[54]
`
`[75]
`
`[73]
`
`United States Patent pn
`Dougherty
`
`APPARATUS AND METHOD FOR
`INJECTING AN ANCILLARY SIGNAL INTO
`A LOW ENERGYDENSITY PORTION OF A
`COLOR TELEVISION FREQUENCY
`SPECTRUM
`
`US005629739A
`[11] Patent Number:
`[45]
`Date of Patent:
`
`5,629,739
`May 13, 1997
`
`3,842,196 10/1974 Loughlin, esnsmensetensetnsesen 358/12
`. 348/486
`3,924,060 12/1975 Bedford ............
`
`....cssecsssecsenes 325/31
`4,025,851
`5/1977 Haselwood et al.
`
`4647974
`3/1987 Buder et al...
`348/473
`4/1995 Douglas et al. cecsnnnnsuuunsnn 348/1
`5404161
`
`FOREIGN PATENT DOCUMENTS
`
`Inventor: Robert A. Dougherty, Ozona, Fla.
`
`WO94/10799
`
`5/1994. WIPO seesetssnnnemnnse HOAN 7/00
`
`Assignee: A.C. Nielsen Company, Schaumburg,
`ill.
`
`[21] Appl. No.: 399,187
`[22] Filed:
`Mar. 6, 1995
`[51]
`Int. Co ciecccessseccsesnsessscssssesescncscesesanssessuesses HOAN 7/081
`[52] US. CH. crcsccscseccssssenscovesensnes 348/486; 348/1; 348/473
`[58] Field of Search 0...cesses 348/1, 473, 486,
`348/4; HO4N 7/081
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
` S/1961 Hathaway ..rsseserccsssscosecceesssee 178/5.6
`9/1974 Loughlin et al. oeeeeeeeeee 178/5.2
`
`2,982,813
`3,838,444
`
`Primary Examiner—Victor R. Kostak
`Attorney, Agent, or Firm—Marshall, O’Toole, Gerstein,
`Murray & Borun
`ABSTRACT
`57]
`An ancillary signal is injected into a program signal within
`the frequency band normally occupied. by the program signal
`alone. The program signal includes a modulated carrier
`having a carrier frequency and a low energy density portion
`of the frequency band. The ancillary signal is selectively
`added at an injection frequency within the lower energy
`density portion of the frequency band so thatthe injection
`frequency is locked to the carrier frequency and to the
`frequency of a local oscillator.
`
`52 Claims, 1 Drawing Sheet
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`5,629,739
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`U.S. Patent
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`May13, 1997
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`NOILDSPNI
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`OULNOD
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`5,629,739
`
`1
`APPARATUS AND METHOD FOR
`INJECTING AN ANCILLARYSIGNAL INTO
`A LOW ENERGYDENSITY PORTION OF A
`COLOR TELEVISION FREQUENCY
`SPECTRUM
`
`TECHNICAL FIELD OF THE INVENTION
`
`The present invention relates to a system and a methodfor
`compatibly transmitting and receiving both a program signal
`and an ancillary signal within the frequency band normally
`occupied by the program signal alone and, moreparticularly,
`to a system and method for compatibly transmitting and
`receiving both a color television program signal and an
`ancillary signal so that the ancillary signal is added to a low
`energy density portion of the color television program
`signal.
`
`BACKGROUND OF THE INVENTION
`
`It is known to add ancillary signals to radio frequency
`signals in order either to monitor the broadcasts of programs
`or to measure audiences of programs. Such programs may
`include television programs, radio programs, and/orthe like,
`and the broadcast of such programs may include the trans-
`mission of these programs over the air, over a cable, via a
`satellite, and/or the like.
`When monitoring the broadcast of programs, a monitor-
`ing system typically determines the identity of the programs
`which were broadcast, the regions in which these programs
`were broadcast, the times at which these programs were
`broadcast, and the channels over which these programs were
`broadcast. One monitoring system, which is commonly used
`within the United States, is referred to as the “AMOL”
`system and is taught by Haselwood, etal. in U.S. Pat. No.
