United States Patent [191
`Cannalte et al.
`-
`
`[54] SIMULCAST TRANSMISSION SYSTEM
`HAVING PHASE-LOCKED REMOTE
`TRANSMI'ITERS
`[75] Inventors: Gary A‘ Cammlte’ Hoffman Estates;
`.
`Ronald H. Chapman, Wheaten;
`Walter J. Rozanslu, Jr.,
`Schaumburg, all of I11.
`_
`[73] Asslgneei Motorola, 1110-, schaumbul'g, 111-
`[21] APPL N05 894,671
`_
`AP!" 10’ 1978
`[22] F?ed‘
`[51] Int. Cl.2 ............................................. .. H04B 7/00
`[52] US. Cl. .................................... .. 325/58; 325/17;
`325/63; 343/179
`3275/58, 63! 53, 54,
`325/17; 343/179
`
`[58] Field of Search... ..............
`
`[56]
`
`References Cited
`
`2,067,353
`
`Us‘ PATENT DOCUMENTS
`1/1937 Snow ................................... .. 325/63
`llflobqy?shi at al
`4,119,912 10/1978 Nagy et al. ......................
`
`,
`
`,
`
`artmez .......... ..
`
`325/58
`
`[11]
`[45]
`
`4,188,582
`Feb. 12, 1980
`
`Attorney, Agent, or Firm—Rolland R. Hackbart; James
`W. Gillman
`{ABSTRACT
`[57]
`A simulcast transmission system is provided where a
`reference signal transmitted from a central station is
`.
`.
`.
`.
`utilized to phase-lock transmltters located at remote
`.
`.
`.
`.
`.
`.
`.
`stations. The remote stations Include a receiver for re
`ceiving the transmitted reference signal and a signal
`conditioner for conditioning the received reference
`signal for application to the transmitters. The transmit
`ters include a phase-locked loop which may be followed
`by a multiplier for providing transmitter signals of pre
`determined frequencies. All the transmitters at the re
`mote 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 sta
`tions will operate in an open-loop fashion to provide the
`conditioned reference signal during the interruption.
`After the interruption has cleared, the signal condi
`tioner is automatically phase synchronized to the refer
`
`“we sxgnal and "1
`
`-
`
`osed_
`
`1°°p operauon ‘8 resumed‘
`
`-
`
`-
`
`Primary Examiner-Marc E. Bookbinder
`
`15 Claims‘ , 7 Drawing Figures
`
`I
`
`1 O 2
`‘ f
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`
`PLL
`
`TRANS" l TTER
`(F1 1
`
`‘
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`1 O 6
`
`REMOTE STATION
`
`'
`
`SIGNAL
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`CONDITIONER
`RECEIVER
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`CENTRAL STATION
`1 0 0
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`\
`\
`11 I CRDNAVE
`REFERENCE
`TRANSMITTER
`OSCILLATOR
`o 3
`1 0 5
`(
`SIGNAL
`CONDITIONER
`
`%
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`RECEIVER
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`‘
`
`1° 7
`PLI-
`
`1 1 1 if
`RANSMHTER
`( F2 1
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`TRANSMITTER
`(H )
`
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`1 1 2)
`
`1 0 9‘
`'
`
`1 1 3
`TRANSN I TTER
`(F21
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`i
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`l
`
`Juniper Ex 1015-p. 1
`Juniper v MTel403
`
`

`
`US. Patent Feb. 12, 1980
`
`Sheet 1 of2
`
`4,188,582
`
`102
`(
`MICROWAVE
`. RECEIVER
`
`6E<
`
`REMOTE STATION
`
`104
`
`"
`
`TRANSMITTER
`(F1 I
`
`"
`
`SIGNAL
`CONDITIONER
`
`IOI
`
`\
`
`CENTRAL STATION (1 00
`
`‘I N _
`
`_
`
`TRANSMITTER
`(F2)
`
`_
`
`
`
`MIcRONAvE TRANSMITTER
`
`
`
`REFERENCE OSCILLATOR
`
`% I103
`MICROWAVE _.|
`
`RECEIVER
`
`{105
`SIGNAL
`
`CONDITIONER ‘
`
`'
`
`
`
`' 108 w E -
`
`
`
`TRANSMITTER
`
`v TRANSMITTER
`(F21
`
`(200
`
`ATOMII:
`CLOCK
`
`REMOTE STATION
`
`201
`
`(202
`
`4
`
`PL"
`
`V 20 4
`
`, TRANSMITTER _
`(F1 I
`
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`
`SIGNAL .
