Television Interference : Compulsory Suppression
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SUPPRESSORS have already been fitted to a number of commercial vehicles With petrol engines, notably to 25,000 Post Office vans and to London. buses not powered by compressionignition engines, but the Wireless and Telegraphy Bill, introduced by the Postmaster General, will make the use of these devices compulsory. It is expected that the operative date will be July 1.
A single resistor of 15,000 ohms in the distributor lead will probably be considered adequate to prevent the radiation of electrical discharges that interfere with the reception of television, which is the main objective. Various electrical concerns will be marketing simple devices for this purpose.
Belling and Lee, Ltd., Enfield, a pioneer in this field, has two available now. Type L 630, costing 2s., replaces the adaptor on the Lucas distributor casing, the lead from the coil being simply screwed into it. For Ford and other vehicles Type L 1274, costing
Is. 6d., is employed. The H.T. lead is cut and the ends pushed into a vulcanite sleeve resistor placed as near. to the distributor as possible.
If some enthusiastic inspector insisted upon more drastic measures, the suppression of the arc discharge from each plug might be required. For this purpose there is a simple attachment, Type L 1143, costing Is. 6d. per plug, which is interposed in a vertical or horizontal position between the H.T. lead and the terminal of the plug. This is the usual practice when installing radio in a motor vehicle. The plug suppressors should have a resistance of 5,000 ohms.
According to expert opinion, "it is doubtful whether electric vehicles of the battery-driven type would cause interference of a nuisance level, but no doubt the contactors and ancillary equipment could be suppressed with suitable condensers."
During spells of frosty weather, electric trains are bad offenders, but no solution would rppear to be possible.