SHORT-WAVE RECEPTION

Radio Record, Volume I, Issue 30, 10 February 1928, Page 3

SHORT-WAVE RECEPTION

NEW VALVE PROMISES WONDERS. Important developments in the construction of short-wave receivers are likely to be one outcome of the invention of the new English shielded plate receiving valye which was mentioned recently in these columns. The main effect of the shield is to reduce the capacity of the valve almost completely. In the ordinary valve the capacity between the plate and the grid is comparatively great, and the valve really resembles a small condenser. The effect of this, if the valve is used as a high-frequency amplifier for very short waves, is that the capacity of the valve acts as an almost complete short-circuit in the valve itself, to au incoming signal impulse. The consequence is that an incoming signal passes right across the valve without being amplified, and no gain is obtained in the high-fre-quency amplifying valve. This effect has hampered the construction of a short-wave receiver itcorporating @ high-frequency amplifier. TO ADD RADIO FREQUENCY. The new screened valve, however, will overcome this weakness of the ordinary valve, and its influence may ultimately be greatly to increase the scope of short-wave broadcasting. At present the real value of short-wave broadcasting is partially limited to the transmission of programmes from one couttry to another for rebroadcasting. The majority of listeners hear the programme after it is relayed, instead of picking it up direct from the cverseas station. ~It is likely, however, that the use of screened valves in high-fre-quency amplifiers will result in the production of a simply operated short-wave receiver, which will give ‘fairly cousistent loudspeaker reception from short-wave stations in all parts of the world. ‘Ie yalue of this will be that the listener will be able to tune-in whatever overseas station he likes.