`4,025,851. This “AMOL”system adds a source identifica-
`tion codeto selected horizontal lines onthe vertical blanking
`intervals of the program signal. Monitoring equipment,
`which is located in selected regions throughout the United
`States, determines the identity of the programs which are
`broadcast by detecting the sourceidentification codes of the
`broadcast programs. The monitoring equipment stores, for
`later retrieval, these detected source identification codes
`together with the times at which these source identification
`codes were detected and the channels on which these source
`identification codes were detected.
`When measuring the audiences of programs, an audience
`measurement system typically determines which programs
`were viewed by which membersofa statistically sampled
`panel of dwellings. One type of an audience measurement
`system uses an ancillary signal
`to monitor a program
`receiver, and commonly injects this ancillary signal (which
`may be a simple tone, or a complex digital code) into a
`channel that may be carrying a viewed program. The ancil-
`lary signal is injected by an apparatus which is located at or
`near the program receiver being monitored. The detection of
`such an ancillary signal provides an indication that the
`program receiver is on and is tuned to the channel carrying
`the detected ancillary signal. Signal injection systems are
`taught, inter alia, in PCT/US93/09458 by Mostafa, etal.
`Adding an ancillary signal
`to a program signal must
`generally be done so as to minimize the probability that the
`ancillary signal will interfere with any aspect of the basic
`program signal. Several systems are known which add
`ancillary signals at selected frequencies within the radio
`frequency band, or channel, of a program signal. For
`example, in U.S. Pat. No. 2,982,813, Hathaway teaches a
`system which frequency interleaves the ancillary and pro-
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`gram signals. In U.S. Pat. No. 3,838,444, Loughlin,et al.
`teach a system which compatibly adds and transmits an
`ancillary signal in a low energy density portion of a color
`television frequency spectrum. The low energy density
`portion of interest is located between the video carrier and
`the color subcarrier of the NTSCtelevision signal, and is at
`a frequency which is about 2.4 MHz abovethe video carrier
`peak in the radio frequency band of the NTSC television
`signal. The teachings of Loughlin, et al. in U.S. Pat. No.
`3,838,444 are herein incorporated by reference.
`Furthermore, in U.S. Pat. No. 3,842,196, Loughlin dis-
`closes an improved system which minimizes interference
`between a primary ancillary signal and the program signal
`by adding a redundant ancillary signal. The redundant
`ancillary signal is transmitted with an inverted polarity as
`compared to the primary ancillary signal so that artifacts
`which may be caused by the addition of an ancillary signal
`to the program signal are canceled in the video display.
`However, the accuracy with which these systems set the
`absolute frequency of the ancillary signal which is to be
`injected into the program signal is limited. For example, a
`reasonable error (e.g., +50 KHz) in setting the frequency
`(e.g., 100 MHz)ofthe ancillary signal can causethe injected
`ancillary signal to overlap a harmonic of the horizontal
`scanning frequency. If the frequency of the ancillary signal,
`because of an error, overlaps a harmonic of the horizontal
`scanning frequency, the ancillary signal will interfere with
`the program signal. This interference is annoyingly apparent
`to a viewer. Moreover, if the frequency of the ancillary
`signal is uncertain, a monitoring system or an audience
`measurement system may havedifficulty in picking up and
`using the ancillary signal for program monitoring and/or
`audience measurement purposes.
`The present invention overcomes one or more of these
`problems
`
`SUMMARY OF THE INVENTION
`
`Therefore, according to one aspect of the present
`invention, a method for compatibly transmitting and receiv-
`ing both a program signal and an ancillary signal within a
`frequency band normally occupied by the program signal
`alone, wherein the program signal includes a modulated
`carrier having a carrier frequency and a low energy density
`portion of the frequency band, comprises the steps of (i)
`receiving the program signal, and(ii) selectively addingthe
`ancillary signal at an injection frequency within the lower
`energy density portion of the frequency band so that the
`injection frequency is locked to the carrier frequency.
`According to another aspect of the present invention, a
`system compatibly transmits and receives both a program
`signal and an ancillary signal within a frequency band
`normally occupied by the program signal alone. The pro-
`gram signal includes a modulated carrier having a carrier
`frequency and a low energy density portion of the frequency
`band. The system comprises a receiver and a signal injector.
`The receiver is arranged to receive the program signal, and
`the receiver has a local oscillator which produces a local
`oscillator frequency. The signal injector is arranged to
`selectively add the ancillary signal at an injection frequency
`within the lower energy density portion of the frequency
`band so that the injection frequency is locked to the local
`oscillator frequency.
`Accordingto still another aspect of the present invention,
`a system compatibly transmits and receives a television
`program signal and an RF ancillary signal. The television
`program signal is in a predetermined RF frequency band,
`
`

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`5,629,739
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`3
`and the television program signal has a modulated video
`carrier signal and a low energy density portion of the
`frequency band. The system comprises a tuner, first and
`second mixers, and a coupler. The tuner is arranged to
`receive the television program signal and has as outputs a
`local oscillator signal and a modulated carrier signal. The
`first mixer is arranged to mix an injection signal at a
`predetermined baseband injection frequency with a signal
`representative of the modulated carrier signal to produce an
`intermediate frequency injection signal. The second mixeris
`arranged to mix the local oscillator signal with the interme-
`diate frequency injection signal to produce the RF ancillary
`signal. The coupler is arranged to couple the RF ancillary
`signal into the received television program signal.
`According to yet another aspect of the present invention,
`a method of injecting an RF ancillary signal into a low
`energy density portion of a channel normally occupied by a
`colortelevision program signal, wherein the colortelevision
`program signal has a modulated video carrier, a chromi-
`nance subcarrier, and the low energy density portion, com-
`prises the steps of (i) tuning the color television program
`signal so as to produce a local oscillator signal and a
`modulatedcarrier signal as outputs, (ii) mixing an injection
`signal at a predetermined injection frequency with a signal
`representative of the modulated carrier signal to produce an
`outputinjection signal, (iii) mixing the local oscillator signal
`with the output injection signal to produce the RF ancillary
`signal, and (iv) coupling the RF ancillary signal into the
`color television program signal.
`According to a further aspect of the present invention, a
`broadcast tuning measurement method in which an RF
`ancillary channel recognition signal is added to a television
`program signal received at a predetermined channel fre-
`quency within a sampled dwelling unit, wherein the RF
`ancillary channel recognition signal is subsequently read
`from the television program signal at a viewing site, com-
`ptises the steps of(i) tuning the television program signal so
`as to produce a local oscillator frequency and a video carrier
`signal as outputs, (ii) providing an injection signal at a
`predetermined frequency which is selected to be in a low
`energy density part of a channel, (iii) combining the video
`carrier signal with the injection signal to form a carrier/
`injector signal, (iv) combining the local oscillator frequency
`with the carrier/injection signal to form the RF ancillary
`channel recognition signal, and (v) coupling the RF ancillary
`channelrecognition signal into the television program sig-
`nal.
`
`DESCRIPTION OF THE DRAWING
`
`These and other features and advantages will become
`apparent from a detailed consideration of the present inven-
`tion when taken in conjunction with the single FIGURE of
`the drawing which is a schematic block diagram of a signal
`injection apparatus of the present invention.
`
`DETAILED DESCRIPTION
`
`A receiving and encoding apparatus 10 is located within
`a selected dwelling 12 at or near a signal entrance 14 at
`which television signals from a signal source 16 enter the
`selected dwelling 12. The receiving and encoding apparatus
`10 encodesall television signals on all channels receivable
`from the signal source 16. In the specific embodimentof the
`present invention shown in FIG. 1, the source of program
`signals, i.e. the signal source 16, is shown as an antenna.
