FM video data link spectrum spreading
First Claim
1. In a communications system video data link for transmitting video information from a first point to a second point where signals are subsequently received, said data link having a video source signal that is frequency modulated prior to transmission and said received signals are received, discriminated, recorded, and monitored;
- the improvement comprising the method of transmitter-receiver synchronization to achieve spectrum spreading;
generating a time code onto a video source baseband signal prior to frequency modulation and transmission of said signal from a transmitter;
generating a direct sequence code at a preset high frequency clock rate;
mixing the direct sequence code with the transmitted, time coded, frequency modulated, video signal to obtain a spread spectrum signal output; and
amplifying said spread spectrum signal and transmitting said signal from an antenna.
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Accused Products
Abstract
A video data link system utilizes spread spectrum to decrease the susceptlity 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.
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Citations
11 Claims
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1. In a communications system video data link for transmitting video information from a first point to a second point where signals are subsequently received, said data link having a video source signal that is frequency modulated prior to transmission and said received signals are received, discriminated, recorded, and monitored;
- the improvement comprising the method of transmitter-receiver synchronization to achieve spectrum spreading;
generating a time code onto a video source baseband signal prior to frequency modulation and transmission of said signal from a transmitter; generating a direct sequence code at a preset high frequency clock rate; mixing the direct sequence code with the transmitted, time coded, frequency modulated, video signal to obtain a spread spectrum signal output; and amplifying said spread spectrum signal and transmitting said signal from an antenna. - View Dependent Claims (2, 3)
- the improvement comprising the method of transmitter-receiver synchronization to achieve spectrum spreading;
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4. In a communications system video data link wherein a plurality of radio frequency signals are transmitted and subsequently received, said data link having a video source signal that is frequency modulated prior to transmission and said received signals are received, discriminated, recorded, and monitored;
- the improvement comprising the method of transmitter-receiver synchronization to achieve spectrum spreading;
frequency modulating and transmitting a time coded baseband video signal from a video source; generating a PN code at a preset mid-frequency clock rate; coupling said generated PN code to respective first and second mixers; driving in sequential steps a programmable frequency synthesizer to provide first and second output signals along signal paths shifted in phase by 90 degrees and stepped in equal mid-frequency steps in a pseudo random pattern; directing output signals from said synthesizer along said first and second output signal paths to said first and second mixers respectively for obtaining respective first and second frequency-hopped, PN coded outputs therefrom; combining said first and second frequency-hopped PN coded outputs respectively, along separate and distinct signal paths, with said frequency modulated time coded baseband video signal; summing the respective combinations of frequency-hopped, PN coded outputs with the frequency modulated and time coded baseband video signals to provide an output spectrum of hopped PN coded signals; and amplifying and transmitting said spectrum of hopped PN coded signals toward a receiver region. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11)
- the improvement comprising the method of transmitter-receiver synchronization to achieve spectrum spreading;
Specification