PRACTICAL RADIO RECEIVING SETS.'
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Two Interesting Instalments That Give Very Successful Results.
THE SUBJECT of the control of commercial vehicles by wireless has been fully. discussed in this journal, and we have shown that, given improvements in radio transmission and reception, the driver of a vehicle need never be out of touch with the offices of his controlling organization. It is, therefore, of interest herewith to describe two successful radio reception sets that are in daily use on automobiles, and which reproduce the transmissions of "2 L.O.," the London Broadcasting Station, within a range of 30 miles on load speakers. Using headphones, the range would be considerably more. A point that requires considerable emphasis in the first instance is the comparatively small length of aerial wire required to obtain these results.
The set shown on the Austin Twenty touring car was designed and made by Mr. Woodhams of the Park Motor Co., Jermyn Street, London. It consists of an aerial of copper strip, about 10 ft. long, slung between pores. The valve panel has accommodation for four valves, but in practice only two are used, one of these being the detector, 'before which is interposed one high-frequency amplifier. working on the popular tuned-anode rejector circuit, which is sa very simple and efficient coupling.
To transgress for a moment, it may here be mentioned that high-frequency amplification is very necessary if the length of the aerial is to be kept within reasonable limits. Moreoveri the tuned anode -circuit is very selective, and it would seem that it will become popular on all sets fitted to commercial vehicles, because it militates against interference of unwanted signals.
After the detector, the boosted and rectified current is taken to a power ampiffles consisting of two low-frequency valves in a separate case and working with, a high voltage on the plate circuit,
whence it is led to a Western electric loud speaker—a most efficient instrument.
The reproduction is so powerful that, when the ear was standing outside our offices, the broadcast concert could be heard distinctly through closed windows of rooms on the third floor. In the street it could be heard over 150 yards away. Such powerful reproduction would serve excellently to add to the attractions of motor coach picnicking. The other set has been fitted to a closed touring car by Mr. W. A. Appleton, designer to Radio Instruments, Ltd., of Hyde Street, Oxford Street, London. In this case, we have an extraordinarily compact circuit of seven valves, three working as high-frequency amplifiers and three as note magnifiers or L.F. amplifiers. The high-frequency coupling is by tuned transformers. Two Amplion loud speakers reproduce the actual broad
cast, the aerial is s single strand of wire neatly fitted round the inaide of the roof of the car, and the whole control is carried out by one snitch. One condenser knob suffices for all the tuning, which enables the set to be manipulated by the most inexperienced person. A set of this type would be very suitable for fitting to a closed motor coach or, with power-amplifiers, could be used in the open up to ranges of 40 miles. Duplicaters can be designed and supplied by Radio Instruments, Ltd.