Overcoming Radio Interference by Trolley-buses
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SOME complaints have been made in the past by radio listeners regarding the interference to their reception caused by trolley-buses and trams. To overcome this trouble the English Electric Co., Ltd., Preston, has designed special choke coils for the purpose of eliminating interference to radio transmission on short and medium wave-lengths.
These ooils' two in number, are mounted on the roof of each bus, and are connected in the circuit of the two trolley
arms. The weight of the• coils is very small, being only 34 lb., and that of their easing, either cast aluminium or wood, 17i lb., giving a total weight for the complete apparatus of 51i lb.
It may be recalled that, in order to achieve the ultimate removal of this cause of interference, the Tramway and Trolley Bus Broadcast Interference Committee was set tip in April, 1931, at the instigation of the Post Office. From the outset the Post Office placed the services of its expert staff and testing equipment at the disposal of the committee for investigation work, the transport and manufacturing undertakings providing all other facilities. The introduction of these coils is the outcome of the work of this committee. Following the introduction of a fleet of 60 trolley-buses on the Kingston-Twickenham route of the London United Tramways in May, 1931, numerous complaints were received from broadcast listeners, and the tramway company appealed to the committee to find some remedy. Eliminator coils mannfactureby the English Electric Co., Ltd., were fitted to the A.E.C.-English Electric trolley-buses, which, incidentally, were the first vehicles of this type to operate in the London area.
Exhaustive tests showed that the use of these coils reduced acute interference almost to the point where it was barely perceptible, even when -six trolley-buses were passing at the same time the place where the test radio set was in operation.