`
`US005995553A.
`
`United States Patent
`[19]
`5,995,553
`fit] Patent Number:
`
`Crandallet al. Nov. 30, 1999 [45] Date of Patent:
`
`
`
`
`54
`
`75
`
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`
`
`
`ENCODER/DECODER FOR EMERGENCY
`ALERT SYSTEM
`
`Inventors: Kenneth Crandall, Redwood City;
`Kenneth Fesler, Stanford, both of
`Calif.
`
`Assignee: TIT, Inc., Santa Clara, Calif.
`
`Appl. No.: 08/789,296
`Filed:
`Jan. 28, 1997
`
`settee HO4D 27/10
`TInt. CL
`
`.. 375/272; 455/404; 455/521
`US. Cl...
`
`wee 375/219, 222,
`Field of Search ou...
`242;
`375/272, 303, 334,
`340/870.09, 901,
`870, 945; 329/300, 315; 332/100, 118,
`117; 348/14; 455/404, 521, 527
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,692,742
`
`4,956,866
`5,038,402
`5,045,839
`5,148,153
`5,241,689
`5,420,888
`5,533,062
`
`
`9/1987 Raizenet al.
`...
`wee 340/539
`10/1989 Fisch etal.
`.
`. 340/825.44
`
`9/1990 Bernstein elal.
`TOA/274
`
`8/1991 Robbins
`455/3
`9/1991 Ellis et al.
`340/539
`
`/1992 Haymond .
`340/461
`8/1993 Schwedetal.
`455/541
`
`5/1995 Davis etal.
`375/334
`7/1996 T.iberti, Ir. et al
`375/334
`
`10/1996 Takahisa .........
`wee 455/66
`
`OTHER PUBLICATIONS
`
`Article by Frederick M. Baumgartner entitled Upgrading
`‘The Emergency Broadcast System: published during the
`year 1993,
`Article by TTT, Inc. and submitted by I'rederick M. Baum-
`gartner,entitled “EmergencyInformation System”circulated
`on Dec. 11, 1992 at a Federal Communication Conference in
`Washington, D.C.
`Primary Examiner—Wellington Chin
`Assistant Examiner—Congvan Tran
`Altorney, Agent, or Firm—Jack M. Wiseman
`[57]
`ABSTRACT
`An encoder/decoder for an emergencyalert system to enable
`broadcasters to reecive, slore, re-broadcast and originale
`emergencyalert messages. Multiple emergency alert signals
`are received by the encoder/decoder. A digital signal pro-
`cessor of the encoder/decoder scans the reception of the
`multiple emergency alert messages to determine the pres-
`ence of an incoming emergency alert signal.
`‘The digital
`signal processor provides digital implementation of a fre-
`quency shift key modulation and a frequency shift key
`demodulation to cneade and decode emergency alert mes-
`sages. Additionally, the digital signal processor functions as
`a central processing unit to control input/output ports over a
`digital signal processor bus for performing all encoding and
`decoding functions and to control all encoding and decoding
`functions.
`
`21 Claims, 8 Drawing Sheets
`
`
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`
`1 of 16
`1 of 16
`
`

`

`U.S. Patent
`
`Nov.30, 1999
`
`Sheet 1 of 8
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`5,995,553
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`U.S. Patent
`
`Nov.30, 1999
`
`Sheet 2 of 8
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`5,995,553
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`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 3 of 8
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`5,995,553
`
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`4 of 16
`4 of 16
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`

`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 4 of 8
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`5,995,553
`
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`

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`U.S. Patent
`
`Nov.30, 1999
`
`Sheet 5 of 8
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`5,995,553
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`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 6 of 8
`
`5,995,553
`
`Fam
`
`
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` |“9600 SEC.
`ELAPSED ?
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`STORE DIGITIZED
`AUDIO INPUT SAMPLE
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`7 of 16
`7 of 16
`
`

`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 7 of 8
`
`5,995,553
`
`
`
`RECEIVE
`WEEKLY OR
`
`MONTHLY TEST
`?
`
`RX TIME = CURRENT TIME+8 DAYS
`
`NO
`
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`
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`
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`
`RECEIVED FOR 8 DAYS”
`
`
`
`8 of 16
`8 of 16
`
`

