oscillator 36. The sinusoids are converted to square waves by Schmiddt Trigger circuit 42 and monostable circuit 43 and the average or -D.C. component of the resultant pulse train, proportional to said frequency and to the required throttle control, is detected by low pass filter 44 (cut off 10 c/s.). The amplitude of the sinusoidal output of filter 41, proportional to the first auxiliary control signal is detected by amplitude detector and smoother 45. The output of monostable circuit 16 is similarly fed through a low-pass filter 27 (cut off 90 c/s.) to give a sinusoidal signal, the frequency and amplitude of which, indicative of the rudder and second auxiliary controls respectively are determined in the same manner as the throttle and first auxiliary controls.