Load Rating Theory for Multi-Channel Amplifiers

I N A perfect multi-channel carrier telephone system, each channel would be entirely free from interference produced by the energy present in the other channels. Since all the channels are amplified by the same repeaters, which as a practical matter cannot have perfectly linear characteristics, this is an ideal that may be approached but not completely realized. The interchannel interference must be kept down to a value which will be satisfactory for the grade of transmission concerned, further reduction being uneconomic. To do this the repeaters must meet definite load capacity requirements and modulation (non-linearity) requirements. The load capacity requirement is most conveniently specified in terms of the maximum single frequency sine wave power which a multi-channel amplifier must transmit without appreciable overloading. The modulation requirement pertains to the performance of the amplifier for impressed loads equal to or smaller than the load capacity, and specifies the allowable power in the modulation products resulting from such loads. Because of the numerous factors which affect these requirements, their determination is a rather complicated matter and the present discussion will be restricted solely to a determination of the load capacity requirement. The object is to determine this quantity as a function of N, the number of channels in the system. The criteria ordinarily used for determining the load capacity of single-channel amplifiers are of little use here because of two funda-