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9-1: Basic Principles of Signal Reproduction
Selectivity: Shape Factor
The sides of a tuned circuit response curve are known as skirts.
The steepness of the skirts, or the skirt selectivity, of a receiver is expressed as the shape factor, the ratio of the 60-dB down bandwidth to the 6-dB down bandwidth.
The lower the shape factor, the steeper the skirts and the better the selectivity.