a bi - static radar configuration measures the direct time - of - flight of a transmitted rf pulse and is capable of measuring this time - of - flight with a jitter on the order of about one pico - second , or about 0 . 01 inch of free space distance for an electromagnetic pulse over a range of about one to ten feet . a transmitter transmits a sequence of electromagnetic pulses in response to a transmit timing signal , and a receiver samples the sequence of electromagnetic pulses with controlled timing in response to a receive timing signal , and generates a sample signal in response to the samples . a timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver . the receive timing signal causes the receiver to sample the sequence of electromagnetic pulses such that the time between transmission of pulses in the sequence and sampling by the receiver sweeps over a range of delays . the receive timing signal sweeps over the range of delays in a sweep cycle such that pulses in the sequence are sampled at the pulse repetition rate , and with different delays in the range of delays to produce a sample signal representing magnitude of a received pulse in equivalent time . automatic gain control circuitry in the receiver controls the magnitude of the equivalent time sample signal . a signal processor analyzes the sample signal to indicate the time - of - flight of the electromagnetic pulses in the sequence . the sample signal in equivalent time is passed through an envelope detection circuit , formed of an absolute value circuit followed by a low pass filter , to convert the sample signal to a unipolar signal to eliminate effects of antenna misorientation .