A wideband analog data link for the SEASAT-A synthetic aperture radar

A wideband analog data link has been developed by the Applied Physics Laboratory for NASA for transmitting both radar-return and timing-reference signals from the SEASAT-A synthetic aperture radar (SAR). The data link translates the 19-MHz signal spectrum of the SAR from 1275 MHz to the 2265-MHz downlink frequency. The radar timing signal is encoded by a pseudorandom noise code and overlaid on the downlink-signal spectrum. The data-link ground equipment consists of a SAR-unique demodulator coupled to existing NASA Spaceflight Tracking and Data Network (STDN) receivers. Significant features of the data link include preservation of signal coherency, realization of a linear 20-MHz analog channel, and time transfer of better than 1 ns.