Multichannel FM subcarrier broadcast system

• US 4,782,531 A
• Filed: 06/23/1987
• Issued: 11/01/1988
• Est. Priority Date: 06/23/1987
• Status: Expired due to Fees

• Current Assignee: Andrew Barber, Davis, Steven J., Lawrence J. Karr
• Original Assignee: Andrew Barber, Davis, Steven J., Lawrence J. Karr
• Inventors: Davis, Steven J., Barber, Andrew, Karr, Lawrence J.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US07/065,911
• Time in Patent Office: 497 Days
• Field of Search: 332/23 A, 455/45, 381/2, 381/3, 381/4, 381/14, 381/15, 381/16, 375/39
• US Class Current: 381/14
• CPC Class Codes: H04H 20/34 using an out-of-band subcarrier signal

Abstract

A multichannel FM subcarrier broadcast system is disclosed which enables the transmission of multiple independent signals by generating independent sidebands of suppressed carriers in the subcarrier band of an FM transmitting station. Transmitting and receiving apparatus is disclosed which employs phase shift networks to minimize interchannel distortion, thus allowing close spacing of adjacent sidebands.

Claims

1. A multichannel FM subcarrier transmission system for providing a transmitter modulation signal for broadcasting first and second information signals as independent sidebands of a suppressed carrier in the subcarrier band of an FM transmitting station, comprising:

filter means for limiting the bandwidth of the first and second information signals to predetermined values to provide first and second filtered signals;

summing means for providing a sum signal which is the sum of the first and second filtered signals;

difference means for providing a difference signal which is the difference between the first and second filtered signals;

phase shift means for shifting the phase of the sum signal by a first amount to provide a first phased signal, and for shifting the phase of the difference signal by a second amount to provide a second phased signal, where the first and second amounts are chosen to provide a 90°

phase difference between the sum and difference signals;

first mixing means for mixing the first phased signal with the sine of the suppressed carrier to provide a first mixed signal;

second mixing means for mixing the second phased signal with the cosine of the supressed carrier to provide a second mixed signal;

second summing means for summing the first and second mixed signals to provide the transmitter modulation signal;

and means for applying the transmitter modulation signal to frequency modulate a carrier wave.

2. A multichannel FM subcarrier receiver system for recovering from the FM demodulated signal of an FM tuner first and second information signals broadcast as independent sidebands of a suppressed carrier in the subcarrier band of an FM transmitting station, comprising:

filter means for limiting the bandwidth of the FM demodulated signal to the subcarrier band of the FM transmitting station, providing a filtered signal;

first and second mixing means for mixing the filered signal with respectively, the sine and cosine of the suppresssed carrier to thus provide first and second mixed signals;

phase shifting means for shifting the phase of the first mixed signal by a first amount to provide a first phased signal, and, for shifting the phase of the second mixed signal by a second amount to provide a second phased signal, where the first and second amounts are chosen to provide a 90°

phase difference between the first and second phased signals;

summing means for providing, respectively, the sum of and the difference between the first phased and the second phased signals to provide, respectively, sum and difference signals;

second filter means for removing the suppressed carrier from the sum and difference signals to provide respectively, the first and second information signals.