Method and apparatus for testing microwave repeaters for IM distortion
AssigneeBell Telephone Laboratories, Incorporated
InventorHotze Miedema
Life of this patent
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Abstract
Microwave repeaters and the like are tested for third-order IM distortion by applying two, swept-frequency test-tones to the repeater. The test-tones are offset by a fixed frequency difference .delta.. A detector circuit, connected to the output of the repeater, measures the amplitude of any signal component of frequency 2.delta. which is a direct measure of the repeater's non-linearity. Because a signal component of frequency 2.delta. can be generated by second-order distortion within the detector itself, the detector includes special circuitry to cancel out any such unwanted term.
Claims14
Apparatus for measuring the non-linearity of a device subject to distortion, which comprises:
- means for generating a first signal of frequency f.sub.o ;
- means for generating a second signal of frequency (f.sub.o +.delta.), where .delta. is an offset frequency which is small compared to the bandwidth of the device under test;
- means for generating a third signal of swept frequency f;
- means for combining said first, second and third signals thereby to generate first and second test signals of frequency (f.sub.o +f) and (f.sub.o +.delta.+f) respectively, the frequencies f.sub.o, f and .delta. being selected such that the test signals scan the band of interest, said test signals being applied to the input of the device under test;
- and
- detector means, connected to the output of the device under test, for measuring the amplitude of any component in the output signal for the device under test of frequency (f.sub.o -.delta.+f) or (f.sub.o +2.delta.+f), said measuring means including means for cancelling any component of frequency 2.delta. caused by distortion within the detector means itself.
Apparatus for measuring the non-linearity of a device subject to distortion, which comprises:
- means for generating a first signal of frequency f.sub.o ;
- means for generating a second signal of frequency (f.sub.o +.delta.), where .delta. is an offset frequency which is small compared to the bandwidth of the device under test;
- means for generating a third signal of swept frequency f;
- means for combining said first, second, and third signals thereby to generate first and second test signals of frequency (f.sub.o +f) and (f.sub.o +.delta.+f), respectively, the frequency f.sub.o, f and .delta. being selected such that the test signals scan the band of interest, said test signals being applied to the input of the device under test;
- means for generating a fourth signal of swept frequency (f+.alpha.), where .alpha. is an offset frequency which is small compared to the bandwidth of the device under test;
- and
- detector means, connected to the output of the device under test and to the output of said fourth signal generating means, for measuring the amplitude of a selected intermodulation product, the amplitude of said selected intermodulation product being directly proportional to the non-linearity of the device under test, said detector means further including means for cancelling any signal component of the same frequency as the intermodulation product of fixed frequency generated by fourth-order non-linearity in the output from said fourth signal generating means.
Dependencies are inferred from the claim text.