`CONDITIONER
`
`I
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`203
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`Pu‘
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`A
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`(F2)
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`1-15-52
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`\205
`
`CONDITIONED
`REF- SIGNAL
`
`T
`
`300
`
`MODULATION
`
`TRANSMITTER -
`SIGNAL
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`I
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`[303
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`r302
`V-C IXIOI
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`
`DIVIDER
`
`Juniper Ex 1015-p. 2
`Juniper v MTel403
`
`

`
`US. Patent Feb. 12, 1980
`
`Sheet 2 of 2
`
`4,188,582
`
`REFERENCE
`SIGNAL
`
`4;] 1
`
`4'02
`
`CONDITIONED
`9-...- D I v I DER
`REF. SIGNAL A 408% H
`V
`
`F “ER
`4 0 0
`
`LIMITER
`#1
`
`PHASE
`“l COMPARATOR
`
`SAMPLE &
`HOLD
`
`~ VCXD _'
`4 0 7
`
`L 1 M ITER ‘
`#2
`
`Low
`FILTER
`
`SWITCH
`
`[- DIVIDER
`
`'
`
`CONDITIONED
`REF. SIGNAL B
`
`404 f T DIVIDER:k—— 9
`F 40
`ACTIVITY DETECTOR
`AND RESET
`SYNCHRONIZER
`
`410
`
`LmlTER '
`
`3.1-5.5
`#2
`f‘
`T
`RESETTABLE
`MONOSTABLE
`#1
`
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`#2
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`DIVIDER
`RESET
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`610
`Mom. #1
`MOND- #2
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`LIHITER #2 6123 I
`
`DIVIDER RESET______|-6—13—;|_ CONTROL SIGNAL F 5 1 4
`
`
`(700
`\
`ATOMIC
`CLOCK
`
`70 1
`(
`Home
`CLOCK
`
`702
`
`DIVIDER
`
`DIVIDER —
`‘L
`703
`7° 43
`mvwER
`
`DIVIDER
`
`CONDITIONED
`REFERENCE
`7 Us
`SIGNAL A
`»
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`ACTIVITY
`DETECTOR
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`
`Juniper Ex 1015-p. 3
`Juniper v MTel403
`
`

`
`1
`
`SIMULCAST TRANSMISSION SYSTEM HAVING
`PHASE-LOCKED REMOTE TRANSMITI'ERS
`
`10
`
`4,188,582
`2
`reference signal but also maintained during brief inter
`ruptions of the reference signal.
`It is yet a further object of the present invention to
`provide an improved simulcast transmission system
`having phase-locked remote transmitters whose fre
`quencies are accurately and reliably maintained, im
`mune to aging and relatively immune to environmental
`variations.
`.
`Briefly described, the invention is a simulcast trans
`mission system having a central station for controlling
`via a communication path the operation of transmitters
`at a plurality of remote stations. The simulcast transmis
`sion system further includes improvement for automati
`cally phase locking the frequencies of the remote trans
`mitter signals. At the central station, a reference oscilla
`tor provides a reference signal of a predetermined ?rst
`frequency that is transmitted via the communication
`path to the remote stations. Each remote station in
`cludes a receiver for receiving via the communication
`path the transmitted reference signal, a signal condi
`tioner for conditioning the received reference signal
`and, for each transmitter, a phase-locked loop respon
`sive to the conditioned reference signal for providing an
`intermediate signal of a predetermined second fre
`quency and a multiplier for multiplying the intermediate
`signal to provide the transmitter signal of a predeter
`mined third frequency.
