Abstract :
An EMC Figure of Merit (FOM) for single-channel voice communications systems, based on the channel-denial concept, was developed by using a building-block approach. This approach assumes a co-site environment and involves the use of relatively simple scoring formulas for selected EMC parameters, which are linearly combined, with appropriate weighting factors, to calculate FOM´s for transmitters, receivers, and systems (i. e., transmitter-receiver pairs). The parameters chosen for transmitters included spurious emissions, noise near the carrier (i. e., broadband emissions outside the band containing desired modulation components), and intermodulation products. The parameters chosen for receivers were spurious responses, adjacent-signal interactions, and intermodulation products. The parameter scoring formulas were developed to reflect the frequency spectrum denied by each parameter. A channel was considered denied if (S+N+I)/ (N+I) < 10 dB in a moderately dense co-site environment. The weighting factors for the building-block approach were determined by running a computer program that kept track of the number of channels denied by each parameter. Example calculations for HF, VHF, and UHF systems are given, and the interpretation of the scores is discussed. The procedure developed enables quantification of the EMC characteristics of transmitting and receiving equipment. The EMC FOM provides system planners, design engineers and managers with a tool for making objective, consistent decisions. It also has potential value for those concerned with the formulation of EMC specifications and standards. It does not, however, indicate the absolute probability that compatibility will be obtained; rather, it gives information about the relative chance of obtaining compatibility.
