Frequency Economy in Mobile Radio Bands

The various factors affecting the usability of mobile radio channels are discussed, and estimates are obtained for the number of usable channels per megacycle for several present and proposed methods of operation. The lack of radio-frequency selectivity is the principal barrier to maximum frequency economy, but this difficulty can be avoided by sufficient geographical and operational coordination. The increasing demand for all types of radio services emphasizes the need for efficient use of the radio frequency spectrum. In mobile radio operation the number of usable channels that can be obtained in the VHF and U H F mobile bands depends not only on the width of the individual channels, but also 011 how and where each channel is to be used. Activity 011 the same frequency at neighboring locations, and on neighboring frequencies at the same location both affect the usefulness of a channel. Halving the channel spacing doubles the number of potential assignments, but it does not double, and in some cases it does not appreciably increase the number of usable channels. The usefulness of a single isolated channel is determined by the intensity of its signal above the noise level. Because of the very wide variation in received signal strength caused by distance, terrain, building shadowing, etc., the coverage area of a channel can be discussed only in statistical terms. There are likely to be islands of poor signal-to-noise ratio even close to the transmitter, and the coverage gradually fades out into more spotty conditions at greater distance.