`

`U.S. Patent
`
`Nov.30, 1999
`
`Sheet 8 of 8
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`9 of 16
`9 of 16
`
`
`
`
`

`

`5,995,553
`
`1
`ENCODER/DECODER FOR EMERGENCY
`ALERT SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`to encoder/
`invention relates in general
`The present
`decoders, and, more particularly, to an encoder/decoder for
`an emergencyalert system.
`The patent to Ganzer et al., US. Pat. No. 5,121,430,
`issued on Jun. 9, 1992, for Siorm Alert For Emergencies,
`discloses an emergency alert system. The emergencyalert
`system includes a code generator whichis part of a broadcast
`transmission system. The code generator produces a com-
`posite code signal. One component of the composite code
`signal designates a geographical area [or receiving a mes-
`sage. Another component of the composite code signal
`designates the alert message for the designated geographical
`area. The composite code signal
`is encrypted and the
`encrypted composite code signal modulates an audio carrier
`by frequencyshift keying. Remote receivers are tuned to the
`broadcast
`transmittcr. The receivers demodulate the
`encrypted composite code signal and recovers therefrom the
`composite signal. A data comparison circuit within the
`Teceivers compares the user location code with the desig-
`nated geographical location cade. If a match is detected a
`selected numberof times over a predetermined time period,
`the receivers in which the match is detected will activate an
`alarm and the alert message is reproduced by the receiver.
`The broadcast transmitter may be a television transmitter
`and the remote receivers maybetelevision receiver circuitry.
`In the patent to Permut et al., U.S. Pat. No. 4,155,042,
`issued on May 15, 1979, for Disaster Alert System, there is
`disclosed a central alert station. The central alert station
`includes a code selector and transmits coded radio frequency
`activation signals specifying the geographical area. The
`central alcrt station also transmits audio signals containing
`an audio message. Simultaneous transmission of the coded
`activation signal and the audio signal are possible by mul-
`tiplexing both signals on the same [requency by employing
`a multiplexer. A plurality of radio frequency receivers are
`remotely located. The output of each ofthe radio frequency
`receivers is supplied to a decoder, which analyzes the coded
`radio frequency activation signal. Detection of a coded
`activation signal by the decoder results in the activation of
`powercircuits. Each decoder is coupled to its associated
`radio frequency receiver and enables user entry of the
`location code corresponding to the geographical area of the
`associated receiver. Activation of the power circuits results
`in the operation of an audible alarm, a display of a visible
`alarm, reproduction of an audio message, and the activation
`of desired auxiliary units.
`The patent to Giallanza et al., U.S. Pat. No. 4,383,257,
`issued on May 10, 1983, for Message Communication
`System With Message Storage, discloses a transmission
`system. The transmission system developes a binary
`encoded data train having a header followed by a message.
`The data train is applied to a carrier frequency to modulate
`the carrier using frequency shift key techniques. The header
`uses synchronizing signals, one or more addresssignals, and
`a message. One or more reccivers reccive the message in
`response to an address signal in the header. The digital data
`is converted into audio signals for modulating the transmit-
`ted signal by frequency modulation. A receiver/demodulator
`detects the binary encoded data train and demodulates the
`carricr modulated by the audio frequencics into the corre-
`sponding sequence of binarylogic levels. The demodulated
`digital data is then applied to a bit synchronizer that syn-
`
`10
`
`boon
`
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`
`60
`
`65
`
`2
`chronizes the internal clocks of the receiver to the incoming
`data train so that each of the binary data bits can be sampled
`and applied to a decoder. The decoder stores the message
`prior to display of the message on a visual alphanumeric
`display.
`In the patent to Bernard et al., U.S. Pat. No. 4,956,875,
`issued on Sep. 11, 1990, for Emergency Radio Alerting And
`Message Transmitting System Directable To Selected
`Classes And Numbers OF Receivers, there is disclosed an
`emergency radio alerting and warning system. The emer-
`gency radio alerting and warning system includes a fre-
`quency modulated transmitter. The broadcast signal from the
`frequency modulated transmitter uses an encoder Lo provide
`a code to enable broadcasting to be made to particular
`reecivers in a sclectcd gcographical location. The broadcast
`signal is a composite signal that also includes sound mes-
`sages and audible alarms. Frequency modulated receivers
`are receptive, bul inactive, until the specific encoded geo-
`graphical signal at
`frequency modulated receivers is
`received. Upon detecting the specific encoded geographical
`signal, the activated frequency modulated receivers activate
`an audible alarm followed by the alert message.
`The patent to Rush, No. U-S. Pat. No. 5,030,948, issued
`on Jul. 9, 1991,
`for Multiple Characteristic Sensitive
`Addressing Scheme For A Multiple Receiver Data Network,
`discloses a data transmission network. The data transmission
`network includes a transmitter for transmitting messages via
`a radio wave type communications medium, such as a
`sub-audible carrier or a frequency modulated broadcast band
`or an ultra high frequency television spectrum for incorpo-
`ration into existing television transmission. The data trans-
`mission is a composite signal that includes a code compo-
`nent and a message component. Receivers compare the code
`component. Should the code of the receiver match the
`transmitted code,
`then the message is stored. The stored
`message maybe outputted by altcrnative apparatus includ-
`ing a circuit capable of generating audio from digital data.
`In anarticle circulated on Apr. 18, 1993, by Frederick M.
`Baumgartner of TFT,Inc. of Santa Clara, Calif., at an NAB
`Convention in Las Vegas, Nev., there is disclosed an emer-
`gency broadcast system in which a microprocessor scans
`audio and data sources for emergency information. The
`emergency broadcast system employs a header containing
`location and emergency alert information. The emergency
`alert information is decoded by a receiver system that scans
`between several
`information sources. Decoders scan or
`monitor looking for the emergency information source pre-
`amble and data. Decoders decode the original emergency
`information source header, data and end of message and then
`regenerate the frequency shift keying of the emergency
`information system signal. The sources of emergency
`information, which provide audio signal input arc connected
`to an audio bus. A voice storage is provided for review or
`rebroadcast of emergency information. The emergency
`information system utilizes all electronic media, including
`broadcast television, radio, cable delivered services, satellite
`services, data scrviccs, and government andprivate warning
`services.
`
`SUMMARYOF THE INVENTION
`
`invention is to provide an
`An object of the present
`encoder/decoder for an emergencyalert system at a rela-
`tively low cost with relatively casy operation and installa-
`tion.
`Another object of the present invention is to provide an
`encoder/decoder for an emergency alert system that has
`greater accuracyin the detection of additional waveforms.
`
`10 of 16
`10 of 16
`
`

