An Orthogonal Detection Kit to Suppress Common-Channel Interference

A new technique named "rthogonal detection" which suppresses common-channel double sideband interference has been investigated in detail. It is applicable to various types of reception systems without materially affecting the desired signal for most interference situations. To illustrate the principles involved, a modification kit was developed to suppress double sideband interference into a high-frequency SSB communications receiver. It appeared that for certain idealized situations the double sideband interference could be suppressed almost completely. Practical considerations, however, limited the suppression of the unwanted signal to something in the order of 30 db. The amount of suppression was shown to be equal to both a constant and a variable improvement factor. The variable factor converts a negative decibel signal-to-interference ratio into a positive decibel signal-to-interference ratio improvement. Thus, for certain conditions, the weaker the desired signal the greater will be the suppression of the interference. The technique for certain situations is also capable of separating both pulse or CW common-channel waveforms which are simultaneously amplitude and phase modulated. In addition to offering major advantages over other approaches that eliminate common-channel interference, the technique is applicable to suppressing strong adjacent channel in interference.