FM video data link spectrum spreading

摘要

A video data link system utilizes spread spectrum to decrease the susceptibility of a low power video link to radio frequency countermeasures. The video data link system utilizes a combination of spread spectrum direct-sequence modulation and frequency-hop along with frequency modulation to provide spectral spreading of radio frequency energy to a bandwidth much greater than the information bandwidth. The direct sequence modulation allows minimization of the number of frequency steps required for complete spectral filling of the operational bandwidth on an average basis. Frequency hop timing is determined from the phase of the direct sequence generator to simplify the frequency hop synchronization process in the receiver. Bandwidth of the fm video signal, after being spread in spectral width by the bi-phase direct sequence signal, is approximately equal to the direct pseudo random sequence clock rate. Spacing of the frequency hop step is matched to the direct sequence bandwidth to relate each frequency stepped subcarrier harmonically to the fundamental sequence clock, thereby allowing simpler generation of the de-hop sub-carriers in the receiver.