August 1955 | Other NBS Circular 557

Worldwide Radio Noise Levels Expected in the Frequency Band 10 Kilocycles to 100 Megacycles

William Q. Crichlow; D. F. Smith; R. N. Morton; W. R. Corliss

Abstract: External radio noise levels are presented in the form of an effective antenna noise figure Fa, which is defined as the noise power available from an equivalent lossless antenna relative to kt0b (the thermal noise power available from the passive resistance of a circuit with bandwidth, b, and at the standard absolute temperature, t0.) This form of expressing the noise has been chosen for convenience in combining for practical applications the noise received external to the antenna with the noise already present in the receiver. This form of presentation includes the frequency squared factor arising from the absorbing area of the receiving antenna and provides a measure of noise directly applicable to the “transmission-loss” method of measuring radio propagation.

Curves are given that show the expected median levels of radio noise during 4-hour time blocks for each season. The curves also show the effects of frequency and geographical location (using noise grade maps) and include atmospheric, galactic, and manmade noise sources.

The expected median values of atmospheric noise levels were largely based on the information given in the National Bureau of Standards Circular 462.

Also, the expected variability of noise levels within the 4-hour time blocks is given in terms of the ratios of the upper decile to medain [sic] level and median to lower decile level. These ratios are shown to be a function of frequency, time of day, and median noise-level amplitude.

The results of measurements at Boulder, Colo., Front Royal, Va., and Tatsfield, England, are shown in comparison with the expected levels.

Keywords: radio noise; man-made radio noise

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

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