`

`5,995,553
`
`4
`audio channel connectors 16 and 17 are balanced audio
`amplifiers 20 and 21. Connected to the output of the audio
`amplifiers 20 and 21 are suitable audio or analog switches
`25-27. The audio switches 25-27 route the output signals
`from the balanced audio amplifiers 20 and 21 to a coder/
`decoder (codec) 30.
`The codec 30 converts audiosignals to digital signals and
`converts digital signals to audio signals. In addition thereto,
`the codec 30 converts digital data signals generated by a
`digital signal processor 35 to audio signals. The codec 30 is
`a combination of a coder and decoder operating in different
`directions oftransmission within the encoder/decoder 10. In
`the exemplary embodiment, the codec 30 is of the type
`manufactured by Texas Instruments Corporation of Dallas,
`Tex., as the TCM320AC37N.
`The audio switches 25-27 also route the output of the
`audio amplifiers 20 and 21 to a volume control 31 and a
`digital voice recorder 32. The output of the volume control
`31 is applied to a speaker driver 36, which is connected to
`a front panel speaker 37 of the encoder/decoder 10. The
`volume control 31 is adjusted by software to regulate the
`audio level of the panel speaker 37. In addition thereto, the
`volume control 31 also adjusts the output of the audio
`amplifier 40 to regulate the audio level of emergency alert
`signals applied to a local transmission system, not shown,
`over a conductor 41. The volume control 31 is manufactured
`and sold by Maxim Integrated Products of Sunnyvale, Calif.,
`as the MAX532B095. Should the alert message be verified
`by the digital signal processor 35 for re-transmission over
`the conductor 41, it will have a new station identification
`code inserted therein and it will include a two-tone attention
`signal, a recorded voice message, and an cnd of message
`signal. Each header code message and each end of message
`code will be preceded by a digital preamble code of the
`digilal emergency alert system header 15.
`Thedigital voice message recorder 32 digitizes and stores
`voice messages for playback or for re-broadcast. It is a
`sampling analog-to-digital converter and a digital-to-analog
`converter that converts incoming voice messages Lo digital
`data and stores the digital data in voice memories thereof at
`sclect memorylocations for voice storage. In the exemplary
`embodiment, the last incoming audio message, up to two
`minutes, is available for the operator’s immediate review.
`The operator can decide whether to forward the last message
`received after review of the header 15 and the voice mes-
`sage. The digital voice message recorder 32 allows auto-
`matic forwarding of the voice message without using an
`external recording device.
`To play back a message, the digital voice recorder 32
`retrieves digital data from the voice memories thereof and
`converts the data back into its original analog form. Audio
`signal buffering, gain and automatic level control are pro-
`vided by the digital voice recorder 32. Okidata Corp. of
`Milpitas, Calif., manufactures and sells the digital voice
`recorder 32 as manufacturing part number MSM 6389 QFP,
`which stores the digital data, and as manufacturing part
`number MSM 6389 QFJ, which is the controller for the
`digital voice recoder 32.
`The digital signal processor 35, which is manufactured
`and sold by Texas Instruments Corporation of Dallas, Tex.,
`as the TMS320C26, scans the multiple audio input signals
`applied to the channel connectors 16 and 17 by way of the
`audio switches 25-27, cadec 30 and a conductor 42 to
`determine the presence of an incoming signal representing
`an emergencyalert message. In addition thereto, the digital
`signal processor 35 provides a digital implementation of a
`
`3
`the present invention is to provide an
`Another object of
`encoder/decoder for an emergency alert system that is more
`tolerant to distortions in the reception of audio input signals.
`Another object of
`the present invention is to provide an
`encoder/decoder for an emergency alert system that has
`improved signal
`to noise ratio performance and greater
`tolerance to phase distortion.
`Another abject of the present invention is to provide an
`encoder/decoder for an cmergency alert system in which
`there is improved selectivity in the detection of incoming
`audio signals.
`Another abject of the present invention is to provide an
`encoder/decoder for an emergencyalert system in which test
`reminder messages are displayed when the encoder/decoder
`has not
`transmitted or received test messages within a
`prescribed period of
`time.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`
`
`
`
`FIG. 1 is a diagrammaticillustration of a web structure for
`an emergencyinformation superhighway.
`FIG, 2 is a diagrammatic illustration of a timing diagram
`of a header and message encoded and decoded bythe
`encoder/decoder of the present invention.
`FIG. 3 is a block diagram of the encoder/decoder embody-
`ing the present invention.
`FIG. 4 is a block diagramof a delay and multiplier for a
`frequency shilt key demodulator employed in a digital signal
`processor of the encoder/decoder shown in FIG.3.
`TIG. 5 is a flow chart for the delay and multiplier for the
`frequency shift key demodulator employed in the digital
`signal processor of the encoder/decoder shown in FIG. 3.
`FIG. 6 is a flowchart of the weekly/monthly test reminder
`of the digital signal processor of the encoder/decoder shown
`in FIG.3.
`
`FIG. 7 is a front elevation viewof the front panel for the
`encoder/decoder embodying the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`boon
`
`woon
`
`The encoder/decoder 10 of the present invention enables
`broadcasters to receive, store, re-broadcast and originate
`emergency alert messages. When an agency, such as the
`National Weather Service or the Emergency Operations
`Center, issues an alert message, it transmits a digital emer-
`gencyalert header and a voice message throughthe encoder/
`decoder of the present invention to a local AM, FM or
`television station. The encoder/decoder 10 is located at the
`site of the local AM, FM ortelevision station employing the
`same. The local AM, I'M ortelevision station,
`in tum,
`re-broadcasts the voice message to remotely located AM,
`FM or television receivers. By way of example, a web
`structure for emergencyalert system information superhigh-
`way is diagrammatically illustrated in FIG. 1 wherein
`agencies, such as the Emergency Operating Centers,
`National Weather Service and other similar agencies,origi-
`nate alert messages and transmit a digital emergency alert
`system header 15 (FIG. 2) and a voice message to a local
`AM,I'M,ortelevision station, which, in turn, broadcasts the
`voice message to remotely located receivers designated for
`receiving the voice messages, such as receivers located in a
`designated geographical area.
`Multiple emergency alert signals from respective emer-
`gencyalert systems are applied respectively to audio chan-
`nel connectors 16 and 17. Interfaced, respectively, with the
`
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`

`5,995,553
`
`5
`frequency shift key modulator and a frequencyshift key
`demodulator to encode and decode emergency alert mes-
`sages. The digital signal processor 35 functions as a central
`processing unit to control input/outputports 45 overa digital
`signal processor bus 46 for sclccting the switching operation
`of the audio switches 25-27; and to adjust
`the volume
`control 31 for regulating the audio level of the panel speaker
`37 and the audio level of the emergency alert message to a
`broadcast transmission system, not shown. Thus, the digital
`signal processor 35 performs all encoding and decoding
`functions and controls all input/output activity.
`A field programmable gate array 50, which is manufac-
`tured and sold by Xilinx, Inc. of San Jose, Calif, as the
`XC3042,
`is operatively controlled by the digital signal
`processor 35 through the digital signal processing bus 46 to
`generate all internal timing signals and to perform intcrnal
`digital signal routing. Connected to the ficld programmable
`gate array 50 is a bi-directional RS-232 interface 51, which
`provide ASCII data input of emergency alert system mes-
`sages. In the exemplary embodiment, the rate for the data
`output is 1200 baud. In the exemplary embodiment, a 60 Hz
`clock reference is applied to the field programmable gate
`array 35 from a suitable source, not shown. Also applied to
`the field programmable gate array circuit 50 is a printer/
`speaker inhibit 52. ‘Vhe printer/speaker inhibit 52 inhibits or
`mutes a printer 53 and the speaker 37 when desired by
`closing a normally opened switch or relay contacis, not
`shown.
`Arcal-time clock circuit 55 underthe controlofthe digital
`signal processor 35 over the digital signal processor bus 46
`maintains a calendar and time of day. The real-time clock
`circuit 55 is manufactured and sold by Dallas Semiconduc-
`tor of Dallas, Tex., as the DS14285. The output of the
`real-time clock circuit 55 is connected to a set-up memory
`or system random access memory 62, which is used for
`temporarydata storage and calculations as well as long term
`storage of setup information. The system random access
`memory 62 communicates with the digital signal processor
`35 through the digital signal processor bus 46. ‘The event and
`location data of the header 15 (FIG. 2) is compared with the
`data stored in the system random access memorycircuit 62
`by the signal digital processor 35 for validation to determine
`whether the incoming message should be re-transmitted
`through the encoder/decoder 10.
`A system read-only program memory 54 stores the
`Instructions [or the operation of the encoder/decoder 10 and
`the encoding and decoding software for the digital signal
`processor 35. The system read-only program memory 54 is
`connected to the digital signal processor 35 through the
`digital signal processor bus 46. The operating system
`sattware, the encoding software and the decoding software
`are stored in the system read-only program memory 54. A
`reset circuit and watchdog timer 60 provides power-on and
`default/time-outreset for the digital signal processor 35 and
`the central processing umit thereo!.
`The digital signal processor 35 provides output message
`information for the printer 53 through the digital signal
`processor bus 46 and a printer interface 61. The routing of
`data to the printer 53 is controlled by the field programmable
`gate array 50 and the input/output ports 45 under instruc-
`tions fromthe digital signal processor 35. The printer 53, in
`the exemplary embodiment,
`is an ASCII
`impact printer,
`which has 24 columns to record emergencyalert signal
`messages reccived and transmitted to the encoder/decoder
`10. The digital header data and the incoming message are
`printed out by the printer 53.
`In addition to the foregoing, the digital signal processor
`35 controls the current output status of a liquid crystal
`
`
`
`wn
`
`10
`
`65
`
`6
