Patent GB-568915-A (GB)
Title: Improvements in radio receivers
IPC: H01Q1/24
Filed: 1943-03-18
Abstract: 568,915. Wireless receiving apparatus. ZENITH RADIO CORPORATION. March 18, 1943, No. 4406. Convention date, Jan. 16, 1942. [Class 40 (v)] A radio receiver has a loop antenna and an input circuit both tunable to the same frequency, the loop being coupled to the input circuit by a low impedance circuit having impedance matching means at each end, the overall coupling between the antenna and input circuit being small. The invention is described as applied to a portable receiver adapted for operation on a broadcast band and five short-wave bands. Power supply may be taken from batteries 44, 45, Fig. 8, or from an A.C. or D.C. supply 46 according to the setting ot a change-over switch 48, the valves being actuated by the same knob as the volume control 32. Tone control switches 27 are also provided. The receiver is provided with an extensible rod antenna 93, a broadcast loop antenna 56 and a short-wave loop 67, which may be selectively coupled to the receiving circuit of known superheterodyne type comprising R.F. amplifier 50, mixer 51, I.F. amplifier 52, detector 53 and power amplifier .54, 55 being the local oscillator. The rod antenna 93 or the broadcast loop 56 are connected directly to the grid of the first valve 50 by means of switches 98, 99, an adjustable loading coil 63 being provided for the loop 56. An outside aerial may be connected to a coil 90 closely coupled to loop 56. The short-wave loop 67, variably tuned by condensers 70, 72, 73 and switch 71, has a pick-up coil 78 connected to coils 74, 75, 7,6 in series coupled to input coils 40a ... 42a. The desired short-wave band is selected by depression of the appropriate push-button 39 ... 43 which connects the appropriate coil 39a ... 43a in the input tuned circuit, and also connects the appropriate coil 39b ... 43b in the oscillator circuit. Pushbutton 38 makes the necessary connections for loop 56. Fig. 6 shows the construction of the loops 56 and 67, which together with coupling coils 90, 78 are enclosed in dielectric casings 57, 68 hinged to plates 58 provided with suckers 59 for mounting on the window of a vehicle, thus enabling optimum orientation of the loops. The loops are connected to the receiver by leads 61, 62, 81 attached to a plug carrying the loading coil 63, the leads being maintained at a uniform separation by being mounted on the edges of a strip of stiff material. The tuning condensers 70, 72, 73 for loop 67 and switch 71 are mounted on the casing for the loop. A modified form of loop 67 is described, Fig. 11 (not shown), which comprises two loops of wire stiff enough to be supported without a dielectric casing. A constructional form of the rod antenna 93, Fig. 8, is shown in Fig. 9 and comprises telescopic sections 120, 121, the lowermost being fixed in the receiver casing 20. The inner section has a knob 122 for pulling it out, and is long enough when collapsed to extend beyond the lowest section to depress a bar 97<1> connected to switches 100 so as to disconnect the rod antenna from the receiver and connect the loops. ln a modification. Figs. 3-5 (not shown), the rod antenna. in its collapsed condition is pivoted about its lower end for stowing in the receiver casing. This pivotal movement is employed to operate the switches 100. Specification 568,944 is referred to.