| 摘要 |
A modulated signal comprising a modulation signal impressed upon a carrier signal is heterodyne converted downward to shift the frequency spectrum of the modulated signal into an intermediate frequency band located between a carrier frequency band containing the carrier frequency of the carrier signal and a modulation frequency band containing the modulation frequencies of the modulation signal. In the intermediate frequency band, the modulated signal is fed through a tuned bridge-T filter circuit having a generally V-shaped amplitude versus frequency response curve exhibiting a center frequency lying within the frequency spectrum of the modulated signal to amplitude and phase distort the modulated signal to simulate multipath reception. Preferably, the filter network is tuned by a voltage variable capacitor which responds to a unidirectionally varying control voltage to effectively sweep the V-shaped filter response curve through the frequency spectrum of the modulated signal to simulate movement of a receiving antenna through a multipath reception area. After introduction of the desired amplitude and phase distortion, the modulated signal is heterodyne converted upward to shift the frequency spectrum of the modulated signal back to the carrier frequency band.
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