`display 65. The field programmable gate array 50, upon
`instructions from the digital signal processor 35, controls the
`routing of data to the liquid crystal display 65 through the
`input/output ports 45. It is the liquid crystal display 65 that
`scrolls incoming messages provided bythe digital signal
`processor 35. The scrolling of incoming messages accom-
`modates long messages. Further, the liquid crystal display 65
`also displays encoder functions, message forwarding and
`configuration setups. The digital header 15 with the incom-
`ing message is decoded and transmitted bythe digital signal
`processor 35 to the liquid crystal display 65 and the printer
`53 through the digital signal processor bus 46. ‘he data and
`message information displayed in the liquid crystal display
`65 is printed oul on the printer 53.
`In the exemplary
`embodiment,
`the liquid crystal display 65 is a large
`character, backlighted display with contrast and backlayer
`controlled by software. Suitable liquid crystal displays are
`manufactured and sold by T-tech Corporation of Alamosa,
`Colo., as the TLCD1616DLGY and by Data International
`Co. of Taipei, Taiwan, as the VD-1610-1SFDLY.
`The digital signal processor 35 is programmedto differ-
`entiate between incoming frequency shift key frequencies in
`which emergencyalert system data is encoded. The fre-
`quencyshill key [requencies, in which emergency alert dala
`system data is encoded, are converted by the digital signal
`processor 35 to digital data by frequency shift key demodu-
`ation.
`In the exemplary embodiment,
`the instantaneous
`frequency of each frequency shift key frequencyis shifted
`between a mark frequency of 2083.3 Hz and a space
`requency of 1562.5 Hz, which correspondsto the digital
`values of 0 and 1 of the ASCII data being transmitted to the
`audio channel connectors 16 and 17.
`The digital signal processor 35 performs frequency shift
`ey modulation and frequency shift key demodulation lor
`he encoder/decoder 10. In FIG. 4,there is illustrated a delay
`and multiplicr 70 for the frequencyshift key demodulation
`performed bythe digital signal processor 35. The frequency
`shift key demodulation performed by the digital signal
`processor 35 improvesthe signal Lo noise ratio performance
`of the encoder/decoder 10 by including information from
`additional points on the input waveform spaced to achieve a
`180 degree mark/space phase difference between the mark
`requency of 2083.3 Hz and the space frequency of 1562.5
`Hz. This phase difference improves the mark/space decision
`process. The frequency shift key demodulation performed
`by the digital signal processor 35 increases the tolerance of
`hase distortion performance.
`Toward this end,
`the delay and multiplier 70 for the
`requency shift key demodulation performed by the digital
`signal processor 35 comprises a multiplier 71. One input of
`he multiplier 71 has applied thereto an audio input signal
`originating from an audio input channel connector, such as
`he audio input channel connector 16. Another input of the
`multiplier 71 has applied thereto the audio input signal
`onginaling from the same audio inpul channel connector
`hrough a time delay 72. In the exemplary embodiment, the
`ime delay is 9/9600 sccond. The same audio inputsignal is
`applied to one input of a multiplier 73 through the delay 72
`and a delay 74. In the exemplary embodiment, the delay 74
`is 9/9600 second. The product of the multiplier 71 and the
`product of the multiplicr 73 are added by an adder 75. The
`output of the adder 75 is applied as data output through a low
`pass filter 76 to enable the digital signal processor 35 to
`make improved mark/space decisions. The additional delay
`and multiplier 70 maximizes the difference between mark
`and space to improve the decision process of the digital
`signal processor 35. A flowchart for the delay and multiplier
`70 is shownin FIG.5.
`
`
`
`12 of 16
`12 of 16
`
`

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`5,995,553
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`boon
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`7
`By virtue of the additional delay and multiplier 70, the
`encoder/decoder 10 is more tolerant to distortions in the
`reception of audio input signals and there is greater selec-
`tivity in the selection of incoming audio signals. Thus, the
`encoder/decoder 10 has greater accuracy in the detection of
`additional waveforms.
`The encoder/decoder 10 is activated by the emergency
`alert signals. In the exemplary embodiment, the emergency
`alert signals include a preamble and header codes; a two-
`tone attention signal; a voice message; and the preamble and
`end of message codes (FIG, 2). The emergencyalert signals
`are applied to an audio channel connector, such as the audio
`channel connectors 16 and 17, respectively. The preamble
`and header codes, modulated by audio frequency shift
`keying, are transmitted to respective audio channel connec-
`tors 16 and 17. In the exemplary embodiment, the audio
`frequency shift keying of the preamble and header codes is
`at
`a
`rate of 520.83 bits per second.
`In the exemplary
`embodiment, the mark frequency of the audio frequency
`shift keying is 2083.3 Hz and the space frequency is 1562.5
`Hz. The mark and space times,
`in the exemplary
`embodiment, are 1.92 milliseconds.
`In the exemplary
`embodiment, the characters are ASCII 7-bit characters, as
`defined in ANSI X3.4-1977, ending with an eighth null bit
`(either 0 or 1) to constitute a full eigth-bit byte. The attention
`signal
`is transmitted after the header code, and,
`in the
`exemplary embodiment, is made up of two simultaneous
`tones. In the exemplary embodiment, the fundamental fre-
`quencies of the attention signal are 853 Hz and 960 Hz.
`The emergency alert signal header 15 is digitally coded 3
`and encodes the following signals: preamble code, origina-
`tor identification code, event code,
`location code, event
`duration, time stamp, and station identification. ‘The origi-
`nator identification code indicates who originally initiated
`the activation of the emergencyalert system. The event code
`indicates the nature of the emergency alert message. The
`location code indicates the geographic area designated to
`teceive the emergency alert message.
`‘The event duration
`code indicates the valid time period for the alert message.
`The time stamp code sets forth the day of the year and the
`time of the day that the message wasinitially released by the
`originating agency. Lastly, the station identification is the
`call sign or other station identification of the broadcast
`station or agency office transmitting or re-transmitting the
`emergencyalert message. In the exemplary embodiment, for
`reliability the header 15 is repeated three times and the
`header preamble code of the header 15 is repeated before
`each of the three end of message codes.
`The digital header 15 in the incoming emergencyalert
`message is decoded and translated by the digital signal
`processor 35 and then displayed on the liquid crystal display
`65 and printed out on the printer 53. The digital signal
`processor 35 compares the event code and the location code
`of the digital header 15 with data stored in the system
`random access memory 62 for validation to determine
`whether the emergencyalert signal and the voice message
`should be re-transmitted over the audio output conductor41.
`Should the event code and the location code matchthe data
`stored in the system random access memory 62, or be
`validated, then the digital signal processor 35 inserts the
`stored station identification code and re-transmits the header
`code, the two-tone attention signal, the voice message and
`an end of message signal through the audio amplifier 41 and
`over the audio output conductor 41. The audio switches
`25-27 are selectively activated bythe digital signal proces-
`sor 35 via the input/output ports 45 to switch the encoder/
`decoder 10 between the decoding and translating mode and
`
`woon
`
`4n
`
`8
`the re-transmitting mode over the audio output conductor
`41. A bidirectional RS 232 port 85' provides for data output.
`In the exemplary embodiment, the data is at 1200 baud.
`Additionally,
`the input/output ports 45 route data to a
`four-port communication expander 78, which provides com-
`munication links to selected equipment, such as a character
`generator or a password computer controller. Further, the
`input/output ports 45 route data ta the audio switches 25-27
`and an on-air relay driver 81 and an alcrt relay driver 82 to
`control external devices. The on-air relay has normally
`opened contacts and the relay contacts close whena valid
`emergency alerl signal
`is transmitted from the encoder/
`decoder 10 to illuminate an on-air light (FIG. 7). The alert
`relay has normally opened contacts and the relay contacts
`close when a valid emergencyalert signal is received from
`the encoder/decoder 10 to illuminate an alert light (FIG. 7).
`An RS485interface port 83 provides a communication path
`for external remote control/status module 56 between the
`digital signal bus 46 and the remote control/status module
`56. The external remote control/status module 56 is a
`remotely located transceiver that controls the status of the
`encoder/decoder 10 and receives messages from the digital
`signal processor 35. The input/output ports 45 route control
`signals to the audio switches 25-27, the volume control 31,
`and the codec 30 over conductors 85.
`
`In the exemplary embodiment, a 48-bit serial-to-parallel
`shift register, not shown,is