pdq produces from the edge detector 47 an output that closes the contacts 46 to discharge the peak storage capacitor c4 thus the storage capacitor c4 is discharged at the beginning of each sweep cycle provided by the sweep signal swp each negative edge of the square wave signal pdq triggers the edge detector 47 to produce an output that places the circuit 48 in a sample mode to store the output of the peak detector 45 thus the output of the sample and hold circuit 48 is a signal proportional to v o and indicative of the peak voltages produced by the tank circuit 15 as illustrated by fig6 the specific composition of the output v o is dependent upon the load that is switched in parallel with the tank circuit 15 by the switching circuit 22 fig1 controlling the switching operation is the timing circuit 23 that provides timing signals shown in fig9 those signals include an antenna load timing signal a a low reference timing signal b and a high reference timing signal c all of which are applied to the switching circuit 22 in response to positive portions of the waveform a the switching circuit 22 closes switch contacts 16 to connect the antenna 19 in parallel with the tank circuit 15 similarly positive portions of the waveform b cause the switching circuit 22 to close the contacts 18 connecting the low reference impedance 21 in parallel with the tank circuit 15 while positive portions of the waveform c cause the switching circuit 22 to close the contacts 17.