`Additional features, objects and advantages of the
`simulcast transmission system in accordance with the
`present invention will be more clearly apprehended
`from the following detailed description together with
`the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a functional block diagram of a simulcast
`transmission system embodying the present invention.
`FIG. 2 is a functional block diagram of a remote
`station of a simulcast transmission system in accordance
`with the present invention.
`FIG. 3 is a block diagram of the phase-locked loop
`and transmitter shown in FIG. 1.
`FIG. 4 is a block diagram of the signal conditioner
`shown in FIG. 1.
`FIG. 5 is a block diagram of the activity detector and
`reset synchronizer of FIG. 4.
`FIG. 6 is a timing diagram for the activity detector
`and reset synchronizer of FIG. 5.
`FIG. 7 is a block diagram of the signal conditioner of
`FIG. 2.
`
`45
`
`RELATED APPLICATIONS
`This application is related to the instant assignees
`copending patent application Ser. No. 815,885 entitled
`"Simulcast TransmissionSystem” by James L. Osborn
`and filed on July 15, 1977.
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to a phase-locked transmission
`system and, more particularly, to a simulcast transmis
`sion system having a plurality of phase-locked remote
`transmitters.
`2. Description of the Prior Art
`Simultaneous broadcast, or simulcast transmission
`systems, typically have a plurality of remote transmit
`ters that simultaneously broadcast identical audio or
`information signals at substantially the same carrier
`frequency. By using a number of geographically diverse
`transmitters, a simulcast system provides maximum
`signal coverage to topographically irregular geographi
`25
`cal areas, such as mountainous regions, where unob
`structed radio coverage is not possible.
`The performance of simulcast transmission systems is
`greatly degraded if the transmitters assignedthe same
`frequency are not operating on substantially the exact
`same frequency. Frequency offset between transmitters
`causes audible interference in the form of beat noise.
`This problem has been typically solved by utilizing very
`high stability oscillators in each of the transmitters.
`However, such an approach is expensive and has a
`number of problems including temperature susceptibil
`ity and frequency drift caused by aging of the high
`stability oscillator necessitating costly ‘periodic mainte
`nance.
`The problem of frequency drift is more critical for
`transmission of data signals than voice signals. Data
`signals are highly susceptible to beat noise which alters
`data bits rendering entire data sequences totally incom
`prehensible. The falsing of data signals may be remedied
`to some degree by the use of complex error-correction
`codes requiring complex and expensive coding devices
`at each station of a simulcast transmission system.
`For the foregoing and other shortcomings and prob
`lems, there has been a long felt need for an improved
`simulcast transmission system having transmitters at
`remote stations with more accurately controlled fre
`quencies.
`SUMMARY OF THE INVENTION
`Accordingly, it is an object of the present invention
`to provide an improved simulcast transmission system
`having phase-locked remote transmitters whose fre
`quencies are accurately maintained relative to a refer
`ence signal.
`It is a further object of the present invention to pro
`vide an improved simulcast transmission system having
`remote sites each with groups of a plurality of phase
`locked transmitters having different frequencies that are
`accurately maintained relative to a reference signal.
