A Long Term Trend in Urban Zone Man Made Radio Noise and the UHF Automotive Ignition Resonance

When the Urban Zone VHF/UHF band man made incidental radio noise power data are separated into two sets, namely that obtained before 1970 and after 1975, a distinct demarcation is observed. The data of recent acquisition in the frequency range 80 MHz to 950 MHz are seen to lie 10 or more decibels below the older data. The circumstantial evidence avail­ able suggests a decrease in automotive ignition system noise occurred to which this the Urban Zone level change may be attributed. Revealed by this grouping of the Urban Zone data is the third automotive ignition noise resonance lying between 150 MHz and 500 MHz. The resonance is sufficiently resolved from the background that it has been possible to fit a single pole function to the observations by the method that yields antenna noise figure F as a function of a frequency for the interval 100 MHz to 1 GHz.