In the method, a mixed signal is provided by mixing the tone signal with a reference signal alternating at a frequency fm between values related to sin fr and cos fr, where {HEAD ~ fr} is {TAIL ~ a frequency} substantially equal to fd and where fm is substantially greater than fr 
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In the method , a mixed signal is provided by mixing the tone signal with a reference signal alternating at a frequency fm between values related to sin fr and cos fr , where { HEAD ~ fr } is { TAIL ~ a frequency } substantially equal to fd and where fm is substantially greater than fr
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH