CA1191943A - Receiver for a tv sound transmission system - Google Patents

Abstract

A B S T R A C T

A television signal audio transmission system comprises transmission means for developing first and second stereophonic-ally related audio signals and means for developing a third audio signal. The transmission means further includes circuitry for developing a composite baseband signal having a first component comprising the sum of the first and second audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a 2fH
subcarrier with the difference between the first and second audio signals, a third component comprising a pilot signal having a frequency fH and a fourth component. comprising a 4fH
subcarrier signal frequency modulated according to the third audio signal, where fH represents the horizontal scanning line frequency. The composite baseband signal may include a fifth component comprising an approximately 5.5fH subcarrier signal frequency modulated in accordance with a first information signal and a sixth component comprising an approximately 6.5fH sub-carrier signal frequency modulated in accordance with a second information signal. In an alternate embodiment, the fourth and fifth components are replaced by a 5fH subcarrier signal frequency modulated according to the third audio signal. The composite baseband signal is used to frequency modulate a transmitted main audio RF carrier, the transmitted signal being detected by receiving circuits for reproducing the stereophonic audio signals, the third audio signal and the first and second information signals.

Description

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Tlle present :inverltion .re]ates qelleral:ly to a new and improved televi.s:i.on aucllo transmission system and is particularly di:rected to apparatus and methods for receiving an audio signal which is compatible with existing television audio receivinq circuits and which comprises a series of componen-ts, including stereophonic components, efEicien-tly utilizing -the audio bandwidth of a broadcas-t television channel.
Thi.s applica-tion is a divisional application of applicant's Canadian application Serial No. 380,579, fi.led June 25, 1981.
Under present television broadcasting standards, a band of frequencies approximately 80 KEIz wide is designated within each 6 ~Hz television channel for the transmission of the audio component of a television signal. Within this band of frequencies, an RF main audio carrier signal is frequency modulated by an audio baseband signal for producing a monaural audio -transmission signal. I~he transmitted monoaural audio signal is received by a television receiver which converts the RF audio carrier signal -to a signal having a frequency centered at ~u5 MHz. The converted ~.5 MHz sound carrier is then processed by an FM detector to reproduce the monaural audio signal which was used -to frequency modulate the RF audio carrier a-t the transmitter. In -this regard, it has been recognized that the audio bandwidth of a television channel has heretofore been largely underutilized whereby the opportuni.ty to transm:Lt a subs-tantial amount of informati.on in addition to the conventi.onal monaural signal over this ~requency band has not been ta~en advantage of.
It is accordincJ]y a basic object oE the present invention to provide a system more fully exercising the audio bandwidth of a conventional televi.sion channel and which i.s compatible wi-th present-day televisi.on receivers. More particularly, it is an '~
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object of t~e ;)reserlt invelltioll to provide apparatus for trans-mitting and receiving informatiorl over the audio bandwidth of a television charlnel which information includes stereophonic sound components as well as a number of additiollal audio informatio components.
The -transmission of stereophonic audio signals has been popular in radio broadcasting for some time, the basic l`CC
approved sys-tem being di~closed in U. S. Patent No. 3,257,511 to R. Adler et al. In th:is system, the arithmetic sum of left (L) and right (~) audio source signals (L-tR), comrnonly referred to as the main channel modulation, i5 used to directly frequency ' modulate the I~ carrier signal. The difference be-tween the left and right stereophonically related sic3nals (L-R) is used to amplitude modulate a 38 K~lz subcarrier signal in a suppressed carrier fashion with the resultan-t double-sideband signal being impressed as frequency modulation on the radia-ted RF carrier. In addition, a pilot subcarrier signal of 19 KHz is transmitted for synchronization of the FM receiver. The FM receiver extracts the 19 KHz pLlot subcarrier, doubles its requency, and applies the resulting 38 KHz signal to a synchronous detector where the (L-R) diference signal is recovered from the amplitude modulated 38 KHz stereophonic subcarrier. The recovered (L-R) modulation is then suitably matrixed with the (L-~R) main channel modulation in order to recover the original left and right stereophonic signals.
The foregoing stereophonic radio broadcasting system often also includes an SCA componen-t which allows broadcasters to provide a subscription background music service. The SCA
component comprises a 67 K~lz subcarrier ~requency modulated by the baclcground channel program, the requency modulated D~

subcarrier L~eill(3 ~Ise~ to frequel-lcy modlJlLIte the main RF
carrier sic3nal toget}?er with the stereophonic mod~lation.
~ Various sysl:erlls and apparatus have been proposed for the t~ansmission of stereop}lonic sound together with a con-vent:i~nal television picture transmission. These systems normally utilize the radio broadcasting stereopllonic trans-mission techniques discussed above but with, in most cases, differen-t subcarrier frequencies selected for their compati-bility with the transmitted video signal. One such prior art system is disclosed in U. S. Patent No. 4,04a,654 to Wegner.
This patent discloses a transmission system in which a composite baseband signal identical to that ernployed in IM stereophonic radio broadcasting is employed to frequency modulate the main sound carrier of a television transmission signal. Thus, the proposed composite baseband signal includes an (L-~R~ main channel component, an amplitude modulated double-sideband suppressed-carrier 38 KHz subcarrier (L-R) component and a 19 K~lz pilot component. In another embodiment, the use of a subcarrier signal having a frequency equal to 5/4 of the horizontal scanning line frequency (fll) characterizing the trans-mitted video signal is proposed in lieu of the 33 Kllz tL-R) channel subcarrier to reduce interference from the video component of -the television signal.
Another system, which was proposed in U. S. Patent No. 3,099,707 to R. B. Dome, also employed the conventional stereophonic radio broadcast:ing system but wlth an (L-R) chanrlel slbcarrier equal to 1.5 fll and a pilot signal eq-lal to

2.5 f~. These frequellcies were selected to minilllize the effect of the video compollerlts of the television signal appearing in 3n the recovered sidebarlds of the (L-R) channel signal.

U. S. Paten~ 3,0~16,329 to Reeso.r discloses yet another sirnilar system in which the comyosite baseband signa.l used to ~requency modulal,e the main sound carrier includes only the main channel (I.+~) component and tlle upper sidebands of t}le (L-~) cllannel signal amplitude modu].ated on a subcarrier having a frequency of 2fl~. Other prior art systems for stereophonic television sound transmission have proposed the use of Erequency modulated subcarriers for the (L-R) stereo channel typically centered at 2fl~ although a center frequency of 1.5 f~.] has also been proposed.
As previously mentioned, in adclition -to transmitting s-tereophonic sound components on the main aural carrier of a transmitted television signal, it is also desirable to transmit additional information -thereby more comple-tely exercising the available audio bandwidth wi-thin a television channel. For example, the transmission of a second language audio signal would enable a viewer to selectively operate a television receiver for reproducing the audio signals associa~ed with the transmitted ste.reophonic information, or alternatively, the audio signals associated with the transrnitted second language information.
Other exarnples of such additional information include ENG
electronic news gathering) signals and telemetry signals, both of which television broadcasters employ for their own private use. ENG signals are employed to provide a direct communications link between a broadcaster and his station's remote camera crews Eor real-time news reporting while -telemetry signals consist of F`CC required remote read-outs from unattended trans-mitter locations to a control location.

One prior art ~-)ro"osal tor providing a second ]anguclge capability in connection with a transmitted television sigrlal is discloc;ed in previously merltioned U. S. Patent No. 4,048,654 to Wegner in which the two channels of a stereophonic-like signal are employed. In particular, the (L-~R) main channel signal is used to transmit a first language audio signal and the (L-R) stereo channel signal is used to' transmit a second language audio signal. U. S. Patent No. 3,221,098 to Feldrnan discloses a -transmission system allowing for the simultaneous broadcast of a single television program having up to four or more different language soundtracks by forrning a composite baseband signal consisting of four or more different subcarrier signals each amplitude modulated with a different language audio signal, the composite baseband signal being used to frequency modulate the main RF audio carrier.
Yet another proposed second language system uses a frequency modulated subcarrier baseband signal centered at 2f}l for both stereophonic sound transmission ancd for second language trans-mission. A pilot signal, modulated with one of two different frequencies, is used to indicate which service is being broadcast.
The foregoing systems and techniques for transmitting different audio signals in conjunction with a standard television transmission have not been adopted in the U. S. for a nurnber oE
reasons including, in certain cases, poor performance and, in others, incompatibility with U. S. television transmission standards. The systern of the present invention, on the other hand, cornprises a audio transmission system which is fully compatible with U. S. television broadcasting standards and is capable of providing high-fidelity stereophonic sound trans-missiorls together with a high quality second language service.

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The system is :Further characterized in that ENG
and telemetry si.c3nals are also conveniently accommodated wi.thin -the audio bandwidth of a teLevision channel.
The present inven-tion relates to a receiver for a television signal transmission system characterized by a transmi-t-ted aural signa]. compr:ising a main carrier signal frequency modulated ln accordance with a composite modu:Lation function having a flrst cornponen-t comprising the sum of first and second stereophonically related audi.o signals a second component comprising a double sideband suppressed carrier signal formed by ampli-tude modulating a first subcarrier having a frequency 2E~I in accordance with the difference between the stereophonica].ly related audio signals a third component comprising a second subcarrier having a frequency equal to an integral multiple greater than three times fll frequency modulated in accordance with a third audio signal and a fourth component comprising a pilot signal having a frequency f~l where f~l is the horizontal scanning line frequency associated with the hori.zontal sync signal of a transmitted te].evision signal. The receiver comprises: input means responsive to a transmi-tted television signal for deriving the composite modulation function; means responsive to the derived composite modulation Eunctiorl for regenerating the first subcarrier signal in a form phase and frequency locked to the second harmonic oE the pilot signal; stereophonic decoding means responsive to the derived composite modulation function and to the :regerlerated subcarrier signal. for developing a pair of output aud:Lo signal.s corresponding -to the first and second

3() stereophonically related audio signals; means responsive to the der:ived composite modulation function for producing the third component; and FM de-tector means responsive to the ~ls/J(~ - 6 -proclllced tll:ird comporlent Eor deve:lop:Lng a thircl au(1.1O outpllt s:igllal correspondinc3 to the third audio s:igna:L.
BRIEF DEscRlprrloM OF THE BRAW[NGS
FIG. 1 is a functional :block diagram of a television signal transmitter including apparatus for transmitting both the video and audio components of a -television signal.
FIG. 2 is a functional block diayram illustra-ting the preferred embodiment o:F a composite baseband signal source constructed according to the present invention useful for frequency modula-ting -the main audio R:F carrier signal produced by the carrier oscillator of FIG. 1.
FIG. 3 is a graphic representation of -the frequency spectrum of the composite baseband signal developed by the signal source of FIG. 2.
FIG. 4 is a functional block diagram of the por-tions of a television receiver adapted for reproducing the audio stereophonic components of the composite baseband signal illustrated in FIG. 3.
FIG. 5 is a functional block diagram illustrating a preferred embodimen-t of the 2fH subcarrier regenerator shown in FIG. ~, FIGS~ 6A and 6B are functional block diagrams illustra-ting -two alternate embodiments of the s-tero decoder of FIG. ~.
FIG, 7 is a functional block diagram of the portions oE a television receiver adapted for selectively reproducing ei.ther the stereophonic or the second language audio components o:E the cornposite baseband signal shown in F:~G. 3~
F'IG, 8 is a funct:ional bloclc diagram of a receiver 3() ada~ted for :reproducing the ENG component of the composite haseband s:Lgnal of FIG. 3.

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FIG. 9 is a ~ul-lctlorlal L)lock diagram o~ ~ receiver adapted for reE~rod-lcing the telernetry componellt of the composite baseballd signal of FIG. 3.

D~SCRI~T_)N Or TIIE: l~l~ ERRrD E~BODIMP.NT
Referriny now to the drawings and, in particular, to FIG. 1, a conventi~nal television signal -transmitter is shown to comprise a video channel 10 ancl an audio channel 20. The video channel 10 includes a source of video signals 12, a sync generator 14 connected to the video source 12 and an RF carrier oscillator 16, the oscillator 16 and the video source 12 supplying a video modulator 18. The video modula-tor 18 develops an output signal comprising a continuous sequence of horizontal scanning lines defined by the sync genera-tor 14, each horizontal scannirlg line consisting of the RF carrier developed at the output of the carrier oscillator 15 amplitude modulated by the output of the video source 12. According to FCC standards, the hori~on-tal scanning line frequellcy f~l is approximately 15.75 KHz. The output of the video modulator 18 is amplified by a power arnplifier 19 and coupled through a conventional diplexer 30 and transmitted via an antenna 32.
The aural channel 20 of the transmitter shown in FIG. 1 conventionally includes a source oE monaural audio signals 22 and an ~F carrier oscillator 24 both supplying an audio rnoclulator 26.
The output of the audio rnodulator 26, which consists of the RF
carrier developed at -the OlltpUt of the oscillator 24 frequency modulated by the output of the audio source 22, is arnplified by a power ampliEier 2B and coupled therefroln through the diplexer 30 for transrnission via the antenna 32. As discussed previously, the audio source 22 conventionally develops a monaural signal for transmission by the aural channel 20 of the television signal trans-mitter. ~s will be explained in detail hereinafter, it is a primary object of the yresent invention to more completely exercise the aural chanrlel 20 by irnpressing thereon a stereophonic audio signal together with a correspondin9 second language audio signal. In addition, ~ e inVentiOn furthel- discloses a technique by whicl~
dn ENG signal and a telemetry sicJnal may also be impressed on the audio channel 20.
F~I~. 2 illustrates a portion of the aural channel of a television signal -transmitter cons-tructed according to the present invention. The circuit illustrated in FIG. 2 which, in terms of the transmitter of FIG. 1, is represen-ted by the audio source 22, develops an output composite baseband signal having a spectrum as graphically represented in FIG. 3. Thifi cornposite baseband signal is used to frequency modulate the main aural carrier signal developed by the carrier oscillator circuit 24 and is coupled from the aural modulator 26 through the power amplifier 28 and the diplexer 30 for transmission by the antenna 32.
Referring now in detail to FIG. 2, the audio channel is seen to comprise a first audio source 34 and a second audio source 36 for developing a pair of stereophonically related audio signals L ~left) and R (right) respectively~ Audio sources 34 and 36 may comprise, for example, microphones, pickup circuits of a record player capable of reproducing a stereo recording or any other similar source of stereophonic audio signals. The outputs of the audio sources 34 and 36 are coupled -to a pair of 75 microsecond pre-emphasis networks 38 and 40 which, in a well known manner, emphasize the high frequency components of the audio signals relative to the low frequency cornponents thereof so as to achieve certain noise advantages. The outputs of the pre-emphasis network 38 and 40 are coupled through a pair of 15 KHz low pass filters 39 and 41,respectively,to the inputs of a pair of notch filter5 42 and 44. The notch filters 42 and 44 have frequency response characteristics centered at the horizontal scanning line frequency f~l Eor ren~oving any audio co~ponents from the signals L and R near the frequency fll and couple the filtered and emphasized audio signals to a stereo encoder 46.
The stereo encoder 46, as i.s well known in the art, may use either ti.me or frequency division multiplexing techniques for developing a main channel audio signal on a first output line 48 and a stereo subchanllel signal Oll a second output line 50. More specifically, the main cha~nel audio signal, which is limi-ted to a bandwiclth of 15 Kllz by -the low pass filters 39 and 41, comprises the arithmetic sum of the left and right stereophonic audio source signals (L + R) and is formed on the output line 48 by an addition process performed by the adder circuit 52. The stereo subchannel signal developed on output line 50 is fornled by using the difference between the leEt and right stereophonie source signals (L-R), this difference signal being developed at the output of a block repre-sented by a subtraetor circui-t 54, to arnplitude modulate a sub-carrier signal having a frequency 2fH in a balanced modulator 56 for producing a double sideband suppressed-carrier signal. The 2fH subcarrier signal is coupled to the modulator circuit 56 by a subcarrier and a pilot generator 58 which comprises a phase loclc circuit for phase locking the 2fH subcarrier signal to the second harmonic of the television signal horizontal sync pulses developed by the syne generator 14. The use of the 2fll subcarrier for the stereo subchannel signal avoids the production of audible beats with -the horizontal scanning line frequency while, at the same tirne, allowing for a 15 Kllz audio bandwidth. The subcarrier and pilot generator 58 also develops a pilot.signal on an output line 60 hav.ing a frequency f~l.
'l`he main channel audio signal developed on line 48, t:he stereo subchanrlel signal. developed on line 50 and the pilot signal developed on line 60 are all coupled oy a summation circuit 62 through a 47 Kllz linear phase low pass filter 64 to the first input 66 of a second sulr~ Lltion circuit 68 the output of sulrl~ tior circuit 6B corresponcling to the outE~ut of the audio source 22 of FIG. 1. That is the composite baseband signal developed at the output of sull~nation circuit ~8 is used to frequency Inodulate the main RY audio carrier in -the modulator 26. With reference to FIG. 3, the components of the composite baseband signal coupled to the inpu-t 66 of -the sumrnation circuit 68 -therefore include -the lS l<~z bandwidth (L+R~ main channe:L signal, the pilot signal at frequency EI~ and -the 15 Kl~z bandwidth upper and lower sidebands of the stereo subchannel siynal.
As mentioned above, the composite baseband signal developed at the output of summation circuit 68 is used to frequeney modulate the main RF aural carrier signal developed by oscillator 24. ~hile the maximum main aural carrier frequency deviation due to either the main channel signal or the stereo subchannel signal is limited to 25 KHz, in accordanee with the well known inter-leaving phenomenon charaeteristie of these signals, the total maximum main earrier frequeney deviation in response to hoth signals is limited to a to~al of 25 KHz. Ihe main earrier frequeney deviation due to the pilot signal is 2.5 Kllz so that the total main earrier frequency deviation due to the eomponents of the eomposite baseband signal coupled to the input 66 of summation eireuit 68 amounts to 27.5 Kllz.
The eireuit of FIG. 2 includes a third source of audio siynals 70 supplying, for example r a seeond language audio signal, it being intenc]ed that a viewer's television receiver is operable for seleetively reproducing either the stereophonie signal deseribed above or the seeond language audio signal. The seeond language source 70 :is eoupled through a pre--emphasis cireuit 72 and a 12 Kllz low pass filter 79 to one lnput of an FM modulator 76. The 12 Kllz audio bandwidth established by filter 74 is consiclered sufficient to al]ow better (~ucllity than i~, needed fc>r the pJ-ocess--iny of speech-type audio sicJnals alone, such compriC;irl(3 tile normal content of the audio signal develoE~ed by the source 70 thereby also ailowing Eor the processjng of some types of audio music signals. Altll0l1gh not shown in the drawings, this channel may incorporate compandiny techniques, e.g. of the Dolby or DBX
type, to further enhance the reproduction qualities of the second languaye signal.
The subcarrier and pilot yenerator 58 couples a subcarrier signal phase locked to 4fH to the second input of the FM modulato~
76. ~s a consequence, the EM modulator 76 develops an output signal COnSis-ting of -the 4fll subcarrier signal frequency modulated by the second language audio signal. It will be appreciated that cen-tering this signal at a harmonic of the horizontal scannillg line frequency fH effec-tively inhibits the generation of audible inter-modulation in the reproduced audio signal. The frequency modulated 4fH subcarrier signal is band pass filtered by filter 78 and coupled to the second input 80 of the summation circuit 68.
*he frequency characteristics of -the bandpass filter 78 and the extent of the frequency deviation of the main aural carrier due to the frequency modulated second language audio signal are selected so as to lirnit -the bandwidth of the frequency modulated second language audio siynal for preventing interference with adjacent channels. With reference to FIG. 3, the second language audio component of -the cornposite baseband signa] developed at the output o the sulnmatiorl circuit 68 is therefore seen to comprise a 4f~l subcarrier together with its associated upper and lower FM sidebands extendillg approximately 12 Ktlz above and below ~fll respectively.
The c:ircuit of FIG. 2 further :includes a source of ENG
(electrollic news gathering) signals 82 and a source of telemetry signals 84. 'rhe ENG signals, which a]low a broadca~ter to dirL~ctly com~ ic.lte wi~d~ tile st~t-ion's camer-a crews in ~l~e fielcl for real-t Lllle news re~)orts and ~he like, are coupled through a 150 microsecor,c] pre-ernphasis circuit 86 to t}-le illpUt of a 3.4 K~lz low pass fil-ter 88. Tlle resulting 3.4 Kll~ bandwidth siqnal is impressed as a fre(luellcy modulation on an approximately 5.5f subcarrier s,ignal by a second FM modulator 90 and coupled therefrom throug}l a bandpass filter 92 to a t:hird input 94 of the summation circuit 68. The t:eleme-try signals developed by the source ~4, which consist of transmissions from unattended trans~
mitter locations, are band limi-ted by a 2 Kl-l~ low pass filter 96 and subsequently impressed as frequency modulation on an approxi-mately 6.5f~l subcarrier si,gnal by a third FM modulator 98. 'I'he frequency modulated 6.5fH subcarrier signal is coupled from the modulator -through a bandpass filter 100 to a fourth and final input 102 of -the surnrnation cireuit 68. The FM modulated ENG and telemetry signals are effeetive for eausing maximum main aural carrier frequeney deviations of 4.0 and 1.25 KHz respeetively.
Typieal stereo demodulators are operative for demodula-ting a transmitted stereophonie signal a-t odd harmonies of the stereo subearrier freclueney. As diseussed above, the subearrier signal used to form the stereo subchannel signal in the eireuit of FIG. 2 is characteriæed by a frequency of 2fll, the third harmonie of whieh is equal to 6f1l. The use of a subearrier having a frequency of 6f~l for either the ENG signals or the telemetry signals would thererore eause in-terferenee with the stereo subehannel signal.
~eeordincJly, the subcarriers selected for use with these sic~nals have beell dispLaced abollt 0.5fl~ above and below the thircl harrnonie of the stereo subehannel subcarrier signal 2f~l.
It will thus be seen tha-t the particular four subcarriers seleeted for use in the eireuit: of FIG. 2 allow for the most effieient use of the audio barldwidth assoeiated with a transmitted television sign-ll. In partieular, referring to FIG. 3, it will 1 ~D ~

be observed that, considerirlg the 15 Kllz bandwidth of the rn~in ci~annel (L-~R) sic~nal and the 15 Kllz bandwidth of the lower side-bands of the stereo subchannel signal, the lowest harrnonic of the horizontal scanniny line frequency fH available for use as the stereo subchannel subcarrier is 2fll. As mentionecl previously, it is desirable to use a harmonic of the horizontal scanning line frequency fH for thls subcarrier in orcler to prevent the pro~uction of audible inter-modulation beats therebetween. Similarly, it is also desirable to use a harmonic of the hori~ontal scanning line frequency fH as the subcarrier for the second language audio signal.
Considering the 15 Kllz bandwid-th of the upper sidebands of the stereo subchannel siynal and the approximately 12 Kll~ bandwidth of -the second language signal, the next harmonic of the horizon-tal scanning line frequency f~ available for use as the second language subcarrier signal if 4fll. Allowing for sufficient separation be-tween the upper sidebands of -the frequency modulated second language signal and the lower sidebands of the frequency modulated ENG
signal, the next available harmonic of the horizontal scanning line frequency fH is 6fH. I-lowever, since 6f}i is an odd harmonic of the stereo subchannel subcarrier 2fH, its use as a subcar~rier is not desirable. Consequently, subcarriers for the ENG and telemetry signals are spaced about 0.5f~ therefrom at approximately 5 5fH
and 6.5fll. 'rhe rnain carrier deviations and associated fil-ter band-pass characteristics for these signals are so chosen to prevent in-terference with adjacent channels. Any resulting beating of the subcarriers Wit}l the hori~ontal scanning line frequency is expected to be minimal.
The Eorecloing subcarriers together with other pertinent data describirlg t;he operation of the circuit of FIG. 2 is presented in tabular form below-'I'~l3l r I

Modulating Si~]nal L~l~ Pilot L~ nd la~u~ ENG 'elernetry Subcarrier ~lodulation - CW AM E'M FM FM
DS~-SC

Subcarrier Frequency (~E~ f~ 2 f~l 4 fll5.5 fH 6~5fH

Subcarrier DeviatiOn (KHz) ~ ~ ~ 8 3.5 3.0 Max. Subcarrier Modulating Frequency (KHz~ 15 15 12 3.4 2.0 Pre-emphasi 5 (microseconds) 75 - 75 75 150 Main Carrier DeviatiOn (KHz) 25 2.5 25 15 ,4 1.25 To sumrnarize the foregoing, the composite baseband signal or composite modulation function produced a-t the output of the sumrnation circuit 68 and impressed as frequency modulation on the main aural RF carrier by modulator 26 comprises a series of distinct components. The ini-tial modulation function component comprises the 15 KHz main channel stereo signal (L~R) while the second component com-prises the double-sideband suppressed carrier amplitude modulated stereo subchannel signal. Together these two components account for a frequency deviation of the main aural carrier of 25 KHz. The third modulation function component comprises a pilot signal having a frequency of fll and accounts for an additional 2.5 KHz of frequency deviation of the Erequency modulated main aural carrier. The fourth rnodulation function component comprises the upper and lower sidebands together with the 4 f~l subcarrier of the frequency modulated second languaye audio siynal. This FM siynal provides another 15 ~lz of main carrier frequency deviation. The fifth and sixth modulation funct:ion colnponents comprise the upper and lower sidebancls and the 5~5 fl~ and 6.5 f~l subcarriers associated with the ENG and telemetry s:kJnals which account for a final contribu-tion of 4.0 and 1.25 K~lz respectively ~o the main carrier frequency deviation. The total main carrier frequency deviation due to the COlTlpOSi te baseband signal is therefore 47.75 KHz.
Whi.le the foregoinc~ discussion indicates that the 5.5fH and 6.5fH subcarriers are used for transmitting ENG and telemetry signals, -this should not be consiclered as a necessary limitation since these subcarrier signals may be used to -trans-mit various other types of information such as audio signals.
In the case where the 5.5f~ and 6.5fH subcarriers are used to transmit audio signals, the parameters of Table I are preferably modified as followso TABLE II

Subcarrier Frequency (KHz) 5.5fH 6.5fH
Subcarrier Deviation ~KHæ) 5.0 5.0 Max Subcarrier Modulating E~requency (KHz) 600 6.0 Pre-Emphasis (microseconds) 150 150 Main Carrier Deviation (KHz) 3.0 3.0 f~

FIG. 4 illustrates a televi.sion receiver constructed for reproducing the stereophoni.c sound -transmissions characteri~-ing the frequency modulated main aural RF carrier developed at the output of transmitting antenna 32. The receiver includes an antenna 110 for intercepting the transmit-ted RF signals, including both visual and aural components, which signals are coupled to a conventional television tuner 112. The tuner 112 converts the received RF signals to corresponding intermediate frequency (IF) signals which are amplified by an IF amplifier 114. The visual components of the amplified IF signal are coupled -to a video detector and therefrom to the remaining video processing circuits of -the television receiver while the inter-carrier components of the amplified IF signal are applied to a conventional FM detector stage 116. The FM detector stage 116 functions in a manner well known in -the art to demodulate the inter-carrier signal for recreati~g the composite baseband signal on output conductor 118. The com-posite baseband signal developed on conductor 118 is applied to one input of a conventional stereo decoder network 120 which receives a second input from a subcarrier regenerator network 122. The fH pilot signal developed Oll conductor 118 is coupled to an input of the regenerator network 122 which develops an output in response thereto comprising a regenerated 21~l subcarrier signal phase locked to the pilot signal. Alternatively, the regeneratox circuit 122 may operate in response to the horizontal sync signal developed in the llorLzontal d(rl-ec~::i()n st.~e or tl~e rcceiver, as indica~e(l by dotted line 129, Ior deve:loE)~r~cl t}~erefroln tlle 2il~ rec~enerclted sub-c~rrier siynal. In eithe~ case, the stereo decoder network 120 is responsive to the regenerated 2f~l subcarrier signal and to the main channel and stereo subchannel signals for developing emphasized representations of the Left ~L) and right (R) stereophonically re-lated audio signals on a pair of output conductors 126 and 128 respectively. These signals are de-emphasized by de-einphasis cir-cui-ts 130 and 132 -to form accurate reproductions of -the left (L) and right (R) stereophonically rela-t:ed audio signals wh:ich are coupled to separ-~-te speaker systems 134 and 136 -t}-lrough amplifiers 135 and 137 for conversion to corresponding audio sounds.
The 2fH subcarrier regenerator 122 of FIG. 4 may be of the conventional voltage controlled oscillator type but, preferably, comprises a phase-locked filter circuit of the type shown in FIG. 5. The advantage of this circuit is -that the loop bandwidth can be made extremely small for rejecting audio components of a signal frequency close to the pilot frequency. The bandwidth of a voltage controlled oscillator phase-locked loop cannot be made this small due to frequency pull-in considera-tions.
Referring to EIG. 5, the horizontal sync pulses developed on line 124 are converted to a corresponding sine wave signal by a pulse to sine wave converter circuit 141 and coupled therefrom -to the signal input of a voltage controlled phase shifter 143. The control input of the voltage controlled phase shif-ter 143 is derived from the output of a low-~ass filter 145 whose cut-off frequency determines the loop bandwidth. '~he output of the voltage controlled phase shiEter 143 is quadràture phase shifted by a phase shift circuit 147 and coupled to the first input of a phase detector 149, the second input of the phase detector 149 comprising the fll pilot signal developed on line 113. I'he pha5e 3'~

detec~or 149 develops an out~ut: error sigllal which is coupled t})rough t:he low-pass filter 145 to the control input of the voltage controlled phase shifter 143 for equalizing the phase of its output with the phase of the fH pilot signal. The output of the phase shiEter 143 accordingly comprises an extremely pure fH sinewave signal phase locked to the f~l pilot signal and therefore ideally suited for, after being douhled in frequency by a frequency doubler circuit 151, operating the stereo decoder 120~
FIGS. 6A and 6B generally illustrate two altern~te embodi-ments of the stereo decoder circuit shown in FIG. 4. The embodiment of FIG. 6A utiliæes time division multi,plexing techni ques and is preferred in the system of the invention while the embodiment of FIG. 6B utilizes fregu~ncy division multiplexing techniques. Referring specifically to FIG~ 6A, the fH pilot signal together with the horizontal sync pulses are coupled to the 2fH subcarrier regenerator 122, which preferably comprises the phase-locked loop filter circuit of FIG. 5, for synchronizing the operation thereof while the ~L-R) sideband signals are coupled to the inpu-t of a conventional switching demodulator 140. As is well known in the art, the switching demodulator 1~0 is oper-ative for effectively multiplying the (L-R) sideband signals by a 2fH square wave signal represented by the output of regenerator 122 to form an output signal which may be represented by the expression (L-R)+ 1l/4(L-~R). The latter slgnal together with the (L+R) rnain channel signal are appiied to the two inputs of a matrix 142 which suitably processes the signals for developiny the separate emphasized left (L) and right (R) audio signals on ~onductors 126 and 128 respectively. A particular advantage is achieved USinCJ the foregoing time division demultiplexing technique in ~hat the Fourier expansion of the square wave signal used to operate the switch:ing demodulator 190 includes odd order terms 1~ -only. ~s a conse~;uence, the 4f~l term is zero and none o:E the second lanyuage audio sign~l will -therefore appear in the output of the demodulator 140.
~ -IG. 6B illustrates the frequency division demultiplexing technique. In this case a ~oubly balanced demodulator 140' is used to develop an (L-R) signal which has no (L-~R) component.
The (L-R~ signal developed at the output of demodulator 140' is suitably combined with the (L~R) main channel. signal in a matrix 142' to develop the left (L) and right ~R) signals on 1~ conductors 126 and 128.
In conneCtiOn with the above, it is important to note that a conven-tional monaural television receiver tuned to a program broadcast stereophonically according to the above trans~
mission system will receive in its audio channel the (L~R) audio signal which will provide a perfec-tly satisfactory signal to listen to. On the other hand, a television receiver including a stereophonic sound reproduction system as shown in FIG. 4 and tuned to receive a monaural broadcast will produce the monaural sound in its (L+R) channel but will not produce the (L-R) audio signal due to the absence of the (L-R) sidebands. In this case, both speakers 134 and 136 will be fed the (L~R) audio signal for reproducing the monaural sound in a perfectly satisfactory manner.
FIG. 7 illustrates a modif.ication of the circuit of FIG. ~ whereby the viewer of a television receiver may select either the transmi.-tted stereophonic signals or, alternativeiy, the second language audio signal for reproduction. In this mod:ification, the stereo decoder 120, the 2fH subcarrier regenerator 122 and the de-emphasis ci.rcuits 130 and 132 are connected as sllown in FIG. ~. The line 118, however, downstream .3 o~ tl~e take-otr point for thc fll pilot signal incllldes a serially connerLL?d switch 1~4 (~an~Jed for operatiOn to~ether with a pair of switc}les 158 and 160 in response to a mllte control circuit 146. The circuit further includes a bandpass filter 148 passing the second language componellt of the composi-te baseband signal to an FM subcarrier detector 150. Tl)e output of the bandp~ss filter 148 i5 also coup:Led to a mute drive circuit 152 which detects the presence of an FM subcarrier signal. The output of the mute drive circuit 152 is connected to a mute control circuit 146 by a viewer operable selector switch 154. The output of the FM detector 150 is coupled by a de-emphasis circuit 156 to the inputs of switches 158 and 160 whose outputs are connected to the speakers 136 and 134 respectively. While the switches 144, 158 and 160 are schematically illustrated as mechanical in nature, it is preferred that these switches be implemented in an electronic for]n. Thus, for example, each of the switches 144, 158 and 160 may comprise a transis-tor switch operable in response to suitable output signals from the mute circui-t 146.
In operation, when the viewer selector switch 154 is in the position shown in FIG. 7, no drive signal can he supplied to the mute circuit 146 and the switches 144, 158 and 16~ assume the positions shown in the Figure. In this condition of the circuit the stereo decoder 120 is operative for energizing the speakers 134 and 136 through the de-emphasis circuit5 130 and 132 for produc-ing the separate stereophonic signals as described above. However, when the viewer selector switch 154 is moved to its closed position, the drive circuit 152, in response to the presence of a second languaye subcarrier signal, energizes mute circuit 146 which causes switch 14~ to open and switches 158 and 160 to close. The stereo decoder 120 is thereby decoupled from the FM detector 116 and, at the same time, signals are applied from the FM detector 116 through the bandpass filter 148 and the FM subcarrier detector 150 to the speakers 13~ and 1:36. Since the ~M subcarrier detector 15G

demod~ tes ~ he ~reqlllncy Illod~llated 4f~ second lan(Jucl~e subc.~rrier t~le speakers i3~ and 136 will rcproduce the second languac3e audio signal. If switch 154 is closed but no second language s~carrler is transmitted, the mute control is inoperative and the stereo signal is a~ltolnatically reproduced.
The fll pilot signal is also coupled from line 118 to the input of a pilot detector lS~. When the pilot detector 153 detects the presence of an input fl~ pilot ~igna:L it develops a si~naL on an output control line 155 conditioning the stereo decoder 120 for suitable demodulatirlg the stereo signals. In the absence of an fH
pilot signal, a control signal is developed on line 155 conditioning decoder 120 for operation in a monaural mode thereby preventing the possibility of decoding noise which rnight be present in the stereo subchannel.
FIG. 8 shows a circuit suitable for reproducing the trans-mitted ENG signals. It will be appreciated that only a receiver operated by the broadcasting station will include this circuit since the ENG signals are of no intereSt to the nonnal viewer.
The receiver includes a receiving antenna 162 for intercepting the transmitted main audio RF carrier and for coupling the received signal to the input of a tuner s-tage 164. The tuner 164 converts -the received RF audio carrier to a suitable IF
frequency which is amplified by an IF amplifier 166 and coupled to the input of an FM detector 168. The FM detector 168 recon-structs the composite baseband signal at its output and the ENG
component, i.e. the frequency modulated 5.5f~l subcarrier, is scparated therefrom by a bandpass filter 170. The ENG component of the composite baseband signal is then coupled to an FM subcarrier detector 172 which demodulates the 5.5fll frequency modulated sub-carrier. lhc demodulated subcarrier is subsequently coupled through a ]ow-pas6 filter 174 to rel-love any frequency components above 3.4K~I~ arid through a 150 microsecond de-emphasis circuit 176 where-lpon the ENG signal is reproduced by a speaker 178.
FIG. 9 illustrates a receiver suitable for reproducing the transl~ tcd telemetry signals. As in the case of the ENG

receiver of FIG~ ~, only a receiver used by the broadcasting station will include tl-is circuit. The receiver is substan-tially identical to the ENG receiver of FIG. 7 especially in its front end wIlere the antenIla 1~2, the tuner 164, the IF amplifier 166 and the l~M
detector 16~ are employed. Iiowever, a different bandpass filter 190 is used in this case to separate t:he 6.5f}I fraqueIlcy modulated telemetry subcarrier from the composit.e baseband signal developed at the output of the FM detector 168. The frequency modulated telemetry subcarrier signal is subsequently demodulated by an FM subcarrier detector 192 and coupled -through a low-pass filter 194 for removing any Erequency components above 2.0 KIIz.
'rhe filtered telemetry signal may then be coupled to a suitable digital processing and readout circuit 198.
What has -thus been shown is a television audio trans-mission system, including transmitting and receiving appara-tus, which system comprehensively exercises the available audio band-width with minimum deleterious effects. In particular, the selection and use of the specific subcarrier signals to produca the composite baseband signal frequency modulating the main audio RF carrier is considered to produce advantageous resu;ts hereto-fore unattained.
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the ar-t that changes and modifications may be macIe without departing from the invention in its broader aspec-ts, and therefor, the aim in the appended claims is to cover all such changes and modifica-tions as fall within -the true spirit and scope of the invention.

- 2~ -g~

SUI~PLIMEN~I~Ai~Y l)[S(''IOSURE

BRIEF DESCRLPTION OF ~ IE l)RAWINGS
__ __ __ _ PIG. 10 is a graph-ic representation of the frequency spectrum of an alternate composite basebanci signal accordinq to the invention.
E'IG. 11 is a Eunctional block cliagram i,llllstrating a composite baseband signal source adapted for producing the composite baseband siqnal shown in FIG. 10.

DESCRIPTION OF TE3E ALq'ERN~q'E EMBODIMENT
FIG. 10 :Lllustrates the frequency spectrurn of an alternate embodiment of the present invention. It has been found that the -transrnission standard defined by the graph of FIG. 3 adversely affects the audio reproducing character-istics of certain monaural television receivers currently in the field. In particular, it has been found that an objectionable amount oE cross-talk may exist between the 4fH subcarrier and -the monaural audio channel of these -te],evis:ion receivers. This cross-talk may be largel,y avoided by modifying the transrnission standard of E~:rG~ 3 as illustrated in FIG. 10.
Referring to FIG. 10, it will be seen that the frequency spectrum illustrated therein is sLmilar to that shown in FIG. 3 except that the subcarrier Eor the second language signal has been displaced from ~EH to 5FW and that the channel defi,ned by the 5 5fEl Erequency modulated subcarrier has been el:i,minated. This displacement of the seconcl languacle subcarrier signal to 5EEI has been found to largely el,:iminat:e the previously described cross-talk problem without at al], impacting the stereo transmission scheme oE FIG. 3.
E'[G. 11 illustrates a composite baseband signa'L
source similar to that of E'IG. 2 but conEigured for mg/~ - 23 -proclucirl~ tlle bilseballcl sigllal deEined by the frequellcy spectrum oE FIG. lO. Since the circuit of FrG. 11 is conEigured and operates :in a manner nearly identical to the circuit of FIG. 2, for purposes oF brevity, a detai:led discussion thereof will not be repeated at this point.
Suffice it to say that -the two circuits are identical except -that, in the case of the circuit of E~IG. 11, the subcarrier and pilot qenerator 5i3 couples a subcarrier signal phase lockecl to 5EH rather than 4fH to the second input of the FM modulator 76 in the second languacJe channel.
In addition, the channel defined by the 5.5fE~ subcarrier has been eliminated and the channel defined by the 6.5fH
subcarrier has been relabled as an auxiliary channel which may be used to transmit either audio or dig:Ltal type information. When used to transmit digital inEormation, the 6.5fH channel preferably includes the 2KHz low pass filter 96, the remaining transmission parame-ters being as shown ln Table 1 for the ~i~elemetrychannel except that the main carrier deviation may be increased to 3.0 KHz. When used to transmit audio signals, filter 96 is preferably removed and replaced by a voice bandwidth filter from the cilannel, the remainincJ transmission parameters being as shown in Table 1 for the ENG channel except that the sub-carrier and the main carrier deviations may both be reduced to 3.0 KHz.
The television receiver circuLts illustrated in l;'IGS. 4-7 may be used to process the s:Lgnal produced by -the trarlsm:itter of E`LG. 1 incllldirly the audio source shown in F[G. :Ll, the only diEference being that the bandpass filter 1~8 of E'IG. 7 must be conEigured Eor coupling the 5fH
second 1anguacJe sicJnal to F'M subcarrier cletec-tor lSO For processirl~ instead of the 4F~ subcarrier. The receiver of mg/c~j - 24 -c3 FIG. 9 may be uge(l to process cl:i.gital siclnals transm:itted over the 6.51~ charlrlel oE I;'rG. ll while a sirnilar receiver including an auclio output: circuit may be used to process audio signal.s transmitted over the channel.
~ hile a particu]ar embocliment of the invent:ion has been shown and descri.bed, it will be obvious to those skilled in the art that cllanges and mod:ifications may be made Wit}lOUt departing Erom the i.nvention in its broader aspects, and therefor, the aim in the appended claims is to cover all such changes and modificati.ons as fall within the true spirit and scope of -the invention.

mg/ 'l~ - 24a -

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency 4fH frequency modulated in accordance with a third audio signal, and a fourth component comprising a pilot signal having a frequency fH, where fH
is the horizontal scanning line frequency associated with the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for deriving said composite modulation function;
means responsive to said derived composite modulation function for regenerating said first subcarrier signal in a form phase and frequency locked to the second harmonic of said pilot signal;
stereophonic decoding means responsive to said derived composite modulation function and to said regenerated subcarrier signal for developing a pair of output audio signals corresponding to said first and second stereophonically related audio signals;
means responsive to said derived composite modulation function for producing said third component; and FM detector means responsive to said produced third component for developing a third audio output signal corresponding to said third audio signal.

2. The receiver according to claim 1 wherein said means for producing said third component comprises a bandpass filter having a center frequency equal to approximately 4fH.

3. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, and a third component comprising a pilot signal having a frequency fH, where fH is the horizontal scanning line frequency associated with the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for deriving said composite modulation function;
phase-locked filter means responsive to said horizontal sync signal and to said pilot signal for regenerating said first subcarrier signal in a form phase and frequency locked to the second harmonic of said pilot signal; and stereophonic decoding means responsive to said derived composite modulation function and to said regenerated subcarrier signal for developing a pair of output audio signals corresponding to said first and second stereophonically related audio signals.

4. The receiver according to claim 3 wherein said phase locked filter comprises a voltage controlled phase shifter responsive to said horizontal sync pulses, phase detector means responsive to said pilot signal and to the output of said voltage controlled phase shifter for applying an error signal to said phase shifter locking the phase of the output thereof to the phase of said pilot signal and means for doubling the frequency of the output of said phase shifter for producing said regenerated first subcarrier signal.

5. The receiver according to claim 4 including a relatively narrow bandwidth low-pass filter for coupling said error signal from said phase detector means to said phase shifter means.

6. The receiver according to claim 5 wherein said stereophonic decoding means comprises time division demultiplexing means for developing said pair of output signals.

7. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals and a third component comprising a second subcarrier having a frequency 4fH frequency modulated in accordance with a third audio signal, where fH is the horizontal scanning line frequency associated with the horizontal sync signal of a transmitted television signal, said receiver comprising:

input means responsive to a transmitted television signal for developing a first signal corresponding to said composite modulation function;
a bandpass filter having a center frequency of 4fH
and responsive to said first signal for developing a sound signal corresponding to said third component of said composite modulation function;
means for regenerating said first subcarrier signal;
stereophonic decoding means responsive to said first signal and to said regenerated subcarrier for developing a pair of output audio signals corresponding to said first and second stereophonically related audio signals; and an FM detector responsive to said second signal for developing a third audio output signal corresponding to said third audio signal.

8. The receiver according to claim 7 wherein said composite modulation function includes a fourth component comprising a pilot signal having a frequency fH, said means for regenerating being responsive to said pilot signal and to said horizontal sync signal for phase and frequency locking said regenerated first subcarrier signal to the second harmonic of said pilot signal.

9. The receiver according to claim 8 including first and second speaker means and switching means selectively operable for coupling said first and second stereophonically related audio signals, respectively, to said first and second speaker means or for coupling said third audio signal to said first and second speaker means.

10. The receiver according to claim 5 including first and second de-emphasis means for de-emphasizing said first and second stereophonically related audio signals respectively, each of said first and second de-emphasis means having a time constant of 75 microseconds.

11. The receiver according to claim 10 wherein said input means comprises tuner means for converting said transmitted television signal to an intermediate frequency signal including an intermediate frequency sound signal, filter means for separating said intermediate frequency sound signal from said intermediate frequency signal and FM
detector means for deriving said composite modulation function from said intermediate frequency sound signal.

12. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency 4fH frequency modulated in accordance with a third audio signal, a fourth component comprising a third subcarrier having a frequency approximately 5.5fH frequency modulated in accordance with a first information signal and a fifth component comprising a fourth subcarrier having a frequency approximately 6.5fH frequency modulated in accordance with a second information signal, where fH is the horizontal scanning line frequency defined by the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for developing a baseband signal corresponding to said composite modulation function; and decoding means responsive to said baseband signal for developing therefrom said first and second stereophically related audio signals, said third audio signal, said first information signal and said second information signal.

13. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency 4fH frequency modulated in accordance with a third audio signal, a fourth component comprising a third subcarrier having a frequency approximately 5.5fH frequency modulated in accordance with a first information signal, a fifth component comprising a fourth subcarrier having a frequency approximately 6.5fH frequency modulated in accordance with a second information signal and a sixth component comprising a pilot signal having a frequency fH, where fH is the horizontal scanning line frequency defined by the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for developing a baseband signal corresponding to said composite modulation function;
phase locked filter means responsive to said pilot signal and to said horizontal sync signal for regenerating said first subcarrier signal in a form phase and frequency locked to the second harmonic of said pilot signal; and decoding means responsive to said baseband signal and to said regenerated subcarrier signal for developing therefrom said first and second stereophonically related audio signals, said third audio signal, said first information signal and said second information signal.
14. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency equal to an integral multiple greater than three times fH frequency modulated in accordance with a third audio signal, and a fourth component comprising a pilot signal having a frequency fH, where fH is the horizontal scanning line frequency associated with the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for deriving said composite modulation function;
means responsive to said derived composite modulation function for regenerating said first subcarrier signal in a form phase and frequency locked to the second harmonic of said pilot signal;
stereophonically decoding means responsive to said derived composite modulation function and to said regenerated subcarrier signal for developing a pair of output audio signals corresponding to said first and second stereophonically related audio signals;

Claim 14....continued.

means responsive to said derived composite modulation function for producing said third component;
and FM detector means responsive to said produced third component for developing a third audio output signal corresponding to said third audio signal.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

15. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, A second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency 5fH frequency modulated in accordance with a third audio signal, and a fourth component comprising a pilot signal having a frequency fH, where fH is the horizontal scanning line frequency associated with the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for deriving said composite modulation function;
means responsive to said derived composite modulation function for regenerating said first subcarrier signal in a form phase and frequency locked to the second harmonic of said pilot signal;
stereophonic decoding means responsive to said derived composite modulation function and to said regenerated subcarrier signal for developing a pair of output audio signals corresponding to said first and second stereophonically related audio signals;
means responsive to said derived composite modulation function for producing said third component; and FM detector means responsive to said produced third component for developing a third audio output signal corresponding to said third audio signal.

16. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals and a third component comprising a second subcarrier having a frequency 5fH frequency modulated in accordance with a third audio signal, where fH is the horizontal scanning line frequency associated with the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for developing a first signal corresponding to said composite modulation function;
a bandpass filter having a center frequency of 5fH
and responsive to said first signal for developing a sound signal corresponding to said third component of said composite modulation function;
means for regenerating said first subcarrier signal;
stereophonic decoding means responsive to said first signal and to said regenerated subcarrier for developing a pair of output audio signals corresponding to said first and second stereophonically related audio signals; and an FM detector responsive to said second signal for developing a third audio output signal corresponding to said third audio signal.

17. The receiver according to claim 16 wherein said composite modulation function includes a fourth component comprising a pilot signal having a frequency fH, said means for regenerating being responsive to said pilot signal and to said horizontal sync signal for phase and frequency locking said regenerated first subcarrier signal to the second harmonic of said pilot signal.

18. The receiver according to claim 17 including first and second speaker means and switching means selectively operable for coupling said first and second stereophonically related audio signals, respectively, to said first and second speaker means or for coupling said third audio signal to said first and second speaker means.

19. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency 5fH frequency modulated in accordance with a third audio signal and a fourth component comprising a third subcarrier having a frequency approximately 6.5fH frequency modulated in accordance with a first information signal where fH is the horizontal scanning line frequency defined by the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for developing a baseband signal corresponding to said composite modulation function; and decoding means responsive to said baseband signal for developing therefrom said first and second stereophonically related audio signals, said third audio signal and said first information signal.

20. A receiver for a television signal transmission system characterized by a transmitted aural signal comprising a main carrier signal frequency modulated in accordance with a composite modulation function having a first component comprising the sum of first and second stereophonically related audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a first subcarrier having a frequency 2fH in accordance with the difference between said stereophonically related audio signals, a third component comprising a second subcarrier having a frequency 5fH frequency modulated in accordance with a third audio signal and a fourth component comprising a third subcarrier having a frequency approximately 6.5fH frequency modulated in accordance with a first information signal, and a fifth component comprising a pilot signal having a frequency fH, where fH is the horizontal scanning line frequency defined by the horizontal sync signal of a transmitted television signal, said receiver comprising:
input means responsive to a transmitted television signal for developing a baseband signal corresponding to said composite modulation function;
phase locked filter means responsive to said pilot signal and to said horizontal sync signal for regenerating said first subcarrier signal in a form phase and frequency locked to the second harmonic of said pilot signal; and decoding means responsive to said baseband signal and to said regenerated subcarrier signal for developing therefrom said first and second stereophonically related audio signals, said third audio signal and said first information signal.