Special Interference

Radio Record, Volume I, Issue 25, 6 January 1928, Page 12

Special Interference

HOW TO SUPPRESS THE TROUBLE

The radius of interference from picture theatres is usually up to 200 yards, the direct-current generator employed being the cause of the trouble It would be supposed by most peopk that the are lights in use would pro duce interference, but such is not the case. More interference will usually be experienced trom the generator before the are is "struck," than when it is in use.’ ‘To remedy such generator interference, a suitable fixed condenser of 2 mfds capacity is connected by a 5-amp fuse to each brush, the other ‘side of each condenser being connected to earth or to the bed of the machine. If the commutator is worn, it should be turned down in a lathe, The quality of the carbon brushes used has an effect upon interference. STREET LIGHTING. Arc lamps themselves do not produce interference, but leakages on the circuit can cause a great deal, owing to the comparatively large amount of current handled. Interference can be produced by rectifying tubes at the central station. Incandescent street lamps produce a great more interference than do the arc lamps. This is not due to eny

difference in the actual system, but to less careful installation, and the condition is general. he most frequent causes of interfering noise are leakages caused by rain or moisture, loose conuections of wires at lamps, lamps loose in their sockets, defective insulators, etc. Such interference is difficult to locate, and of course remedy rests with the authority concerned. FACTORY BELTS. Iriction between pulleys and belting will set up sufficient static sparking to be heard in a nearby receiver. It has been demonstrated that the film of oil in the bearings is sufficient to prevent this electric charge from. immediately sparking to earth through the frame of the machine. ELECTRIC WARMING PADS. These are fitted with smal! thermostats that automatically switch the current on atid off to keep the heat uniform, causing annoying clicks in a receiver either in the same house or the one on either side. Corroded or burned contacts often accentuate the trouble, but if cleaning them does not sufficiently reduce interference, a condenser may be put across the leadswith a fuse.