System and method for improved detection of AM signals

Details System and method for improved detection of AM signals System and method for improved detection of AM signals

2005-01-06

2009-12-29

Mei, Xu (Department: 2614)

Electrical audio signal processing systems and devices

Binaural and stereophonic

Broadcast or multiplex stereo

C329S327000, C329S358000, C329S359000, C455S150100, C455S196100, C455S255000

Reexamination Certificate

active

07639821

ABSTRACT:
A software defined radio detects an amplitude modulated (AM) signal contained within a received signal. This detection involves first receiving a radio frequency (RF) signal that contains the AM signal modulated about a carrier frequency (fc). The RF signal is downconverted using a first local oscillator having a frequency flo. An in-phase (I) channel signal and a quadrature (Q) channel signal are produced. From the I-channel signal, a relationship between the carrier frequency and the frequency of the local oscillator is determined with a frequency detector. The downconverted carrier signal of the I-channel signal is used to create a second set of signals with proper phases and frequencies that can be used to rotate the I-channel and Q-channel signals to account for differences between the downconverted fcand DC. From the I-channel and Q-channel signals, a phase difference between the I-channel and Q-channel signals is determined so that the processed I-channel and Q-channel signals can be properly combined. Properly combining the processed (rotated) I-channel and Q-channel signals results in a demodulated AM signal.

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patent: 5222144 (1993-06-01), Whikehart
patent: 5561716 (1996-10-01), Kasser et al.

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