Abstract: A shortwave radio-receiver shows an improved reception sensitivity that can be used in a highly convenient way. The receiver is adapted for the superheterodyne system and the PLL synthesizer system and includes a front end circuit 33A for converting the received shortwave signal into an intermediate frequency signal. It also includes a formation circuit 50 for forming a tuning voltage VMB to be applied to the variable capacity diode of the antenna module and a jack J32. When the antenna module is in use, the formation circuit 50 is controlled in response to the reception frequency of the front end circuit 33A so as to modify the tuning voltage VMB and make the latter correspond to the reception band of the received shortwave broadcast to be received. The tuning voltage VMB is applied from the jack J32 to the variable capacity diode and, at the same time, the received signal is fed to the front end circuit 33A.

Abstract: A double super-heterodyne receiver has a high-frequency input circuit that includes a high-frequency amplifying device, a low-pass filter and a high-pass filter used for obtaining bandpass characteristics for the receiving band. A switching device for changing the cut-off frequency of, at least, the low-pass filter is further provided for the high-frequency input circuit. The switching device is controlled to be on or off in response to the receiving frequency, thereby changing the passband of the high-frequency input circuit. Image disturbance characteristics can thus be improved.

Abstract: A display device has a time-constant circuit and a switching element such as a transistor for supplying the voltage of a battery to the time-constant circuit when a battery check key is pressed. A microcomputer measures a time interval from a time when the voltage of the battery starts being supplied to the time-constant circuit to a time when a voltage of the time-constant circuit reaches a predetermined value, and determines the remaining electric energy of the battery from the measured time interval. The microcomputer supplies data to a display unit which then displays a progressively variable display mark combination representative of the determined remaining electric energy of the battery.