Patent GB-666020-A (GB)
Title: Tuning apparatus particularly for tuning radio receivers and transmitters
IPC: H03J7/30
Filed: 1949-07-14
Abstract: 666,020. Adjusting radio apparatus. RADIO CORPORATION OF AMERICA. July 14, 1949 [July 14, 1948], No. 18607/49. Class 40 (v). A circuit, particularly an early stage of a radio receiver having a pre-selected L.O. frequency, is tuned to a desired frequency by setting up oscillations in the circuit, changing the frequency of the oscillations and correspondingly the tuning of the circuit and interrupting the tuning when the desired frequency is reached. The oscillations may be set up by causing the circuit to self-oscillate or by injecting oscillations into it. The invention is described with reference to a 10-channel superhet receiver, Figs. 1 and 2 (not shown), in which the operation of the channel selector switch causes a motor to clear the previous tuning settings, to select by means of switches the desired I.F. frequency and local oscillator crystal or crystal harmonic and finally to adjust the variable tuning capacitor of the R.F. circuits to a frequency corresponding to the particular I.F. and L.O. frequencies selected. Adjustment of I.F. and L.0. selectors.-The selector switch SS, Fig. 6, when rotated to change the channel operates a reversing relay RR2 (shown in two parts) which releases relay RR4 by means of contact 76 and operates relay RR1 which is locked in by its contact 88 and provides a holding circuit for relay RR2 during clearing. In this condition the supply is connected to the motor field (MFLD) via a contact 70 and to the motor armature via contacts 75, 78, 80, 87 and the armature accordingly rotates. In addition magnetic clutches MC1 and MC3 are operated to cause selectors 30, 31, 32, and HS to rotate to the desired crystal and band position and also to drive the R.F. tuning capacitor 34 towards the L.F. end of the range. The initial movement of the motor releases a switch 82 which provides a holding circuit for clutch MC1 for use when relay RR2 is released. When the lowfrequency tuning limit is reached the friction clutch FC2 driving the tuning condenser 34 and arm 94 slips but arm 94 makes contact with a point L.F. to operate relays MR (shown in two parts) and-K16, the former providing an alternative circuit at 73 for the motor field for use when relay RR1 is released. After a predetermined time the previous settings of the selectors have been cleared and a delay switch 84 operates releasing relay RR1, maintaining the break in its circuit until the hunting switch HS breaks the circuit of relay RR2. This releases the R.F. tuning clutch MC3 and operates relay RR4 which reverses the direction of rotation of the motor. A ratchet device however prevents the motor driving the hunting switch in the forward direction. The initial part of the forward movement re-operates the switch 82 which breaks contact 83, releasing clutch MC1, leaving switches 30, 31, 32 and 37 at the desired setting. The switch also operates a clutch MC2 which accordingly drives a bandchanging switch 33 to the desired setting when the clutch is released and a contact 86 on the clutch completes the circuit for clutch MC3 and the tuning of the R.F. circuit commences. R.F. circuit tuning.-When tuning capacitor 34 reaches the lower end of its range (as described above) contact arm 94 contacts point L.F. and operates a relay K16. This operates a relay K12 which operates a relay K2, Figs. 3 and 4 (not shown), causing either the R.F. stage to oscillate or starting an oscillator operating at the resonant frequency of the R.F. tuned circuits to which it is coupled and whose tuning capacitor is ganged to the R.F. tuning capacitor. A relay K7 is also operated by relay K12 and this renders operative a normally conducting valve 9 whose grid is connected to a rectifier supplied either from the I.F. amplifier or, where a C.W. heat oscillator is provided, from the A.F.. amplifier and whose anode current operates a relay K13. The tuning continues at a rapid rate until it passes through and beyond the desired point when the momentary release of relay K13 by the I.F. or A.F. output momentarily releases relay MR operating relay RR4. Relay K16 is .slow to release and remains operated. Contacts of relay RR4 reverse the connections of the motor field M and insert a resistor R in the field circuit so that the motor slowly returns the tuning to the desired tuning point. Relay K13 again releases at this point and stays so for a sufficient time for relay K16 to release as well as relay MR. The latter disconnects the motor field supply and releases the tuning clutch MC3. Relay K16 releases relay K12 to render valve 9 inoperative and releases relay K2 (not shown) to restore the R.F. stage to its normal condition. Switch 36 prevents the tuning being stopped by spurious responses of the receiver, e.g. at the image channel. In an alternative arrangement for adjusting the R.F. tuned circuit (Fig. 7) the tuning capacitor 34 is driven by motor M rapidly in one direction through a gear 61 and the clutch MC3 as before, but the final slow adjustment is effected by a slow reduction gear 63 and forward and reverse shafts SH2 and SH3. These shafts are brought into operation by clutches MC4, MC6 when the contact of a relay 58 is moved from its neutral position by unbalance of normally balanced valves 56 and 57 caused by the A.F.C. voltage applied from a discriminator 52 to the grid of valve 56. The relays K12 and K16 are operated in this modification by a relay 59 in series with the supply to clutches MC4 and MC5.