Patent GB-508304-A (GB)
Title: Improvements in or relating to radio receivers and the like
IPC: H03J5/14
Filed: 1937-12-24
Abstract: 508,304. Adjusting wireless apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 24, 1937, No. 35822. Convention date, Dec. 24, 1936. [Class 37] [Also in Groups XL and XXXVIII] A radio receiver is tuned by indirect means including a tuning chart having a strip of flexible material bearing a list of station names and means whereby a characteristic potential, appropriate to effect tuning of the receiver to a desired station, is derived from a source of potential by pressure of the finger tip upon the desired station name, thus associating the flexible strip with the means for deriving the characteristic potential. The primary selection may be made in two stages, the first selecting a range of frequencies, the second a particular frequency in that range. Thus, in, Fig. 2, the fine selection system comprises a resistance 141 connected across a source of potential from which a potential, characteristic of a desired station, is obtained from a contact 153 and impressed on the condenser 150. The valve 152 has in its anode circuit a two-way relay 148 actuated in one, direction by a fall and in the other by an increase in the anode current. This 'relay controls a tuning motor 147, Fig. 5, to run in either direction corresponding to the sense of operation of the relay; the tuning motor also causing contact 154 to move along the balancing resistance 161. The potential applied to condenser 150 is impressed on the grid of valve 152 over a onevolt battery and diode 157 which is normally conducting. The potential of the grid of 152 is normally negative to that of its cathode, and that of contact 154, by its fixed bias added to the one-volt source referred to. If now a lower voltage is applied to condenser 150 (i.e. if contact 153 is momentarily connected lower down the resistance 141) the negative grid potential of 152 diminishes and the relay operates in one direction ; the tuning motor then runs to vary the tuning until the motoroperated contact 154 has rebalanced the D.C. bridge 141, 161 when the motor stops. If the voltage applied to the condenser is higher than its previous value the diode 15 becomes non- conducting and the relay 148 is actuated in the opposite sense to switch in the motor for reverse running. The selection of the characteristic voltage from 141 to correspond with a particular station is effected by means of a tuning chart shown in Fig. 1. This comprises a series of panels 144 each carrying station names grouped in order of increasing frequencies and selectively illuminated by push-buttons 133. The chart index or pointer may be effected by a moving beam of light projected on the scale from a mirror drum on the tuning shaft ; or a projection system may be employed to illuminate, inside a rectangular slot, the name of the station selected. The panels 144 are of transparent flexible material, each secured at each end or along one side to an insulating bar 142 as shown in Fig. 3. A fixed translucent plate 143 carrying the station names is mounted behind each panel. Along the entire free edge of each panel runs a conducting strip 145 constituted e.g. by a narrow silvered deposit. The control resistance 141 is wound on a narrow former and its length is co-extensive with the strip 145 with which it co-operates. Thus, on touching a station name with the finger tip the conductor 145 (which is the contact line 153 of Fig. 2) contacts with the resistance 141 to give condenser 150 its characteristic charge. The coarse or range selection system is shown in the left-hand part of Fig. 2 and acts in a similar manner to the fine selection system described above ; a characteristic range potential from resistance 151 is impressed on condenser 160 and the valve 162 is controlled to operate relay 148 through valve 152 by applying high-frequency voltage to 162 from an auxiliary source, rectifying the resultant output modified by the charge on 160 and applying the rectified voltage at 155 in the fine selection system. A re-balancing resistance 171 completes the range selection bridge. Fig. 5 shows the diagrammatic arrangement of the range resistance 151<SP>1</SP>, sections of which are selected by contact strips 140 and 1451 analogous to those of the fine system 141, 145. The re-balancing potentiometers 1611 (fine tuning) and 171 (range tuning) are operated at different speeds by the tuning motor 147 through gears ; CVS represents the tuning condensers. The indirect tuning system described may be supplemented by automatic frequency control to give final accuracy of tuning.