Patent GB-490206-A (GB)
Title: Improvements in or relating to tuning controls for radio receivers
IPC: H03J1/10
Filed: 1936-12-08
Abstract: 490,206. Adjusting wireless apparatus. WARDLE, P. G., JALES, F. G., and METCALFE, C. Dec. 8, 1936, No. 33696. [Class 37] A radio-receiver comprises a main tuning device which at predetermined positions throughout its range of movement permits band spread tuning means to be brought into operation, whereby finer tuning and a more open or band spread scale over narrow wave bands at these predetermined positions may be provided. The invention is particularly applicable to short wave reception where the majority of the desired transmissions are massed together in bands at about 14, 16, 19, 25, 31, and 48 metres, respectively. In the embodiment shown, an all wave receiver, tuning in the long and medium wave bands is effected by a knob 7 which through a sleeve 6 and friction reduction gearing 8a-8b, 9, 11a-11b, 12 drives the main tuning condenser shaft 13, the tuning pointer 20 rigid with a reduced portion 13a of shaft 13, co-operating with a fixed scale plate 21. For tuning in the short waves (14-50 metres) the knob 7 adjusts the main condenser 14 in the same way, the pointer 20 co-operating with a line 21a on the scale plate. On this line are points 21e, 21 f, 21g .. &c., the band spread tuning means being permitted to come into operation when the pointer 20 coincides with one of these predetermined points. The band spread tuning means comprises a variable condenser 35, adjustable by a knob 27, Fig. 2, through shaft 25, and a tensioned sprocket chain 30 looped around a wheel 28 on shaft 25, a wheel 33 on the adjusting shaft of the condenser 35 and a wheel 31 on a sleeve 31a, whereby a pointer 32 rigid with the sleeve is moved over a band spread scale 21h on which the station names are marked directly, or station indicia provided and interpreted with reference to a key list such as 21j, the scale 21h, list 21j and corresponding spot 21g for example, being similarly and distinctively coloured so that they may readily be distinguished from similar band spread scales and key lists provided for the other spots 21e, 21c &c. The band spread tuning condenser 35 is connected in parallel with the main tuning. condenser 14 and the arrangement is such that the band spread tuning device can only be operated when the main tuning pointer 20 coincides with one of the points 21e, 21# .. &c., and that the tuning pointer 32 must be brought back to the zero position, shown, before the main tuning device can again be operated. For this purpose; a flanged locating disc 41, Fig. 3, rigid with the main tuning condenser shaft 13, has a series of slots 41b in the flange 41a. During adjustment of the main tuning condenser 14 the flange 41a rotates in a slot 42a in a setting disc 42 rigid with a shaft 44 so that when the pointer 20 registers with one of the spots 21e, 21 f .. &c. the corresponding slot 41b in the flange 41a registers with the slot 42a. The band spread tuning condenser may now be operated from its zero position by knob 27, which in addition, through shaft 25, worm 29 and wormwheel 45 rotates shaft 44. The disc 42 therefore enters the slot 41b in the flange 41a and prevents adjustment of the main tuning device 14 until the band spread tuning device has been returned to its zero position determined by a nose 47 on the disc 42 abutting against the disc 41. Modifications. The band spread tuning mechanism may be locked against movement when the receiver is operating in the medium and long wave ranges, by associating a disc such as 41 with the wave range switch, the disc having only one slot and co-operating with a slotted disc on shaft 44 to permit rotation thereof only during short wave reception. This would also prevent operation of the wave range switch except when the band spread tuning device is in the zero position. Other locking means may be employed, and the band spread condenser 35 may be biassed towards its zero position by a spring. The flange of the locating disc 41 may be omitted and the slots, such as 41b, formed radially therein with resilient sides. These slots may be formed in blocks adjustably mounted on the disc 41. The ranges covered by the band spread tuning device corresponding to the various settings of the main tuning device may overlap so that, in effect, the whole of the short wave band can be spread out. The pointers 20, 32, may be replaced by cursors linearly movable by endless cables and cooperating with curtain or band type scales, or the cursors could be fixed and the scale bands movable, the band spread scales then being moved successively into operative position. Lamps may be lit as the pointer 20 reaches the predetermined points 21e, 21 #, &c. to indicate that the band spread tuning device may be operated and to illuminate the corresponding scale. The scales could be optically projected on to a viewing screen and selectively illuminated. In another embodiment each variably tuned circuit includes the main variable tuning condenser 14, Fig. 6, in parallel with a portion of inductance 55, the remaining portion of which is short circuited through a tapping 56a, switch 58, line 59 and a line 60 connected to line 59 at 60a. At the predetermined positions in the main tuning range the switch 58 is automatically moved to connect one of the tappings 56b . . . 56g to line 60 which is simultaneously disconnected from line 59 to insert a small condenser 57 in series with condenser 14, whereby, during subsequent adjustment of the main condenser 14 over a predetermined range, the main pointer itself 20 is read against a band spread scale arranged on the main scale. In this case the pointer 32 is dispensed with. The condenser 57 could, alternatively, be replaced by a small variable condenser in parallel with the main condenser 14, the tappings 56b . . . 56g being arranged, in this case, above tapping 56a. In another embodiment, a small band spread condenser such as 35 is adapted to be inserted in a tuning circuit switched in to replace the main tuning circuit, at the predetermined points in the main tuning range. In the arrangement shown in Figs. 1, 2, the condensers 14, 35, may be combined, for example, they may be arranged coaxially with the movable plates of condenser 35 co-operating with the fixed plates of condenser 14. In another embodiment the band spread tuning means could be arranged to rotate both the movable and normally fixed plates of the main condenser 14 in the same direction but at different speeds to get the band spread effect.