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