From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Guide on suppressing electrical interference for in-car radio reception and installing antennas.
| Identifier | ExFiles\Box 63\3\ scan0106 | |
| Date | 30th August 1934 guessed | |
| Ground the ignition coil housing, if ungrounded. Adjust and clean breaker points. Replace leaky or broken ignition wires. Adjust gaps in spark plugs. In some very stubborn cases with the ignition coil at or near the dash, away from the distributor and interruptor, the trouble can be remedied by relocating the coil at some point closer to both. Replace broken or otherwise defective suppressors. Bonding Besides filtering and shielding, it is sometimes necessary to resort to bonding; i.e., connecting to the motor and framework any and all parts that might pick up and radiate disturbances. The engine might be bonded to the frame. The steering column at its lower end to the motor-block. The shift lever and brake lever to the motor-block. Any rods or levers extending into the car from the motor compartment might be bonded to the motor. The bonding provides a path to ground of low resistance, thereby shorting out the induced interference currents. The material for bonding can be obtained in the form of a woven copper braid and is affixed by clamping under nuts and bolts or by soldering. Other Forms of Interference Body noise—Tighten all screws, nuts and bolts and bond all metal parts not already grounded. Brake static—Clean and adjust and bond all metal parts not already grounded. Another source of interference may be due to worn and sparking generator brushes and commutator. Resurfacing of the commutator and resetting of the brushes will end this disturbance. Be sure to use the generator condenser, however. It must be borne in mind that attempts to eliminate interference are of little use unless all parts of the antenna system are kept as far away as it is possible from the motor compartment. Keep the lead-in inside the car, shield it properly and bond it to the body of the car at several points along its length. Further information may be obtained when necessary by writing to the Service Department of this company, mentioning the year and model of the car, the model of the receiver and its serial number, also stating the position of set in car, location of antenna and nature of the trouble. Turn the set on; the dial will light up, and a very faint buzz may be noticed by placing a hand on the right side of the receiver case. This indicates that the vibrator is working. Wait about a minute for the tubes to heat up, then turn the left-hand control all the way to the right and tune in a station by turning the right-hand control. The frequency of the station in kilocycles can be read on the calibrated dial. Reduce the volume if desired by turning back the left-hand control. Now start the motor, while the set is playing, and listen for the motor noises in the receiver. You will notice the noises are greater as a station is tuned out. To the experienced radio mechanic, the amount of noise thus received will indicate whether or not the installation is a good one. Having tested the receiver with motor off and motor running, proceed as follows to suppress the motor noises. Shut off the engine. Attach one of the noise suppression condensers to the generator by slipping the mounting lug under a screw in the generator housing. See that the surface is clean and bright, (scrape it if necessary). To assure good electrical contact tighten the screw securely. Connect the live lead of the condenser to the cutout relay on the generator side. Attach the spark plug suppressors, one to each spark plug. See that each is screwed tightly—both to the plug and the lead. In like manner attach the distributor suppressor, supporting the wires to prevent them shaking loose due to vibration. These measures will be found adequate to suppress effectively all motor noise in the majority of cars and only occasionally will it be found necessary to resort to additional measures. Some suggestions covering these special cases are listed separately under “Service Instructions”. ANTENNA In order to obtain satisfactory reception, a good antenna must be provided. Because of the electrical disturbances created by the ignition system of an automobile, the pick-up of the antenna must be adequate to bring in the stations with sufficient strength, and the antenna should be in a position as far removed from the source of these disturbances as it is possible to place it. With these simple rules in mind and with a knowledge of the different antenna types, it should be comparatively easy to obtain efficient and trouble-free operation. Following is a brief discussion of accepted antenna types with suggestions for installing: 1. Roof antenna—Some cars are supplied by the manufacturers with a built-in roof antenna. This is recommended for the best results. The lead-in is usually to be found under the instrument panel. All that is required is to test for a possible ground, and to connect it according to the instructions given under the heading “Installation”. 2. Some cars that are not furnished with a built-in antenna are nevertheless equipped with a roof re-inforcement of wire netting which, although not originally intended for an antenna, may be used as such if ungrounded. Attach a shielded lead-in to one corner of the mesh. 3. On cars not having any such provision as the foregoing, an interior type of roof antenna may be employed with good results. One form of interior roof antenna may be a wire stretched back and forth and pinned to the lining of the top. Another form may consist of a strip of copper screening pinned to the top lining as before and extending along one side, across the back and along the other side forming a U, the lead-in being connected to one end. A special form of stick-on type of antenna may be used. 4. Keep an underslung antenna away from the distributor side of the motor and connect it to the receiver with a shielded lead-in, the shield being grounded securely at several points. | ||