Radio receiver with automatic interference cancellation

In a radio receiver for receiving desired signals in a predetermined frequency band and having means for eliminating a particular narrow frequency band of received signals among the desired signals in an electrical path in the receiver that has an input and an output, the improvement comprising,

• (a) a passive variable narrow band pass filter, tunable to the frequency of said undesired narrow band having an input and an output,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) a phase reversing amplifier for receiving said passive filter output producing phase reversed signals,
• (d) means for combining said phase reversed signals with said electrical path output, producing a combined signal output,
• (e) said receiver electrical path input, said means for sampling, said passive filter and said phase reversing amplifier being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said receiver electrical path being coupled electrically in parallel with the output of each coupled to said means for combining and
• (e) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said combined signal output.

In a radio receiver for receiving desired signals in a predetermined frequency band and having means for eliminating a particular narrow frequency band of received signals among the desired signals in an electrical path in the receiver that has an input and an output, the improvement comprising,

• (a) a passive variable narrow band pass filter, tunable to the frequency of said undesired narrow band having an input and an output, the resistive impedance of said pass filter having R1,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) a phase reversing amplifier for receiving said passive filter output producing phase reversed signals, the feedback impedance of said phase reversing amplifier being R3, whereby the gain of said phase reversing amplifier is R3/R1,
• (d) a summing amplifier for combining said phase reversed signals with said electrical path output, producing a combined signal output and
• (e) said receiver electrical path input, said means for sampling, said passive filter and said phase reversing amplifies being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said receiver electrical path being coupled electrically in parallel with the output of each coupled to said means for combining and
• (g) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said combined signal output.

In a radio receiver for receiving desired signals in a predetermined frequency band and having means for eliminating a particular narrow frequency band of received signals among the desired signals in an electrical path in the receiver that has an input and an output, the improvement comprising,

• (a) a passive variable narrow band pass filter having resistive impedance and reactive impedance, tunable to the frequency of said undesired narrow band and having an input and an output, said resistive impedance of said passive filter being R1,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input, (c) a phase reversing amplifier for receiving said passive filter output producing phase reversed signals, the feedback impedance of said phase reversing amplifier being R3, whereby the gain of said phase reversing amplifier is R3/R1,
• (d) a summing amplifier for combining said phase reversed signals with said electrical path output, producing a combined signal output,
• (e) said receiver electrical path input, said means for sampling, said passive filter and said phase reversing amplifier being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said receiver electrical path being coupled electrically in parallel with the output of each coupled to said means for combining and
• (g) the resistive impedance between said electrical path output and said summing amplifier being R4,
• (h) the resistive impedance between the output of said phase reversing amplifier and said summing amplifier being R5,
• (i) said passive filter is varied by varying said reactive impedance thereof and
• (j) R3/R1 and R4 and R5 are such that the undesired signals are substantially eliminated from the received signals in said combined signal output.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band, means for reducing the effects of undesired rceived signals among the beacon signals in an electrical path having an input and an output in the Loran receiver comprising,

• (a) a passive variable narrow band pass filter, tunable to the frequency of said undesired narrow band having an input and an output,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) means for reversing phase of the signals of said sample that reach the output of said passive filter,
• (d) means for combining said phase reversed signals with said electrical path output, producing a combined signal output and
• (e) said Loran receiver electrical path input, said means for sampling, said passive filter and said means for reversing phase being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said Loran receiver electrical path being coupled electrically in parallel with the output of each coupled to said means for combining and
• (g) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said combined signal output.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band, means for reducing the effects of undesired received signals among the beacon signals in an electrical path having an input and an output in the Loran receiver comprising,

• (a) a passive variable narrow band pass filter, tunable to the frequency of said undesired narrow band having an input and an output,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) a phase reversing amplifier for receiving said passive filter output producing phase reversed signals,
• (d) means for combining said phase reversed signals with said electrical path output, producing a combined signal output and
• (e) said Loran receiver electrical path input, said means for sampling, said passive filter and said means for reversing phase being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said Loran receiver electrical path being coupled electrically in parallel with the output of each coupled to said means for combining and
• (g) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said combined signal output.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band, means for reducing the effects of undesired received signals among the beacon signals in an electrical path having an input and an outputin the Loran receiver comprising,

• (a) a passive variable narrow band pass filter, tunable to the frequency of said undesired narrow band having an input and an output, the resistive impedance of said passive filter having R1,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) a phase reversing amplifier for receiving said passive filter output producing phase reversed signals, the feedback impedance of said phase reversing amplifier being R3, whereby the gain of said phase reversing amplifier is R3/R1,
• (d) a summing amplifier for combining said phase reversed signals with said electrical path output, producing a combined signal output and
• (e) said Loran receiver electrical path input, said means for sampling, said passive filter and said phase reversing amplifier being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said Loran receiver electrical path being coupled electrically in parallel with the output of each coupled to said summing amplifier and
• (g) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said combined signal output.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band, means for reducing the effects of undesired received signals among the beacon signals in an electrical path having an input and an output in the Loran receiver comprising,

• (a) a passive variable narrow band pass filter having resistive impedance and reactive impedance, tunable to the frequency of said undesired narrow band and having an input and an output, said resistive impedance of said passive filter being R1,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) a phase reversing amplifier for receiving said passive filter output producing phase reversed signals, the feedback impedance of said phase reversing amplifier being R3, whereby the gain of said phase reversing amplifier is R3/R1,
• (d) a summing amplifier for combining said phase reversed signals with said electrical path output, producing a combined signal output,
• (e) siad Loran receiver electrical path input, said means for sampling, said passive filter and said phase reversing amplifier being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said Loran receiver electrical path being coupled electrically in parallel with the output of each coupled to said summing amplifier and
• (g) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said combined signal output.
• (h) the resistive impedance between said electrical path output and said summing amplifier being R4,
• (i) the resistive impedance between the output of said phase reversing amplifier and said summing amplifier being R5,
• (j) said passive filter is varied by varying said reactive impedance thereof and
• (k) R3/R1 and R4 and R5 are such that the undesired signals are substantially eliminated from the received signals in said combined signal output.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band, the method of reducing undesired received signals among the beacon signals in an electrical path in the Loran receiver including the steps of:

• (a) detecting the presence of the undesired signals among the received beacon signals in the electrical path in the Loran receiver and producing an output representative of the frequency of detected undesired signals,
• (b) sampling the undesired received signals with a passive variable narrow band pass filter of band width substantially less that the frequency band containing the beacon signals, in said electrical path in the Loran receiver, and
• (c) reversing the phase of the undesired received signals from the output of said passive filter and
• (d) combining said reversed phase signals with said received signals in the electrical path and
• (e) varying said passive filter to insure that said undesired signals are substantially cancelled in said electrical path in the Loran receiver.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band and having an RF section with means for reducing the effects of undesired received signals among the beacon signals in a portion of the frequency band of said received signals including a variable narrow band pass filter that is tunable to different narrow bands of frequency in said portion of the frequency band of said received signals and means for sampling said received signals and feeding said sample to said variable narrow band said pass filter input, means for identifying the maximum undesired received signal among said undesired received signals and tuning said variable narrow band pass filter to said identified maximum undesired received signals, comprising,

• (a) means for generating variable narrow band pass filter frequency control signals,
• (b) means for applying said control signals sequentially to said variable narrow band pass filter,
• (c) whereby said said variable narrow band pass filter is sequentially tuned to successive narrow frequency bands across said portion of the frequency band of said received signals and produces an output signal that corresponds to one of said control signals,
• (d) means for comparing the present magnitude of the output of said variable narrow band pass filter at each of said sequential tunings with the magnitude of the output of said variable narrow band pass filter at a previous of said sequential tunings,
• (e) means responsive to said comprising means for storing said control signal that corresponds to said present output when said present output magnitude exceeds said previous output magnitude and
• (f) means for applying said stored control signal to said variable narrow band pass filter.

In a Loran receiver for receiving Loran beacon signals in a predetermined frequency band and having an RF section with means for reducing the effects of undesired received signals among the beacon signals in a portion of the frequency band of said received signals including two variable narrow band pass filters that are each tunable to the same different narrow bands of frequency in said portion of the frequency band of said received signals and means for sampling said received signals and feeding said sample to each of said variable narrow band said pass filter inputs, means for identifying said undesired received signal among said undesired received signals and sequentially tuning first one and then the other of said variable narrow band pass filters to different of said identified undesired received signals, comprising,

• (a) means for generating variable narrow band pass filter frequency control signals,
• (b) means for applying said control signals sequentially first to one of said variable narrow band pass filters and then to the other,
• (c) whereby first said one variable narrow band pass filter is sequentially tuned to successive narrow frequency bands across said portion of the frequency band of said received signals and produces an output signal that corresponds to one of said control signals and then the other of said variable narrow band pass filter is sequentially tuned to successive narrow frequency bands across said portion of the frequency band of said received signals and produces an output signal that corresponds to one of said control signals,
• (d) means for storing said control signal for said one variable narrow band pass filters following said successive tuning thereof,
• (e) means for comparing said stored control signal with said control signals successively applied to said other variable narrow band pass filter and
• (f) means responsive thereto for eliminating from among said successively applied control signals those that are the same as said stored control signal.

A narrow band pass notch filter centered at a radio frequency F in an electrical path for radio frequency signals that has an input and an output, comprising,

• (a) a passive variable relatively wider band pass filter, tunable to said frequency F having an input and an output,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) phase reversing means for receiving said passive filter output producing phase reversed signals,
• (d) means for combining said phase reversed signals with said electrical path output, producing a combined signal output,
• (e) said electrical path input, said means for sampling, said passive filter and said phase reversing means being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said electrical path being coupled electrically in parallel with the output of each coupled to said means for combining and
• (g) means for varying said passive filter whereby a narrow band notch at the frequency F is in the frequency spectrum of radio frequency signals from said combining means.

In a radio receiver for receiving desired signals in a predetermined frequency band and having means for eliminating a particular narrow frequency band of received signals among the desired signals in an electrical path in the receiver that has an input and an output, the improvement comprising,

• (a) a passive variable narrow band pass filter, tunable to the frequency of said undesired narrow band having an input and an output,
• (b) means for sampling signals in said electrical path at said input thereof and feeding said sample to said passive filter input,
• (c) means for subtracting the signals of said sample that reach the output of said passive filter from said electrical path output, producing a net signal output and
• (e) said radio receiver electrical path input, said means for sampling and said passive filter being coupled together in electrical series, in that order, herein called the series filter circuit,
• (f) said series filter circuit and said radio receiver electrical path being coupled electrically in parallel with the output of each coupled to said means for subtracting signals and
• (g) means for varying said passive filter to insure that said undesired signals are substantially eliminated from said received signals in said net signal output.