Patent GB-979210-A (GB)
Title: Improvements in or relating to power conservation in travelling wave tubes
IPC: H01J25/38
Filed: 1962-03-01
Abstract: 979,210. Travelling wave tube amplifying, oscillating and supply circuits; frequency changing circuits; radio signalling; controlled non-linear inductors. WESTERN ELECTRIC CO. Inc. March 1, 1962 [March 17, 1961], No. 7961/62. Headings H3B, H3F, H3W and H4L. The collector voltage of a travelling wave tube is controlled in dependence on the helix current which is in turn dependent on input signal power. The invention enables collector power consumption to be reduced which is particularly advantageous when the tube is used in a space vehicle. Overheating of the helix is also prevented and the operating condition adjusted to compensate for tube ageing. Fig. 1 shows a magnetically focused travelling wave tube 11 having input and output connections 14, 15 coupled to the waveinteracting helix 12. The positive voltage for the collector 17 is obtained from an A.C. source 39 via a saturable transformer 31, full-wave rectifier 33 and filter 34. The helix current is derived from a D.C. supply 26 and develops a voltage across resistor 36 which is compared in a D.C. amplifier 35 with a reference voltage at 37. The circuit is arranged so that in the absence of signal input 14, the helix current is low and the current in the control winding 32 saturates the 3-limb core of the transformer 31. The collector voltage is then at a minimum value. Increase in signal power at 14 results in increase in helix current, reduced saturation of transformer 31 and a corresponding increase in collector voltage. The accelerating anode 21 is biased from a D.C. supply 25 or from the helix supply 26. In Fig. 3 a centre-tapped control winding 42 is used to compare the helix current with a reference current from source 43. A diode 45 is provided to prevent the transformer 41 responding to increase of helix current above the value of the reference current. Frequency changing; r.f. repeaters.-Fig. 5 shows a repeater for use in a space satellite communication system. Signals at 6 kMc./s. are received at 51 and mixed at 52 with a frequency f4 to give an intermediate frequency which is amplified at 54. The intermediate frequency is mixed at 55 with a frequency f3 to give the output frequency f2 which is selected by a filter 72, amplified by a travelling wave tube 57 and passed via a branching filter 58 to a transmitting aerial 59. The operating conditions of tube 57 are controlled as described above by circuit 61. Frequency #3 is provided by amplifying the output of a low-powered local oscillator 71 in the travelling wave tube 57 and feeding it back to mixer 55. Frequency f4 is provided by mixing f3 at 76 with the output of a local oscillator 75. Repeaters using a combined oscillator and amplifier.-In the repeater shown in Fig. 4, the travelling wave tube 57 has positive feedback via a branching filter 58 and a band-pass filter F3 so that the circuit oscillates a frequency #3 at the same time as it amplifies signals at f2. A limiter 62 is provided to maintain the amplitude at frequency f3 constant, despite variations of the travelling wave tube operating conditions caused by changing input signal levels as described above. The frequency f3 is fed via a directional coupler 63 to the mixer 55, so as to convert the output of the I.F. amplifier 54 to frequency f2 which is amplified at 57 and transmitted at 59 as in Fig. 5. The local oscillator 53, mixers 52, 55 and I.F. amplifier 54 may all use solid state devices.