(under subclass 391) Subject matter wherein the bandwidth reduction is performed by folding the higher frequencies down to fit inside a reduced frequency spectrum by sampling at a rate less than twice the highest frequency, causing the alias and baseband spectrums to overlap.
(1) Note. The Nyquist criteria states that the sampling rate should be at least twice the baseband. In sub-Nyquist systems, the sampling rate is less than the required Nyquist sampling rate.
(2) Note. The alias components, which are generated by sampling and centered on the sampling frequency, are normally placed in teeth or gaps of the video spectrum to allow
recovery of the original full band signal.
(3) Note. These systems often use comb filters (2 or 3 dimensional filters using line, field, or frame delays) to remove any signal in the gaps.
