Patent GB-547510-A (GB)
Title: Improvements in radio-relay systems
IPC: H04B7/165
Filed: 1941-06-05
Abstract: 547,510. Automatic frequency control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 5, 1941, No. 7141. Convention date, June 5, 1940. [Class 38 (iv)] [Also in Groups XL and XXXVI] In a radio relay station which receives modulated carrier waves at one frequency and converts them for radiation to another station into frequency modulated waves of a different mean frequency, energy at the different mean frequency is used to stabilize the frequency of locally generated oscillations used in the conversion. The invention is described in relation to a system for broadcasting television signals from Station A, Fig. 1, to Station D via relay stations B and C. In this example, Station A radiates amplitude modulated waves at 45-5 Mc. which are received at B on antenna 3 and re-radiated from antenna 4 as a frequency modulated wave at 500 Mc. This is received on antenna 5 at C, converted into a 100 Mc. wave for efficient amplification and then converted to 512-5 Mc. for re-radiation from antenna 6. At D the signal is received and detected in known manner. Figs. 3a, 3b show the apparatus at C in which signals 0/500 Mc. received at 5 are converted in receiver 34 to a frequency of 100 Mc. and fed to the grid of a discharge device 35 of the inductive output type to the cathode of which is coupled the output of a local oscillator. This comprises an oscillator valve 37, frequency tripler stage 38, amplifier stage 39, second frequency tripler stage 40 and an amplifier 41 of the inductive output type. The output from 35 is at 512.5 Mc. and is coupled by means of co-axial lines 47, 51 to an amplifier 36 after which it is re-radiated from antenna 6. A transmission line TL takes energy from the output of 36 and applies it to a frequency control unit 42 for controlling the frequency of oscillator 37. Frequency control unit 42 is shown in Fig. 5 in which transmission line TL is capacitatively coupled by plates 170, 171 to concentric line resonators 152, 153 tuned to frequencies on either side of the desired operating frequency and associated with detectors 150. 151, the outputs of which are applied in push-pull to amplifiers 154, 155 the anodes of which are connected to opposite terminals of a sensitive polarised relay 157. Relay 157 acts through relays 161, 162 to control the direction of travel of a motor 159 to control the tuning of condenser 60 in the circuit of oscillator 37 in accordance with departures from the desired frequency at the output of amplifier 36. A broadly similar form of frequency control is applied to the local oscillator at station B (Fig. 2 not shown). Fig. 4 shows the high frequency converter unit 34 of Fig. 3a which comprises a detector 110 to the grid of which the signal from antenna is fed through a concentric line resonator 101 tunable by a movable piston 106. To the cathode is supplied energy from an oscillator 122 through a concentric line resonator 102 tunable by movable plates 103, and the output is taken from a transformer 108 tuned by a copper slug. Screened low pass filters 126, 127 are provided in the anode and cathode circuits of the detector 110 and oscillator 122. Frequency drift is connected by means of a vane 117 between the inner and outer conductors of resonator 102, which is adjustable by means of a motor 134, under the control of a known type of discriminator circuit fed from transmission line TL, Fig. 3a. Specification 528,817, [Group XL], is referred to.