Indianapolis Times, Volume 37, Number 122, Indianapolis, Marion County, 21 September 1925 — Page 33

ANNOUNCE CAUSES OF INTERFERENCE * Committee of National Electric Light Association Gives Out Compiled List —Eighteen Possibilities Found.

Causes of radio interference, according: to a list compiled by the radio committee of the National Electric Light Association, is as follows: Direct Current Arc Light Circuits The direct current arc type street lights ajre frequently the cause of disturbance to radio listeners. The most likely causes of interference from arc lights are grounds, loose connections and lamp jumping. The first two rarely occur and are easily found and fixed. Lamp jumping is generally due to one of the following three causes, and can be easily repaired: Broken or loose fitting globes, broken or loose flexible connection strip from upper electrode to upper electrode box, or broken flexible connection cable to movable clutch rod. Street lights Using Rectified Alternating Current Mercury-vapor tubes for rectifying alternating current for street lighting systems sometimes cause radio interference. The vacuum in these tubes; changes occasionally, and boiling in water restores the vacuum to the proper point. When these tubes are properly repaired, static disturbances are reduced to a minimum. Incandescent Street lighting Systems. In some cases the disturbance from Incandescent streelj lighting systems is audible several hundred feet, caused by static leakage across the porcelain base In the lamp itself. Replacement of the defective sockets with new ones eliminates the trouble. Elevator Controls Elevator motors and controls are the sources of a disturbance frequently difficult to remedy. Most of the disturbance originates in the contact in the elevator shaft, as the operator of the car moves the control handle back and forth. Sparking of the motor and control equipment also causes trouble. Thermostats Thermostats are now used to control dozens of different forms of devices ranging from large industrial undertakings to the furnace in the home. Thermostats sometimes cause disturbances, depending upon the size of the controls and the amount of current that they are handling. Condensers and radiofrequency choke coils properly placed will eliminate the disturbances. Heating Pads The make-and-break contact thermostat in some heating pads have caused trouble, which can be remedied by proper attention to -the design of the equipment. 7. Small Motors in the Home The sparking of the commutator in small motors is often a cause. Cleaning of these commutators and installing of new brushes from time to time, will reduce the disturbance. 8. Small Motors In Industry Small motors using direct-current are frequently sources of disturbance, covering limited areas, and usually confined to the place in which they are installed. Dirty and worn commutators and sparking brushes cause most of the disturbance in this type of motor. Connect a condenser across the motor leads, with the midpoint grounded. 9. Slip-King Alternating Current Motors The slip-ring alternating current motors are subject to heavy load, and also when pitting and corrosion of the slip ring occur, causing spcrking, radio disturbance is likely to occur. Proper repair and attention to the condition of the motor will eliminate much of this. 10. Battery Charging Devices. Vibrating, mecury-vapor, vacuum tube and other form of battery charging devices will interfere with radio reception for several hundred feet. Much of this trouble can be eliminated by the judicious use of condenser and chokes. 11. Electric Sign Flashers Electric sign flashers can effect radio reception for a considerable distance, depending upon the amount of current being consumed through the flasher. One case of this kind was eliminated by placing the flasher inside of a metal box, which was grounded. Trouble from this source has been observed as far as 800 feet. Precipitators and Treat ars Precipitators and treators usually employ rectified high voltage alternating current, obtained by means of a rotating gap. The voltage of this device ranges from 60,000 to 150,000. There are several types, the two primary groups being those for precipitating carbon particles from smoke, and for treating chemicals and mineral vapors In “treator” or precipitation tanks. These de-

vices sometimes cause trouble at a distance of fifteen miles from the source, depending upon the voltage and the arrangeraen* of the rotating gap. There is generally no difficulty in locating the source of such disturbances with a sensitive receiving set, equipped with a sharply directional loop. Disturbances can be minimized by insertion of a large radio-frequency choke coil between the gap and the bus bar, where many leads branch out to the separate treating operations. Flour Bleachers Some flour bleachers employ 50,000 volts, rectified alternating current. The disturbance may be heard over an area of ten square miles. The design of this device is similar to that of the precipitators. Gas Engine Ignitions The make-and-break system of ignition used on gas engines will usually set up a disturbance for several hundred feet. The usual method employed is to insert radio frequency chokes to correct this. Telegraph Offices Telegraph offices have been the source of disturbance for a block or so around, because of the constant making and breaking of circuits by keys and relays. Unless every key and every relay is furnished with a pair of condensers wtih the mid-point grounded, there does not seem to be much hope for eliminating this type of disturbance. I,arge Organs Each key on largo organs and each stop, is equipped with a small magnet, and as the organist runs over the keys $ contact is made and broken as he touches and releases the keys, in each case setting up a small disturbance representing sharp static. In view of the fact that there are 800 pairs of wires in such large organs this has been a difficult case to solve. Some progress has been made in eliminating this type of interference by inserting condensers and resistances in the main lead from the generator supplying the ten volt current for its operation. Telephone-Bell Ringers This is an intermittent interfer ence. Where the telephone exchange is located in the heart of the town, the constant ringing of the many bells forms a source of disurbance which seriously interferes with radio reception. The usual method employed to correct this interference, is to insert radio-frequency chokes in the leads. Street Railways % Radio interference is caused by faulty condition of tracks and overhead wires, and by defective rail bonds, and defective wheels or trolley poles of street railways which, becoming badly pitted and corroded, cause excessive sparking. Some relief may he obtained by draining the power circuit at a point beyond the parallel. The drain may consist of condensers connected between the power wires and the ground. Chokes in the power wires may be effective.

ENSEMBLE TO ENTER FIELD Stewart-Warner Corporation Plan New Set. A complete radio ensemble is planned by the Stewart-Warner Speedometer Corporation as its contribution to the radio industry. Known for more than twenty years as one of the world's leading manufacturers of automobile accessories, The Stewart-Warner Corporation now is planning to gain a name for itself as in the radio field. The ensemble consists of a reproducer especially designed to give harmony with Stewart-Warner radio instruments, radio tubes designed to operate at top efficiency, radio frequency amplification, a standard model radio set, with reproducer, a console table with built-in reproducer for use with two popular priced models, and two console model instruments with built-in reproducer and space for all necessary accessories. Stewart-Warner instruments are all five tube sets in which are incorporated the United States Navy circuit. The local branch of the Stewart-Warner Corporation, of which L. L. Banford is manager, Is supplying the dealers in this territory.

THE INDIANAPOLIS TIMES

Rheostat Plays an Important Part Much can be said about the humble rheostat that hides behind the front panel of receiving sets. Seldom seen and soon forgotten, this Important piece of apparatus opposes the flow of electricity to the filaments of the vacuum tubes while the set is in operation. Without a rheostat the filaments would soon become damaged beyond repair, due to too much current passing through and causing the thorium coating to disintegrate and flake off. This is an every-day occurence where the rheostats are turned on too far

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and is the principal reason for so many tubes going “dead.” In the struggle to oppose the flow of current the wire becomes warm, even hot, if the tube requires considerable “juice.” As the temperature of the rheostat rises it causis the wire to expand. If the wire becomes hot enough to char the insulation on which it is wound it becomes loose, the wires touch each other and the rheostate loses its smooth operation and trouble begins. It is for those reasons that the new F*rost rheostat has extra heavy wire on a strip of insulating material, the whole being In a molded bakelite frame. Heat will not, ruin the rheostat by changing the shape of the insulating

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