Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Patent
1987-12-21
1990-05-22
Safourek, Benedict V.
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
455303, 455305, 455296, 328167, 307526, 307520, H04B 110, H04B 112
Patent
active
049283154
ABSTRACT:
A chirped backscatter filter 10 compares a received signal (RSIG) to a reference signal related to a transmitted signal (TSIG) and removes from RSIG the frequency component which is equal to TSIG in frequency. This removed frequency component corresponds to the frequency of the transmitter backscatter radiation. The filter of the invention adds a frequency offset (f.sub.n) to both RSIG and TSIG in mixers 12 and 14 before substracting one from the other in mixer 22. Thus, equal frequency components in both RSIG and TSIG, such as the backscatter radiation frequency component of RSIG, will equal f.sub.n. The frequencies resulting from this subtraction are thereafter passed through a notch filter 24 which is centered on f.sub.n and which passes all frequency components except f.sub.n. The output of the notch filter thus no longer has a frequency component associated with the backscatter frequency component. The loss of the RSIG phase reference due to the phase reference between the RSIG and TSIG modulation envelopes being destroyed during the backscatter filtering process is therafter compensated for by adding TSIG to the filtered difference frequency component, thereby reestablishing the phase relationship of the original RSIG frequency components minus the backscatter frequency component.
REFERENCES:
patent: 3744015 (1973-07-01), Marimon et al.
patent: 4067013 (1978-01-01), Smith
patent: 4177430 (1979-12-01), Paul
patent: 4569072 (1986-02-01), Van Roermund
patent: 4731587 (1988-03-01), Jensen
Arnn Edward L.
Jensen Preben B.
Denson-Low Wanda K.
Hughes Aircraft Company
Safourek Benedict V.
Smith Ralph
Streeeter William J.
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