A second pair of signals is derived from {HEAD ~ the first pair} of {TAIL ~ signals} in which the second pair are displaced in phase relative to the first pair and are also in phase quadrature 
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A second pair of signals is derived from { HEAD ~ the first pair } of { TAIL ~ signals } in which the second pair are displaced in phase relative to the first pair and are also in phase quadrature
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH