Simulcast transmission system

• US 4,608,699 A
• Filed: 12/27/1982
• Issued: 08/26/1986
• Est. Priority Date: 12/27/1982
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Kurby, Christopher N., Batlivala, Percy P.
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US06/453,846
• Time in Patent Office: 1,338 Days
• Field of Search: 375/3, 375/5, 375/7, 375/8, 375/81, 375/45, 455/7, 455/31, 455/73, 455/78, 455/51, 455/52, 455/53, 455/56, 331/23
• US Class Current: 375/216
• CPC Class Codes: H04H 20/67 Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency
• CPC Class Codes: H04L 27/10 Frequency-modulated carrier systems, i.e. using frequency-shift keying H04L27/32 takes precedence

Abstract

An improved simulcast transmission in which a signal transmitted by a master station provides a reference frequency signal, as well as a voice and data path, is described. The system can be configured such that a master station can transmit AFSK data and voice or FSK data and voice. In either case, the remote transmitter will retransmit FSK and voice.

Claims

1. An improved simulcast transmission system having a master transmitter and a plurality of phase-locked remote receiver and simulcast transmitter units wherein a transmitted carrier signal provides a reference signal for the simulcast transmitters used at the remote transmitter sites to distribute a simulcast signal, comprising:

means for receiving a carrier signal;

phase-locked loop means including a first electronic switch means for phase locking to the received carrier signal and providing a phase-locked reference signal to said remote simulcast transmitters, wherein said first electronic switch means opens the phase-locked loop in response to a signal;

discriminator means coupled to said receiving means for recovering a base-band signal of audio and encoded data;

modem means coupled to said discriminator means to recover the data signal from said modem means comprising the base-band signal;

data detector means coupled to said modem means and said first electronic switch means, to sense the presence of data, and activate or deactivate said first electronic switch;

a second electronic switch means coupled to said discriminator means and responsive to said data detector means to block the audio signal in the presence of data; and

summing network means coupled to said modem means and to said second electronic switch means for providing a modulation signal to the remote transmitters comprising the combined audio and data signals.

3. The apparatus of claim 1 wherein the receiving means includes a bandpass filter and a frequency divider.

4. The apparatus of claim 1 wherein the modem is configured to decode audio frequency-shifted keying (AFSK) data.

5. The apparatus of claim 1 wherein said phase locked loop includes a phase detector, a low pass filter, a voltage controlled crystal oscillator and an electronic switch.

2. An improved simulcast transmission system having a master transmitter, which transmits modulated audio and frequency-shifted keying (FSK) data at reduced deviation and a plurality of phase-locked remote receiver and simulcast transmitter units utilizing a transmitted carrier signal for providing a reference signal for the phase-locked loop receivers and simulcast transmitters used at the remote sites comprising;

means for receiving a carrier signal;

phase-locked means for phase locking to the received carrier signal for providing a radio frequency (RF) reference signal to said simulcast remote transmitters;

discriminator means coupled to said receiving means for recovering the audio or modulated data signal;

data detector means coupled to said discriminator means for sensing the presence of FSK data;

first electronic switch means coupled to said discriminator means responsive to said for controlling the audio signal;

second electronic switch means coupled to said discriminator means and responsive to said data detector means for controlling the data signal;

a first amplifier means coupled to said first electronic switch means for compensating the FSK signal level;

a second amplifier means coupled to said second electronic switch means for compensating the FSK signal level; and

the output of first amplifier means coupled to the output of said second amplifier means providing a modulation signal to the volatage controlled oscillator of said phase-locked loop means.

6. The apparatus of claim 2 wherein the receiving means includes a bandpass filter and a frequency divider.

7. The apparatus of claim 2 wherein the amplifier in the audio path is configured to compensate the audio signal for unity gain through the receiver circuitry.

8. The apparatus of claim 2 wherein the amplifier in the data path is configured to provide a gain which is the inverse of the phase locked loop multiplication factor.

9. The apparatus of claim 2 wherein said phase locked loop includes a phase detector, a low pass filter, and a voltage controlled oscillator.

10. An improved method for simulcast transmission including the steps of:

receiving a transmitted carrier signal;

phase locking to the received carrier signal and providing a phase locked radio frequency (RF) reference signal to the remote transmitters by a phase locked loop including a voltage controlled oscillator;

recovering a base-band signal of audio and encoded data from a carrier signal;

recovering the data signal from the base-band signal;

detecting the presence of data;

opening the phase locked loop in the presence of data;

blocking the audio signal in the presence of data;

summing the audio and the recovered data signal; and

directly modulating the voltage controlled oscillator with the combined audio and data signal.

11. An improved method for simulcast transmission in a system having a master transmitter, a plurality of receivers and a plurality of remote simulcast transmitters coupled to said receivers including the steps of:

receiving, with a receiver, a transmitted carrier signal transmitted from said master transmitter, said transmitted carrier signal being modulated with an audio or data signal;

phase locking to the received carrier signal and providing a phase locked radio frequency (RF) reference signal to the remote simulcast transmitters;

recovering the audio or modulated data signal with a first phase locked loop;

sensing the presence of frequency-shifted keying (FSK) data or audio;

blocking the audio signal in the presence of data;

blocking the data signal in the presence of audio;

compensating the audio signal level for unity gain through the receiver circuitry;

compensating the data signal modulation level to a level equal to the inverse of the multiplication ratio of the phase locked loop;

combining the compensated audio and compensated data signals; and

directly modulating a second voltage controlled crystal oscillator of the second phase locked loop with combined audio and data signal wherein the output of said second phase locked loop is directly multiplied and amplified to provide said simulcast transmission signal.