A Compact Loud Speaker on an 11.9 h.p. Bean.
One result of the growing interest in wireless telephony is that motorists are beginning to equip their vehicles with various forms of receiving instruments, and we have lately observed quite a number of sporting cars so equipped. Taken in general, the ordinary form of receiving set has many disadvantages when applied to cars. For one thing, the space occupied is apt to impede the passengers, and the usual arrangement of the component parts is not altogether desirable. A very good solution to the problem of fitting cars up with wireless has been reached by one of the comin the in the recent M.C.C. London-toEdinburgh run, and was demonstrated to good effect in Wroth am Park, Barnet, whilst he was waiting Ins turn to start. The car in question is a standard 11.9 Bean four-seater, and the
whole of th-s equipment i absolutely self contained, though it can be used with equal success apart from the car by having a spare accumulator. The set is known as the R. T. 13, and
has been specially designed for the purpose by Captain Richard Twelvetrees. It embodies three valves and a crystal detector. A small frame aerial is mounted, when required, on one corner of the wind screen, and the high tension battery is fixed beneath the set, . which occupies a space on the dashboard. Special leads from the car lighting set provide the current for the valve filaments, all the leads having Plug-in terminals, which fix into clips when not in use. The circuit consists of one high frequency valve, one dual valve amplifying both high and low frequency impulses, and one low frequency valve or note magnifier. The high frequency impulses of the broadcast wave are rectified by means of a special combination of crystals, ,after being amplified by the first and second valves. rhe circuit includes two tuned anodes on the high frequency side, ordinary transformers being employed f?r the low frequency. Two Polar condensers and one air-dielectric condenser are used for tuning to the • required wave lengths, which operate in conjunction
with a three-way variable coil holder with vernier adjustment. The overall dimensions of the set mounted on the dashboard are 12 in. by Io in. by 4 in., one reason making so small a space possible being the adoption of the Fuller type of rheostats for regulating the current to the valve filaments. A four pole rotary double throw switch permits of the current from batteries being turned on and off at will, so that no waste of current is possible when the set is not in use. The illustration reproduced herewith shows the general lay-out
of the instrument, which in no way interferes with the leg room of the passenger in the front seat. Though reception whilst the cans in motion is quite possible with the form of aerial illustrated, further experiments are in progress with a type of aerial which will be absolutely nondirectional, so that no fading will take place as the cans deflected out of its course during a run. Some little interference has been experienced from the
electrical disturbance created by the magneto when the engine is running, but this is not enough to spoil the quality of tone from the loud speaker. It is an easy matter, however, to arrange for the screening of the plugs, high tension leads and magneto after the manner adopted in aeroplane engines.
On. the return from the Edinburgh run, a series of tests were carried out, the most notable being that of receiving the Newcastle programme on Sunday afternoon, with a frame aerial at a distance of fifty miles from the station in the pouring rain. It was found quite easy to tune in the set to give a clear loud speaker strength. When the car is stationary and a piece of covered wire is thrown over any convenient tree to give an aerial length of about forty feet, and a suitable earth, one can travel all over England without losing touch with a broadcasting station, with the possible exception of localities notorious amongst wireless experts as being “blind spots.”