Patent GB-780252-A (GB)
Title: Improvements in or relating to automatic tuning control devices
Inventor: CLARKE CLIFFORD
IPC: H03J3/00
Filed: 1954-03-04
Abstract: 780,252. Electric control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 20, 1955 [March 4, 1954], No. 6386/54. Class 40 (1). [Also in Group XL (c)] In an automatic tuning arrangement for transmitters or receivers selector switches S1, S2, S3, S4 select a frequency and a motordriven tuning element LOC is driven in turn under conditions successively permitting finer control by a set of frequency discriminators and finally a phase discriminator until the tuning of an oscillator LO corresponds with that selected. The first selector S1 selects one of several stabilized frequencies of an oscillator XC1 in a range of frequency higher or lower by a predetermined amount than the range required and beats this frequency in a mixer Fl with the oscillator LO so that the difference frequency passes to a band-pass filter BPF1 of range 1-2 Mc/s. The first selector S at the same time actuates a muting contact switch MC1 energizing through switching amplifiers SWA1, SWA2, SWA3 and three relays A, B, C an amplifier MA and polarized relays SSR, MMR so that the motor M is energized. Also the tuning element LOC and selector S1 are ganged to tapping points on a self-balancing potentiometer TU whose output through the relays A, B, C and amplifier MA thus drives the motor M until a predetermined frequency within the selected frequency range, e.g. 15-16 Kc/s., is reached, when the relay SSR releases, stopping the motor, and removes a disabling bias from a switch pulse generator SPG, which subsequently fires and applies a pulse to one input of the switching amplifier SWA1. Provided also at the same time a second input to SWA1 from filter BPF1 is above a minimum value the amplifier SWA1 energizes relay A (1) to reduce the motor drive gearing in gearbox G from top to third gear by an energized lead GC3 (2), switch out the self-balancing potentiometer TU and replace it by a discriminator DM1 connected to the filter BPF1. The discriminator DM 1 is tuned to one of several frequencies selected by the second selector S2 conjointly with selecting the one of several further stabilized frequencies from oscillator XC2 preselecting the succeeding digit, e.g. 7, of the selected frequency, e.g. 15,746 Kc/s. The discriminator DM1 has a D.C. output in sign and magnitude further driving the motor M through amplifier MA until the second selected frequency range (650-750 Kc/s.) is reached whereupon the relay SSR again releases to unblock switching amplifier SWA2 and provided the output from. filter BPF1 changed in frequency by the selected frequency of oscillator XC2 in a mixer F2 and passing to a bandpass filter BPF2 exceeds a minimum value the switching amplifier SWA2 is tripped to operate relay B. Thereupon (1) the motor drive gearbox is changed from third to second gear, (2) the discriminator DM2 is switched in to replace discriminator DM1 as the output to amplifier MA. The D.C. output of discriminator DM2 (which is tuned to one of several frequencies by the third selector S3) then controls the motor M until the third fine range of oscillator LO is reached. The output of the preceding filter BPF2 frequency reduced by one of the third series of stabilized frequencies from oscillator XC3 then, if above a minimum value, energizes the switching amplifier SWA3, and relay C is energized to reduce further the gearbox gear, and replace the preceding discriminator by a phase discriminator PSR whose tuning is preselectable. The phase discriminator PSR is energized from the preceding band-pass filter TFC (the latter tunable, with 10 Kc/s. bandwidth, over the same range 105-195 Kc/s. as the discriminator DM2) and from the filter BPF2 and controls a reactance valve RV, variably tuning the oscillator LO, and rendered operative only during the final fine tuning, and acting for automatic frequency and phase control in conjunction with the amplifier MA and relay SSR also then connected to the output of the phase discriminator PSR. The final selector S4 may actuate an oscillator XC4 having only four crystals, of frequency 1857¢, 1852¢, 1907¢, 1902¢ Kc/s. respectively but each in turn varied over ranges Œ 2¢ Kc/s. by 20 condensers at 1 Kc/s. intervals from selectors S3, S4. The arrangement is such that oscillator XC3 need only be varied at 10 Kc/s. over a range 1710- 1750 Kc/s. determined by five crystals each crystal being selected twice by the selector S3. Switching pulse generator SPG.-This comprises two thyratrons SPG1, SPG4 and delivers a pulse to the switching amplifiers SWA1, SWA2 or SWA3 after the blocking bias on SPG1 is removed by the relay SSR. Operation of selectors S1, S2, S3 also momentarily earths through muting contact switches MC1, MC2, MC3, the normally biased grid of tube SPG4 to fire it so that there is insufficient time for the tuned circuit LOC to be locked by the generator SPG, when a new setting of the tuning is made, to the previous setting due to the latter being an image frequency. Switching amplifiers SWA1, SW A2, SW A3.- Comprise a normally conducting valve SWAV1 biasing to cut-off a further valve SWA2, Fig. 2 (not shown), but on a negative-going pulse from pulse generator SPG being applied through rectifiers to the grid of SWAV1 the latter is cut-off, SWAV2 conducts and any R.F. input to the other control grid of SWA2 is amplified and applied back to the rectifier in the control grid circuit of valve SWAV1 holding it cut-off provided the R.F. input is above a minimum value. Relay A, B or C then becomes and remains energized.