The Use of Holbrook and Dixon Loading Factors in Setting Receiver Parameters for an FDM-FM Radio Telephone Communication System

It is convenient to use a 0-dBm sinusoidal test tone to set the deviation of an FM radio transmitter. It is of interest to know the peak frequency deviation produced by the composite talker signal, relative to the deviation assigned to the 0-dBm test tone. This is necessary to design the equipment with the proper RF bandwidth. If the RF bandwidth is too small, the system will be overloaded and distortion will be produced. If the RF bandwidth is too wide the receiver noise level will be increased. This will cause an unnecessary increase to the amount of time below threshold. The Holbrook and Dixon load factors allow for a practical receiver design, the utilization of which is demonstrated by an illustrative problem. In a particular example the 1.0-Mc/s bandwidth is the limiting parameter and this determines the design value of the test tone frequency deviation. In another system the limiting parameter may be a minimum value for the carrier-to-noise ratio or the voice channel SNR. The inter-relationship of the various receiver parameters is demonstrated here, and design procedures can be evolved from it for any specific requirements.