A Video Recorder for Coherent Doppler Radar

A system for recording coherent pulse Doppler radar signals on an inexpensive video tape recorder is described. A recording processor translates the radar receiver IF output to a center frequency of 1 MHz. To this is added an amplitude modulated 200-kHz pilot carrier. This unique pilot carrier provides a coherent reference for synchronous demodulation, a timing reference, and synchronization signals for the video tape recorder. A reproducing processor reconstructs the original radar signals from the information contained in the reproduced tape through the use of a pilot tracking loop, which recovers the synchronous reference in the presence of added noise and tape recorder flutter. An analysis of system performance characteristics is included. Of note is the good definition of the start time of the radar interval. Maximum timing jitter at the end of the 1-ms radar interval is about 400-ns peak, and is under 10 ns for the first 10 μs of the interval. The linear dynamic range of 27 dB can be used to provide about 4-dB resolution over a 90-dB dynamic range using a log compression technique to be discussed. Comparisons between radar signals measured directly and signals recorded on the radar video recorder indicate that velocity information present in a coherent Doppler radar is preserved with high accuracy.