| 摘要 |
radio engineering; panoramic receivers and spectrum analyzers. SUBSTANCE: frequency changer has two mixers, two intermediate-frequency amplifiers, two adders, four switches, heterodyne, two +90 deg. phase shifters, -90 deg. phase shifter, two multipliers, four narrow-band filters, and four amplitude detectors. EFFECT: provision for extending signal frequency search band without extending heterodyne frequency re-tuning range. 2 dwg
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