`It is yet a further object of the present invention to
`provide an improved simulcast transmission system
`having phase-locked remote transmitters, whose freque
`cies are not only accurately maintained relative to a
`
`50
`
`55
`
`60
`
`65
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`In FIG. 1, there is illustrated a simulcast transmission
`system for phase-locking a plurality of transmitters
`located in remote stations to a reference signal transmit
`ted from a central station. The central station includes a
`reference oscillator 100 for providing a reference signal
`of a predetermined frequency and a microwave trans
`mitter 101 for transmitting via a microwave links the
`reference signal. The remote stations include a micro
`wave receiver 102 and 103 for receiving via the micro
`wave link the reference signal transmitted from the
`central station, a signal conditioner 104 and 105 for
`conditioning the received reference signal, a phase
`locked loop (PLL) 106 to 110 responsive to the condi
`tioned reference signal for providing an intermedite
`signal and one or more transmitter blocks 110, 112 and
`111, 113 for multiplying the intermediate signal to pro
`
`Juniper Ex 1015-p. 4
`Juniper v MTel403
`
`

`
`4,188,582
`4
`3
`300. The VCXO is commonly referred to by those
`vide the transmitter signal at frequencies F1 and F2,
`respectively.
`skilled in the art as a channel element. The VCXO is of
`the type that can be frequency modulated. The modula
`The simulcast transmission system of FIG. 1 may be
`advantageously applied to the simulcast transmission
`tion may be introduced between the loop ?lter 301 and
`the VCXO 302. The VCXO is a high stability oscillator,
`system described in the aforementioned copending pa
`for example, a VCXO having a stability of two parts per
`tent application Ser. No. 815,885. The simulcast trans
`million is typical for a simulcast transmission system.
`mission system of the aforementioned application in
`In the previous example for UHF radio channels
`cludes a central station and a plurality of transmitters
`spaced at 25 KHz, in order to operate VCXO 302 at
`located at remote stations which are interconnected
`with the central station by microwave links. Messages
`14.05555 MHz for channel F1, the divider 304 is pro
`grammed to divide by 20,240. For the next channel F2,
`to be transmitted simultaneously from the remote sta
`the divider 304 is programmed to divide by 20,241 to
`tions are multiplexed over the microwave links between
`operate the VCXO at 14.05625 MHz. Thus, the divisor
`the central station and the remote stations. In simulcast
`of the divider 304 must be incremented by 1 (from
`transmission systems it is extremely important that mes
`20,240 to 20,241) to increment by 25 KHz, the channel
`sages are transmitted simultaneously and that transmit
`spacing. The divider 304 is of the programmable type
`ters assigned to the same channel are maintained at
`such that a speci?c divisor can be readily provided, for
`substantially the same exact frequency. Slight fre
`example, by a predetermined arrangement of pluggable
`quency offsets between transmitters will cause audible
`interference in the form of beat noise. According to the
`jumper wires.
`1
`A block diagram of the signal conditioner 104 and
`present invention, the central station of a simulcast
`105 of FIG. 1 is illustrated in FIG. 4. The signal condi
`system may be advantageously utilized to transmit a
`reference signal to the remote stations for phase locking
`tioner insures that a conditioned reference signal is
`always supplied to the phase-locked loops, even during
`the frequency of the transmitter signals of the remote
`brief and long interruptions of the reference signal from
`stations to the reference signal.
`the central station. Referring to FIG. 4, a reference
`Referring back to FIG. 1, the simulcast transmission
`signal from the microwave receiver is ?ltered by tuned
`system illustrated may be advantageously utilized for
`?lter 400 before application to the limiters 401 and 411.
`remote stations operating at UHF frequencies (500
`Limiter 401 is preferably designed to have a higher gain
`MHz) and remote stations operating at VHF frequen
`cies (150 MHz). For example, a suitable reference signal
`than limiter 411 in order that limiter 411 will cease to
`operate before limiter 401. This operation of the limiters
`having a frequency of 100 KHz may be provided by
`401 and 411 is provided so that an interruption in the
`reference oscillator 100. To accommodate UHF radio
`channels spaced at 25 KHz multiples, the signal condi
`reference signal can be detected from the output of
`limiter 411 before the incoming signal path to the
`tioner 104 and 105 may provide a conditioned reference
`VCXO 407 is interrupted.
`signal at 694.4444 Hz. A transmitter signal F1 at
`506.0000 MHz is achieved by operating the PLL 106
`The output of limiter 401 is applied to a phase-locked
`loop which has a forward path including phase compar
`and 108 at 14.05555 MHz and multiplying by 36 in the
`ator 402, analog switch 404, loop filter 405, sample and
`transmitter block 110 and 112. A channel F2 spaced 25
`hold circuitry 406 and VCXO 407 coupled in series, and
`KHz higher at 506.0250 MHz may be achieved by pro
`a feedback path including divider 409 coupled to the
`gramming the PLL 107 and 109 to operate at 14.05625
`VCXO 407 for providing a feedback signal to phase
`MHz.
`comparator 402. The output of the VCXO is applied to
`Utilizing the same reference signal of 100 KHz, a
`dividers 408 and 403 for providing conditioned refer
`conditioned reference signal of 1250.0000 Hz will ac
`ence signals A and B, respectively. Two conditioned
`commodate VHF radio channels spaced at 15 KHz. In
`reference signals are used in a simulcast transmission
`this case, a transmitter signal F1 at 150.0000 MHz is
`system having transmitters operating in two different
`achieved by operating the PLL 106 and 108 at 12.50000
`frequency bands, for example, UHF and VHF fre
`MHz and multiplying by 12 in the transmitter block 110
`quency bands. Each conditioned reference signal is a
`and 112. _
`common denominator of the frequencies of the trans
`In the event that a remote station is not accessible by
`mitters to which the conditioned reference signal is
`a communication path, such as a microwave link, the
`coupled.
`remote station may be organized as shown in FIG. 2. A
`50
`The output of limiter 411 is applied to activity detec
`high stability oscillator, such as an atomic clock 200, is
`tor and reset synchronizer 410. The activity detector
`utlized to provide the reference signal. For example, an
`‘ and reset synchronizer 410 controls the operation of the
`atomic clock, such as a Hewlett Packard 5062C, may be
`analog switch 404, the sample and hold circuitry 406
`used to provide a cesium-based reference signal of very
`high stability. The reference signal is then conditioned
`and the divider 409. In response to interruptions of the
`reference signal, the activity detector and reset syn
`by the signal conditioner 201 before application to the
`phase-locked loops 202 and 203. The intermediate signal
`chronizer 410 enables the‘analog switch 404 to open the
`from the phase-locked loops 202 and 203 is multiplied
`forward path to permit the VCXO 407 to free run and
`enables the sample and hold circuitry 406 to hold. In the
`by the transmitter block 204 and 205 to provide a trans
`mitter signal at frequencies F1 and F2, respectively.
`hold mode, the sample and hold circuitry 406 may store
`The phase-locked loops and transmitters of FIGS. 1
`a voltage proportional to the last received reference
`signal, which is applied to the VCXO 407 for control
`and 2 may be organized as shown in FIG. 3. The phase
`ling the frequency of the VCXO 407 during the inter
`locked loop has a forward path, including a phase com
`ruption.
`parator 300 which may be a phase-frequency compara
`The sample and hold circuitry 406 may be of any
`tor, a loop ?lter 301 and a voltage controlled crystal
`suitable type, such as, for example, a reed relay coupled
`oscillator (VCXO) 302 coupled in series, and a feedback
`to a low-leakage capacitor or the circuitry described in
`path including a divider 304 coupled to the VCXO for
`assignee’s copending application Ser. No. 875,251, enti
`providing a feedback signal to the phase comparator
`
`60
`
`25
`
`65
`
`Juniper Ex 1015-p. 5
`Juniper v MTel403
`
`

`
`5
`tled “Input Activated Frequency Synthesizer” by Don
`ald C. Ryan and ?led on Feb. 6, 1978. Once the forward
`path has been opened, the received reference signal will
`not again be recognized until it has been detected for at
`least a pre-established time interval as determined by
`the activity detector and reset synchronizer 410. Thus,
`intermittent receptions of the received reference signal
`will be ignored by the activity detector and reset syn
`chronizer 410.
