Patent GB-955223-A (GB)
Title: Automatic control device for a radio transmitter
IPC: H04B17/18
Filed: 1962-07-18
Abstract: 955,223. Transmitter alignment. SIEMENS & HALSKE A.G. July 18, 1962 [Aug. 30, 1961], No. 27552/62. Headings H3A and H4L. In a transmitter in which a modulated signal received from a control station is amplified and transmitted, means are provided for monitoring the frequency of the control station signal and automatically realigning the transmitter in response to a change thereof. The realignment includes coarse and fine tuning of each stage of the transmitter, impedance matching the aerial and adjustment of the overall gain of the transmitter. The transmitter includes, an input stage VS to which the control station signal is applied via terminal E, a driver stage TS and an output stage ES. The control station signal is also applied to a discriminator D comprising a resistor and a variable capacitor connected in series and a comparator in which the amplitude of the voltages developed across the resistor and capacitor are compared. These voltages are normally equal but when a change in frequency is required the control station removes the modulation from its signal and adjusts its frequency to the new value whereby a difference voltage is produced by the discriminator. This is applied via amplifier V 1  to programming device Pr which switches off the H.T. supply to the transmitter and is also applied to a motor M 1  which drives the variable capacitor to a position in which the voltages are again equal. The capacitor spindle is ganged to variable capacitors C 1 -C 8  and variable inductors L 1 - L 6  whereby the tunable stages of the transmitter are roughly adjusted to the new frequency. On completion of this operation the programming device restores the H.T. supply and by operation of relays F and B connects a negative feed-back loop to earth at contact f 1  and attenuates the input signal by switching loss networks D 1 , D 2  into circuit at contacts b and f 2 . Each stage is then fine tuned in turn and for this purpose each stage, e.g. input stage VS, is provided with a phase bridge Ph 1  which produces zero output signal when a signal applied via pick-up H at the input to the stage is 90 degrees out of phase with that supplied via pickup J from the output of the stage. Coil L 1  is tuned by a drive from motor M 2 , driven by the output from the bridge via amplifier V 2 , until this condition is obtained. On completion of the individual stage tuning the output coupling to the aerial is optimized by tuning L 6  by motor M 5  which is driven by the output of comparator A 1  via amplifier V 5  when an input obtained from the anode circuit of the output value by pickup K is not in a predetermined ratio with a second input equal to the square root of voltage induced in unit W proportional to the power output of the transmitter. The programme unit then switches out the input loss circuits and restores the negative feed-back. The gain of the transmitter is then adjusted by motor M 6  driven by the output voltage of comparator A 2  which compares the input voltage and that obtained from unit W. On completion of the operation the programme unit signals the control station that the transmitter is ready for operation.