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).
The effect of a suppressor in the coil H.T. lead on radio interference from a car ignition system.
| Identifier | ExFiles\Box 168b\1\ img176 | |
| Date | 29th March 1939 | |
| Lr{Mr Ellor}/HWS/SGL.1/WJ.29.3.39. RADIO INTERFERENCE FROM CAR IGNITION SYSTEM. EFFECT OF SUPPRESSOR IN COIL H.T. LEAD. Measurements of the interference have been carried out to show the effect of a single suppressor fitted in the coil H.T. lead. METHOD OF MEASUREMENT. The output from a Marconi radio receiver was connected to a cathode ray oscillograph and the resulting waveform photographed. The oscillograms produced show the rectified waveform of the disturbance, and the height of this waveform is proportional to its field strength. The measurements were only comparative, since the absolute value of the field strength cannot be found without a calibrated field strength measurement set. The photographs were taken with the car engine running light at 2000 RPM. about 12 yds. from the receiver. EXPERIMENTAL RESULTS. Photographs 1 to 3 show the effect with the receiver tuned to the wavelength of the London television transmitter. The screen over the plugs reduces the interference by 30% and the suppressor (10,000 ohms) reduces it by at least 90%. A 5000 ohm suppressor produces almost exactly the same reduction as the 10,000 ohm one. Photographs 4 to 6 show the effect at a medium wavelength 350 metres. The sensitivity of the apparatus was adjusted to be 6 times that value used for the television wavelength. It can be seen that the interference at this wavelength (without the suppressor) is about 1/6 of that at the television wavelength, and that with the suppressor fitted it is only just visible above the background. No sound due to the interference was audible when the speaker was switched on. It appears therefore, that the interference is reduced sufficiently both at 'television' and at 'broadcast' wave-lengths. Lr{Mr Ellor}/HWS/S.G.Lankester. | ||