Phase lock loop multitone interference canceling system

• US 4,027,264 A
• Filed: 02/24/1976
• Issued: 05/31/1977
• Est. Priority Date: 02/24/1976
• Status: Expired due to Term

• Current Assignee: The United States Of America As Represented By The Secretary Of The Army
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Gutleber, Frank S.
• Primary Examiner(s): Heyman, John S.
• Application Number:
  US05/660,965
• Time in Patent Office: 462 Days
• Field of Search: 325/474, 325/475, 325/476, 325/477, 328/165, 328/167, 329/122, 329/123, 329/124, 329/130, 329/133, 329/168, 329/170, 179/1 P
• US Class Current: 455/306
• CPC Class Codes: H03D 3/248 with means for eliminating interfering signals, e.g. by multiple phase locked loops multiple loops in general H03L7/07, H03L7/22
• CPC Class Codes: H03L 7/07 using several loops, e.g. for redundant clock signal generation
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system

Abstract

An interference canceling system in which a phase lock loop is utilized as narrow band tracking filter to adaptively lock to interference tones to be canceled by a process of signal subtraction.

Claims

1. In a communication system for removing at least one undesired interfering continuous wave frequency from incoming wave energy including a wideband intelligence-bearing signal, an interference cancellation network for each said interfering frequency comprising:

an ultra-narrow bandwidth phase lock loop continuously receptive of said input wave energy and capable of continuously tracking only said interfering continuous wave frequency,

said phase lock loop including a voltage controlled oscillator which can be swept in frequency over the spectral range of the intelligence-bearing signal until the interfering frequency is encountered,

said phase lock loop further including a phase detector coupled to said oscillator and to said incoming wave energy and a narrow band low pass filter.

the output of said oscillator being a replica of said interfering continuous wave frequency, and

circuit means responding to the output of said oscillator and to said incoming wave energy for canceling from said incoming wave energy said interfering continuous wave frequency only while said oscillator is frequency locked to the interfering frequency.

2. A system as recited in claim 1 wherein said incoming wave energy includes a plurality of interfering frequencies and comprising a like plurality of cascaded interference cancellation networks, each phase lock loop being set to lock on a different one of said interfering frequencies.

3. A system as set forth in claim 1 further including

means for indicating that said phase lock loop has locked to said interfering frequency;

and wherein

said circuit means includes a 90 degree phase shifter and a variable amplifier responding to said 90 degree phase-shifted oscillator output,

a subtractor coupled to said incoming wave energy, and

means for coupling the output of said variable amplifier to said subtractor only while the lock condition is indicated.

4. A system as recited in claim 3 wherein said means for indicating includes phase detection means responsive to the 90 degree phase-shifted output of said oscillator and to said incoming wave energy and an integrator, said means for indicating providing a direct current voltages indicative of a lock to said interfering continuous wave frequency.

5. The system as recited in claim 4 including means for adjusting the gain of said amplifier to provide complete subtraction of said interfering continuous wave frequency from said incoming wave energy while said phase lock condition is indicated.

6. A system as recited in claim 5 wherein said means for adjusting includes a null detector connected in the output of said subtractor and coupled to said amplifier.

7. The system as recited in claim 4 wherein the output of said means for indicating is representative of the level of said interfering frequency, and including means for adjusting the gain of said amplifier in accordance with the output of said means for indicating to provide complete cancellation of said continuous wave frequency from said incoming wave energy while said phase lock condition is indicated.