`_
`Upon proper detection of the received reference
`signal by the activity detector and reset synchronizer
`410, the forward path will again be closed. In order to
`minimize the settling time of the VCXO 407 due to the
`phase difference between the newly received reference
`signal and the divider output, the activity detector and
`reset synchronizer 410 will reset the divider 409 to
`phase synchronize the output signal of the divider 409
`to the received reference signal. Thus, large phase er
`rors caused by interruptions of the reference signal will
`not result in excessively long settling times in the feed
`back path of the signal conditioner.
`A more detailed block diagram of the activity detec
`tor and reset synchronizer 410 of FIG. 4 is illustrated in
`FIG. 5. The output signal from limiter 411 is applied to
`resettablemonostable device 500, which operates as a
`missing pulse detector, as is known in the art. The Q
`output signal from the resettable monostable device 500
`is applied to resettable monostable device 501, and
`AND gate 503. The resettable monostable device 501 is
`triggered by risigg transitions of resettable monostable
`device 500. The Q output signal from resettable mono
`stable device 501 is applied to ?ip-?op 502 and AND
`gate 503. The ?ip-?op 502 is clocked by rising edges o_f
`the output signal from limiter 411 of FIG. 4. The Q
`output signal from ?ip-?op 502 is the divider reset sig
`35
`nal that is applied to divider 409 of FIG. 4. The Q out
`put signal of ?ip-?op 502 is aplied to AND gate 503.
`The output of AND gate 503 is the control signal cou
`pled to analog switch 404 and sample and hold circuitry
`406. The devices illustrated in FIG. 5 may be any of a
`number of commercially available integrated circuits.
`For example, the resettable monostable devices 500 and
`501 may be the Motorola MC14528, and AND gate 503
`a Motorola MCl4073, the ?ip-?op 502 a Motorola
`MC14013 and the analog switch 404 a Motorola
`MC14016.
`'
`Referring to the timing diagram of FIG. 6, the opera
`tion of the activity detector and reset synchronizer can
`be more clearly understood. The output signal 612 of
`the limiter 411 illustrates the receipt of the reference
`50
`signal after an interruption. When the first pulse of the
`reference signal is received, the output signal 612 of
`limiter 411 causes the output signal 610 of resettable
`monostable device 500 to transition to a high state. The
`output signal 610 of resettable monostable device 500 is
`55
`programmed to remain high for at least one full period
`of the output signal 612 of limiter 410.
`The transition of the output signal 610 of resettable
`monostable device 500 causes the output signal 611 of
`the resettable monostable device 501 to change to the
`60
`low state. At the next transition of the output signal 612
`of limiter 411, the output signal 613 of the ?ip-?op 502
`will change to a high state. The high state of the output
`signal 613 of the ?ip-?op 502 will cause the divider 409
`of FIG. 4 to be reset. If during the time period of the
`output signal 611 of resettable monostable device 501,
`the output signal 612 of limiter 411 is interrupted again,
`then the output signal 613 of the ?ip-flop 502 will re
`
`40
`
`6
`main high since resettable monostable device 501 will
`be re-triggered by the interruption. Thus, intermittent
`receipt of the reference signal after a relatively long
`interruption and occurring during the time period of
`resettable monostable device 501 will be ignored. The
`time period of resettable monostable device 501 may be
`chosen to be any suitable time period greater than twice
`the period of the reference signal.
`The control signal 614 from the AND gate 503 will
`enable the analog switch 404 to close the forward path
`to the VCXO 407 and enable the sample and hold cir
`cuitry 406 to sample when the output signal 611 of the
`resettable monostable device 501 times out and the
`output signal 613 of the flip-flop 502 changes to a low
`state. When the control signal 614 switches to the high
`state, closed-loop operation of the VCXO 407 is pro
`vided.
