Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1979-12-11
1982-04-06
Olms, Douglas W.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
455114, 332 21, 329167, H04H 500
Patent
active
043237312
ABSTRACT:
A compatible AM stereo system employing a modified quadrature modulation scheme where the gain in the quadrature-phased channel, and thus the phase angle between the L and R modulated phase components of the composite modulated signal, is dynamically varied in accordance with changing modulation conditions. The average phase angle between the L and R modulated phase components is much greater than was previously possible in fixed gain systems, thus signal-to-noise ratio (SNR) in stereophonic receivers is improved. In the transmitter (FIGS. 3, 7A and 7B), a matrix circuit (40, 188) adds and subtracts L and R audio signals to produce sum (L+R) and difference (L-R) signals. An analog divider (54; 194, 200) adjusts the gain of the (L-R) signal in accordance with a gain control signal A.sub.Q. The (L+R) and gain adjusted (L-R) signals are transmitted on two quadrature-phased carriers by a quadrature AM (QAM) transmitter (50, 160). A distortion estimator (56, 190, FIGS. 5A and 5B) calculates the amount of distortion which the envelope of the composite modulated signal will produce in a conventional monophonic receiver and dynamically adjusts the gain control signal A.sub.Q to maximize gain without exceeding predetermined distortion constraints. A circuit (60, 210, FIGS. 9 and 10) generates a pilot signal and modulates it with the dynamically varying gain control. This pilot signal is added to, and thus transmitted with, the gain adjusted (L-R) signal. In one transmitter embodiment (FIGS. 7A and 7B), a circuit (156, FIG. 8) is provided for compressing low amplitude audio signals so as to further improve SNR. A signal indicative of the amounts of compression is also modulated onto the pilot signal, and thus transmitted to the receiver. A filter network (154) provides a gap in the low frequency portion of the (L-R) signal into which the pilot signal may be inserted, and processes the (L+R) and (L-R) signals so that no loss in bass occurs as a result of this filtering. Stereophonic receivers (FIGS. 11-13) are disclosed which demodulate the pilot signal and control the gain of the recovered (L+R) and (L-R) signals in accordance therewith so as to track the varying phase angle and signal compression of the composite modulated signal, and thus optimally recover the L and R audio signals in their original form. The system may easily be converted into an improved independent sideband (ISB) system by the insertion of appropriate phase delays in the (L+R) and (L-R) signal paths.
REFERENCES:
patent: 3067293 (1962-12-01), Moore
patent: 3295072 (1966-12-01), Van Kessel
patent: 3378772 (1968-04-01), Van Kessel et al.
patent: 3449715 (1969-06-01), Van Kessel
patent: 4194154 (1980-03-01), Kahn
patent: 4225751 (1980-09-01), Hershberger
Harris Corporation
Olms Douglas W.
LandOfFree
Variable-angle, multiple channel amplitude modulation system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Variable-angle, multiple channel amplitude modulation system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable-angle, multiple channel amplitude modulation system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-593851