Abstract A self-calibrating threshold detector for use with receivers adapted to receive an incoming transmitted signal carrying a prescribed code. The detector comprises a single demodulating channel which includes a mixer having one input receiving the incoming signal and another input receiving a local replica code. During a short time interval, an incorrect local code is applied to the mixer to incorrectly demodulate said incoming signal and to provide a reference level that calibrates the noise propagating through the channel. A sample-and-hold circuit is coupled to the channel for storing a sample of the reference level. During a relatively long time interval, the correct replica code provides an output level which ranges between the reference level and a maximum level that represents incoming signal presence and synchronism with the replica code. A summer subtracts the stored sample reference from said output level to provide a resultant difference signal indicative of the acquisition of the expected signal.
Inventors
👤 with respect to an invention of Frosch Robert A. Administrator of the National Aeronautics and Space Administration
In a system for receiving an incoming signal modulated by a prescribed code, the combination comprising: a. a correlator receiving said incoming code and successively cross-correlating same with a local replica of said incoming code and with an incorrect code, said correlator producing during one time interval a reference signal corresponding to the correlation with said incorrect code, and further producing during a successive time interval an output signal corresponding to the correlation with said replica code; b. hold means holding a sample of said reference signal; and c. comparator means comparing said sample reference signal with said output signal to provide a resultant difference signal indicative of said correlation with said replica code.
Claim 2
Dependent Claim
114 words
In a system for receiving an incoming signal modulated by a prescribed code, the combination comprising: a. a correlator receiving said incoming code and successively cross-correlating same with a local replica of said incoming code and with an incorrect code, said correlator producing during one time interval a reference signal corresponding to the correlation with said incorrect code, and further producing during a successive time interval an output signal corresponding to the correlation with said replica code; b. hold means holding a sample of said reference signal; and c. comparator means comparing said sample reference signal with said output signal to provide a resultant difference signal indicative of said correlation with said replica code.
Claim 3
Dependent Claim
14 words
The system according to claim 1 wherein said hold means is a sample-and-hold circuit.
Claim 4
Dependent Claim
38 words
The system according to claim 2 and further including: switching means for switching said replica code and said incorrect code to said correlator; and clock means for synchronizing the operation of said switching means and said sample-and-hold circuit.
Claim 5
Dependent Claim
37 words
The system according to claim 3 wherein said comparator means is a summer circuit and said clock means synchronize the application of said sample reference signal and said output signal to the two inputs of said summer.
Claim 6
Dependent Claim
57 words
The system according to claim 4 and further including: signal processing means comprising: a band-pass-filter coupled to the output of said correlator for extracting the correlated signals from adjoining signals; an amplitude detector for demodulating the correlated signals passed through said band-pass-filter; and amplifier means applying the output of said detector to one input of said summer.
Claim 7
Dependent Claim
19 words
The detector of claim 1 wherein said one time interval is relatively short compared to said successive time interval.