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).
Methods for screening against wireless interference from sparking plugs when fitting a radio.
| Identifier | ExFiles\Box 163\2\ img013 | |
| Date | 17th November 1932 | |
| X6008 WST S/W. Hs{Lord Ernest Hives - Chair}/Wst...from PN.{Mr Northey} PN.{Mr Northey}5/WT17.11.32. Screening for Wireless. Again reverting to our conversation when I was at W. last, Messrs. Park Ward have an order for a 25 H.P. car from an American, and they have undertaken to fit it complete with a Roamer superhet radio instrument. I have already written to-day (PN.{Mr Northey}1/WT17.11.32) about this matter, and I informed Park Ward that we should object to having 50,000 ohms put in series with each of our sparking plugs. This has upset Park Wards considerably, as they state that this prospective owner finds it possible to have a wireless set on all high-class American cars in which the proposed screening is virtually the same, and we cannot of course take up the position of being the only motor manufacturers who object to screening. I have this morning had a long talk with the Engineer to the Philco Co. who appear to make a speciality of fitting radio sets to cars, and they have worked out a scheme of interference protection, which they state is acceptable and effective with all other makes of cars. It is also precisely the same method which they employed in fitting Sir Malcolm Campbell's car, and we certainly have not had any complaints from this owner as to the running of the car. I find that Philco put a 25,000 ohm carbon resistance in series with each plug, and also there is a 25,000 ohm similar type of resistance on the output from the coil secondary, which means that each plug has to function with an addition of 50,000 ohms in its circuit to what we would fit. Obviously we cannot turn down these schemes carelessly, but only after adequate inspection and experiment. Perhaps you have already made the necessary experiments, and can let me know whether and to what extent the method indicated above may be harmful, if at all. The matter is urgent, and I must deal with this in the case of Park Ward not later than Monday next. PN.{Mr Northey} | ||