The transmitter in this experiment used an LCR with a 2" square front face, and was made with commercial bus driver chips. We expect less ringing in the antenna signal when we repeat these experiments with our own transmit antenna drivers (i.e. nstest11). The receiver consisted of a Close-Loop Sensor feeding a broadband differential input amplifier. The transmitter generated a synchronization pulse for triggering the digital storage oscilloscope over a fiber optic link. Since the transmitter was also battery powered, no conduction path existed between transmitter and receiver.
In both Figures 17 and 18, the ensemble averaged waveforms are plotted together with the vertical position corresponding to the separation of the transmit and receive antennas. In Figure 17, the amplitudes are normalized, and in Figure 18, the relative amplitudes are preserved. These plots show the evolution of the received signal with both time and distance. The wavefront is progressively delayed with increasing distance, but also note the changing shape. At close range, the signal reflects the waveform of the current through the LCR, which was a square wave with some ringing. As the receiver is moved out of the near field of the transmitter, the received signal becomes proportional to the derivative of the current through the LCR, (i.e. the body of the square wave disappears).
FIGURE 17. Digitized Oscilloscope traces of Impulse streams received at distances of 2 feet thru 30 feet in 2 foot increments, with their amplitudes normalized. Their placement in the graph is proportional to the range. The waveforms have been box-averaged with a 500 ps period. The impulses were transmitted in doublet pairs (+impulse followed by a -impulse 13 ns later) with a doublet separation of 20 ns. The scope traces were synchronized via a trigger delivered by fiber optic cable, with up to 1023 traces internally averaged by the scope.
FIGURE 18. Digitized Oscilloscope traces of Impulse streams received at distances of 2 feet thru 30 feet in 2 foot increments, with their relative amplitudes preserved to show the reduction in signal strength with range. The bottom trace is a baseline measurement with the transmitter turned off, showing the noise in the reception apparatus. Other than the baseline, the trace placement in the graph is proportional to the range. The waveform data are the same as in Figure 17.
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