Simulcast transmission system having phase-locked remote transmitters
First Claim
1. In a simulcast transmission system having a central station for controlling via communication paths the operation of transmitters at a plurality of remote stations, said simulcast transmission system including improvement for automatically phase locking the frequency of the transmitter signals of the remote stations, comprising:
- (a) said central station including;
(1) an oscillator for providing a reference signal of a predetermined first frequency; and
(2) a transmitter for transmitting via the communication paths the reference signal; and
(b) each of said remote stations including;
(1) a receiver for receiving via the communication path the transmitted reference signal;
(2) a signal conditioner for providing a conditioned reference signal from the received reference signal, said signal conditioner including;
(i) a first phase-locked loop including a forward path having a phase comparator, an analog switch, a loop filter, sample and hold circuitry and a voltage-controlled crystal oscillator (VCXO) coupled in series, and a feedback path having a first divider coupled to the VCXO for providing a feedback signal to the phase comparator;
(ii) a second divider coupled to the VCXO for providing the conditioned reference signal of a predetermined second frequency;
(iii) a detector for detecting the presence of the received reference signal and providing an activity indication signal when the received reference signal is present; and
(iv) control means for opening the analog switch, enabling the sample and hold circuitry to maintain the frequency of the VCXO and providing a reset signal to reset the first divider to a predetermined state in the absence of the activity indication signal, the control means closing the analog switch, enabling the sample and hold circuitry to sample the output of the loop filter for controlling the frequency of the VCXO, and removing the reset signal from the first divider in response to the presence of the activity indication signal;
(3) a second phase-locked loop responsive to the conditioned reference signal for providing an intermediate signal of a predetermined third frequency; and
(4) a multiplier for multiplying the intermediate signal to provide a transmitter signal of a predetermined fourth frequency.
0 Assignments
0 Petitions
Accused Products
Abstract
A simulcast transmission system is provided where a reference signal transmitted from a central station is utilized to phase-lock transmitters located at remote stations. The remote stations include a receiver for receiving the transmitted reference signal and a signal conditioner for conditioning the received reference signal for application to the transmitters. The transmitters include a phase-locked loop which may be followed by a multiplier for providing transmitter signals of predetermined frequencies. All the transmitters at the remote stations are phase locked to the reference signal transmitted from the central station. In the event that the reference signal transmitted by the central station is interrupted, the signal conditioner of the remote stations will operate in an open-loop fashion to provide the conditioned reference signal during the interruption. After the interruption has cleared, the signal conditioner is automatically phase synchronized to the reference signal and closed-loop operation is resumed.
49 Citations
15 Claims
-
1. In a simulcast transmission system having a central station for controlling via communication paths the operation of transmitters at a plurality of remote stations, said simulcast transmission system including improvement for automatically phase locking the frequency of the transmitter signals of the remote stations, comprising:
-
(a) said central station including; (1) an oscillator for providing a reference signal of a predetermined first frequency; and (2) a transmitter for transmitting via the communication paths the reference signal; and (b) each of said remote stations including; (1) a receiver for receiving via the communication path the transmitted reference signal; (2) a signal conditioner for providing a conditioned reference signal from the received reference signal, said signal conditioner including; (i) a first phase-locked loop including a forward path having a phase comparator, an analog switch, a loop filter, sample and hold circuitry and a voltage-controlled crystal oscillator (VCXO) coupled in series, and a feedback path having a first divider coupled to the VCXO for providing a feedback signal to the phase comparator; (ii) a second divider coupled to the VCXO for providing the conditioned reference signal of a predetermined second frequency; (iii) a detector for detecting the presence of the received reference signal and providing an activity indication signal when the received reference signal is present; and (iv) control means for opening the analog switch, enabling the sample and hold circuitry to maintain the frequency of the VCXO and providing a reset signal to reset the first divider to a predetermined state in the absence of the activity indication signal, the control means closing the analog switch, enabling the sample and hold circuitry to sample the output of the loop filter for controlling the frequency of the VCXO, and removing the reset signal from the first divider in response to the presence of the activity indication signal; (3) a second phase-locked loop responsive to the conditioned reference signal for providing an intermediate signal of a predetermined third frequency; and (4) a multiplier for multiplying the intermediate signal to provide a transmitter signal of a predetermined fourth frequency. - View Dependent Claims (2, 3, 4, 5, 6)
-
-