`A block diagram of the atomic clock 200 and signal
`conditioner 201 of FIG. 2 is illustrated in FIG. 7. Re
`dundant atomic clocks 700 and 701 are provided to
`enhance reliability. In the event that the atomic clock
`700 fails, automatic switching is provided to the other.
`Referring to FIG. 6, the atomic clocks 700 and 701 are
`coupled to dividers 702, 703 and 704, 705, respectively.
`The dividers 702 and 704 are programmed to divide by
`the same number, likewise dividers 703 and 705 are
`programmed to divide by the same number. Dividers
`702 and 703 are designated the master dividers and are
`applied to activity detector 708. Switches 706 and 707
`are provided for selecting between dividers 702 and 704
`and dividers 703 and 705, respectively. In response to an
`interruption in the output signal from either or both of
`the master dividers 702 and 703, the activity detector
`708 provides an output signal to cause the switches 706
`and 707 to switch to dividers 704 and 705, respectively.
`In order to provide the aforementioned reference
`signals for UHF and VHF radio channels, the atomic
`clocks 700 and 701 may be selected to provide a 100 '
`KHz reference signal. Dividers 702 and 704 may be
`programmed to provide a divisor of 144 for a 694.4444
`Hz conditoned reference signal A. Dividers 703 and 704
`may be programmed to provide a divisor of 80 for a
`1250.00 Hz conditioned reference signal B.
`The foregoing embodiments have been intended as
`illustrations of the principles of the present invention.
`Accordingly, other modi?cations, uses and embodi
`ments can be devised by those skilled in the art without
`departing from the spirit and scope of the principles of
`the present invention.
`What is claimed is:
`1. In a simulcast transmission system having a central
`station for controlling via communication paths the
`operation of transmitters at a plurality of remote sta
`tions, said simulcast transmission system including im
`provement for automatically phase locking the fre
`quency 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 communi
`cation 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:
`
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`(i) a ?rst phase-locked loop including a forward
`the frequency of the transmitter signals of the remote
`path having a phase comparator, an analog
`stations, comprising:
`switch, a loop ?lter, sample and hold circuitry
`(a) said central station including:
`and a voltage-controlled crystal oscillator
`( 1) an oscillator'for providing a reference signal of
`(VCXO) coupled in series, and a feedback
`a predetermined ?rst frequency; and
`path having a ?rst divider coupled to the
`(2) a transmitter for transmitting via the microwave
`VCXO for providing a feedback signal to the
`communication paths the reference signal; and
`phase comparator;
`(b) each of said remote stations including:
`(ii) a second divider coupled to the VCXO for
`(1) a receiver for receiving via the microwave
`providing the conditioned reference signal of a
`communication path the transmitted reference
`predetermined second frequency;
`signal;
`(iii) a detector for detecting the presence of the
`(2) a signal conditioner including:
`received reference signal and providing an
`(i) a ?rst phase-locked loop including a forward
`activity indication signal when the received
`path having a phase comparator, loop ?lter, an
`reference signal is present; and
`analog switch, sample and hold circuitry and a
`(iv) control means for opening the analog switch,
`voltage-controlled crystal oscillator (VCXO)
`enabling the sample and hold circuitry to
`and a feedback path having a ?rst divider
`maintain the frequency of the VCXO and
`coupled to the VCXO for providing a feed
`providing a reset signal to reset the ?rst di
`back signal to the phase comparator,
`vider to a predetermined state in the absence
`(ii) a second divider coupled to the VCXO for
`of the activity indication signal, the control
`providing a ?rst conditioned reference signal
`means closing the analog switch, enabling the
`of a predetermined second frequency;
`sample and hold circuitry to sample the output
`(iii) a ?rst monostable device for detecting the
`of the loop ?lter for controlling the frequency
`received reference signal to provide an activ
`of the VCXO, and removing the reset signal
`ity indication signal;
`from the ?rst divider in response to the pres
`(iv) a ?ip-?op responsive to the activity indica
`ence of the activity indication signal;
`tion signal and the received reference signal
`(3) a second phase-locked loop responsive to the
`for providing a reset signal for resetting the
`conditioned reference signal for providing an
`?rst divider to phase synchronize the output
`' intermediate signal of a predetermined third fre
`signal of the ?rst divider to the received refer
`quency; and
`ence signal; and the analog switch closing the
`(4) a multiplier for multiplying the intermediate
`forward path to the VCXO and the sample
`signal to provide a transmitter signal of a prede
`and hold circuitry being enabled to sample in
`termined fourth frequency.
