Range Division Multiplexing.
DEPARTMENT OF THE NAVY WASHINGTON D C
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An apparatus is capable of recovering signals from N sites, N or 2, distributed along a single coaxial cable. This multiplexing technique allows the separation of signals from many transducers on one line. Time domain reflectometry TDR is used, with variable resistive elements distributed along the cable. TDR is used to detect discontinuities in the impedance of the cable as well as their specific location along the cable. The magnitude of these discontinuities is modulated by an impedance that is proportional to the applied signal. An excellent way of obtaining this kind of variable impedance along the line is to bias a field effect transistor FET so that it functions as a variable resistor. For a large number of signals to be multiplexed onto a coaxial cable, an FET is placed at each of the N signal sources. The coaxial cable has a characteristic impedance of Z sub 0 and the FETs are evenly spaced at a distance l. Each of the FETs produces a discontinuity on the cable that can be detected by using time domain reflectometry. Microphones may also be used instead of the FETs. Author
- Test Facilities, Equipment and Methods