7. In a simulcast transmission system having a central station for controlling via microwave communication paths the operation of transmitters of a plurality of remote stations, said simulcast transmission system including improvement for automatically phase locking the frequency of the transmitter signals of the remote stations, comprising:
-
(a) said central station including; (1) an oscillator for providing a reference signal of a predetermined first frequency; and (2) a transmitter for transmitting via the microwave communication paths the reference signal; and (b) each of said remote stations including; (1) a receiver for receiving via the microwave communication path the transmitted reference signal; (2) a signal conditioner including; (i) a first phase-locked loop including a forward path having a phase comparator, loop filter, an analog switch, sample and hold circuitry and a voltage-controlled crystal oscillator (VCXO) and a feedback path having a first divider coupled to the VCXO for providing a feedback signal to the phase comparator, (ii) a second divider coupled to the VCXO for providing a first conditioned reference signal of a predetermined second frequency; (iii) a first monostable device for detecting the received reference signal to provide an activity indication signal; (iv) a flip-flop responsive to the activity indication signal and the received reference signal for providing a reset signal for resetting the first divider to phase synchronize the output signal of the first divider to the received reference signal; and
the analog switch closing the forward path to the VCXO and the sample and hold circuitry being enabled to sample in response to the activity indication signal;(c) a second phase-locked loop responsive to the first conditioned reference signal for providing a first intermediate signal of a predetermined third frequency; and (d) a first multiplier for multiplying the first intermediate signal to provide a transmitter signal of a predetermined fourth frequency. - View Dependent Claims (8, 9)
-
-
10. In a transmission system for distributing a reference signal from a central station to a plurality of remote stations via communication paths therebetween, each remote station including a signal conditioner for providing a conditioned reference signal from the reference signal received thereat, said signal conditioner comprising:
-
(a) phase-locked loop means coupled to the received reference signal, said phase-locked loop means including a forward path having phase comparator means, analog switch means, loop filter means, sample and hold means and voltage-controlled crystal oscillator (VCXO) means coupled in series, and a feedback path having a first dividing means coupled to the VCXO means for providing a feedback signal to the phase comparator means; (b) second dividing means coupled to the VCXO means for providing the conditioned reference signal; (c) means coupled to the received reference signal for detecting the presence of the received reference signal and providing an activity indication signal when the received reference signal is present; and (d) control means for opening the analog switch means, enabling the sample and hold means to maintain the frequency of the VCXO means and providing a reset signal to reset the first dividing means to a predetermined state in the absence of the activity indication signal, the control means thereafter closing the analog switch means, enabling the sample and hold means to sample the output of the loop filter means for controlling the frequency of the VCXO means, and removing the reset signal from the first dividing means in response to the presence of the activity indication signal. - View Dependent Claims (11, 12)
-
-
13. In a simulcast transmission system having a central station for controlling via communication paths the operation of transmitters at a plurality of remote stations, said simulcast transmission system including improvement for automatically phase locking the frequency of the transmitter signals of the remote stations, comprising:
-
(a) said central station including; (1) an oscillator for providing a reference signal of a predetermined frequency; and (2) a transmitter for transmitting via the communication paths the reference signal; and (b) each of said remote stations including; (1) a receiver for receiving via the communication path the transmitted reference signal; (2) a signal conditioner for providing a conditioned reference signal from the received reference signal, said signal conditioner including; (i) a first phase-locked loop including a forward path having a phase comparator, an analog switch, a loop filter, sample and hold circuitry and a voltage-controlled crystal oscillator (VCXO) coupled in series, and a feedback path having a first divider coupled to the VCXO for providing a feedback signal to the phase comparator; (ii) a second divider coupled to the VCXO for providing the conditioned reference signal of a predetermined frequency; (iii) a detector for detecting the presence of the received reference signal and providing an activity indication signal when the received reference signal is present; and (iv) control means for opening the analog switch, enabling the sample and hold circuitry to maintain the frequency of the VCXO and providing a reset signal to reset the first divider to a predetermined state in the absence of the activity indication signal, the control means closing the analog switch, enabling the sample and hold circuitry to sample the output of the loop filter for controlling the frequency of the VCXO, and removing the reset signal from the first divider in response to the presence of the activity indication signal; and (3) a second phase-locked loop responsive to the conditioned reference signal for providing an output signal of a predetermined frequency to the transmitter. - View Dependent Claims (14, 15)
-
Specification