`response to the activity indication signal;
`2. The simulcast transmission system according to
`(0) a second phase-locked loop responsive to the ?rst
`claim 1, wherein said control means is responsive to the
`conditioned reference signal ~for providing a ?rst
`activity indication signal for removing the reset signal
`intermediate signal of a predetermined third fre
`from the ?rst divider when the received reference sig
`quency; and
`nal is phase-aligned with the predetermined state of the
`(d) a ?rst multiplier for multiplying the ?rst interme
`?rst divider.
`diate signal to provide a transmitter signal of
`3. The simulcast transmission system according to
`claim 1 or 2 further including delay means interposed
`predetermined fourth frequency.
`'
`8. The simulcast transmission system according to
`between the activity detector and the control means for
`claim 7, wherein said signal conditioner includes a third
`delaying the response of the control means to the activ
`ity indication signal by a predetermined time interval.
`divider for providing a second conditioned reference
`signal of a predetermined ?fth frequency, each of said
`4. The simulcast transmission system according to
`remote stations including a third phase-locked loop
`claims 2 or 1 wherein each of said remote stations in
`cludes a plurality of second phase-locked loops and
`responsive to the ?rst conditioned reference signal for
`corresponding multipliers for providing transmitter
`providing a second intermediate signal of a predeter
`signals at corresponding predetermined frequencies.
`mined sixth frequency and a second multiplier for multi
`5. The simulcast transmission system according to
`plying the second intermediate signal to provide a trans
`mitter signal of a predetermined seventh frequency.
`claim 1, wherein said oscillator is an atomic oscillator.
`6. The simulcast transmission system according to
`9. The simulcast transmission system according to
`claim 1, further including at least one appended remote
`claim 8, wherein said signal conditioner further includes
`station having an atomic oscillator for providing a ?rst
`gating circuitry and a second monostable device, the
`output signal of the predetermined ?rst frequency, a
`second monostable device being interposed between the
`divider for dividing the ?rst output signal to provide a
`?rst monostable device and the ?ip-?op, said second
`conditioned output signal, a phase-locked loop respon
`monostable device being responsive to the activity indi
`sive to the conditioned output signal for providing a
`cation signal of the ?rst monostable device for provid
`second output signal of the predetermined second fre
`ing a pulse signal of a predetermined time period, the
`quency and a multiplier for multiplying the second
`?ip-?op being responsive to the pulse signal for provid
`output signal to provide a transmitter signal of the pre
`ing the reset signal for resetting the ?rst divider to phase
`determined third frequency.
`synchronize the output signal of the ?rst divider to the
`7. In a simulcast transmission system having a central
`received reference signal, the gating circuitry being
`station for controlling via microwave communication
`responsive to the activity indication signal, the absence
`65
`paths the operation of transmitters of a plurality of
`of the pulse signal and the absence of the reset signal for
`remote stations, said simulcast transmission system in
`enabling the analog switch to close the forward path to
`cluding improvement for automatically phase locking
`the VCXO and the sample and hold circuitry to sample.
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`(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 communi
`cation 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 ?rst phase-locked loop including a forward
`path having a phase comparator, an analog
`switch, a loop ?lter, sample and hold circuitry
`and a voltage-controlled cr