`However, the signal source 16 may alternatively be a sat-
`ellite dish, a cable, and/or the like. Moreover, although only
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`one source of program signals, i.e., the signal source 16, is
`shown, additional sources may supply program signals to
`the selected dwelling 12. If so, either a single receiving and
`encoding apparatus 10 may encodeall television signals on
`all channels from all sourcesor, preferably, a receiving and
`encoding apparatus 10, which encodesall television signa-
`tures on all channels of a corresponding source, may be
`provided for each source. Other variations are, of course,
`possible.
`If sources of program signals are provided for the selected
`dwelling 12 in addition to the signal source 16, and if each
`such source has its own corresponding receiving and encod-
`ing apparatus 10, each such receiving and encoding appa-
`ratus 10 should preferably be located or near the service
`entrance through which its corresponding program signal
`source enters the selected dwelling 12. Because each receiv-
`ing and encoding apparatus 10 is located at or near the
`service entrance through which the television signals receiv-
`able from a corresponding source of program signals enter
`the selected dwelling 12, each receiving and encoding
`apparatus 10 may be easily arranged to encode only the
`television signals on the channels receivable from its cor-
`responding source of program signals. Accordingly, if all
`such sources of program signals are encoded at their respec-
`tive signal entrances, the source of programs to which a
`teceiver within the selected dwelling 12 is tuned may be
`morereadily identified.
`The selected dwelling 12 may contain a first viewingsite
`18. Additionally, the selected dwelling 12 may contain a
`second viewing site 20. More or fewer viewing sites may be
`contained within the selected dwelling 12 as is desirable. It
`will be understood that, although the embodiment of the
`invention shown in the drawing includes various known
`elements of the television audience measurement art, the
`method and apparatus of the present invention are more
`broadly directed to any system in which the addition of an
`ancillary signal to a program signal is advantageous.
`The receiving and encoding apparatus 10 is connected to
`the signal source 16 oftelevision program signals by way of
`a splitter 22, for example. A tuner 24 is connected to an
`output of the splitter 22. The tuner 24 periodically and
`sequentially tunes to each of the television channel frequen-
`cies available from the signal source 16. The tuner 24
`includes a local oscillator 26 and has an output 28. As is well
`knownin the tuner art, the tuner 24 mixesthe frequency of
`the signal provided by the local oscillator 26 with the
`television channel frequencies, which are available from the
`signal source 16 and which are selected by the tuner 24,in
`order to down convert the selected television channel fre-
`quencyto an intermediate frequency. The signal havingthis
`intermediate frequency is provided by the tuner 24 on the
`output 28.
`In the receiving and encoding apparatus 10, the signal on
`the output 28 of the tuner 24 is applied to a video carrier
`bandpassfilter 30 which is centered on the intermediate
`frequency of the video carrier (e.g., which is 45.75 MHzin
`a conventional NTSC receiver). The video carrier bandpass
`filter 30 is selected to pass the intermediate frequencyof the
`video carrier, to reject the other intermediate frequencies,
`and to have a passband which is wide enough to accept the
`worst case off-frequencyerror in the intermediate frequency
`of the video carrier which is expected to be encountered
`(e.g., a 100 KHz luminance frequency error on a locally-
`originated cable channel). The video carrier bandpassfilter
`30 provides the intermediate frequency video carrier to a
`video carrier reconstruction circuit 32.
`The video carrier reconstruction circuit 32 includes a
`phase detector 34 and a voltage controlled oscillator 36. The
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`video carrier reconstruction circuit 32 phase locks the volt-
`signal of the code-adding balanced mixer 38 is about
`43.350525 MHz.
`age controlled oscillator 36 to the video carrier reference
`signal from the video carrier bandpass filter 30 in order to
`The sideband stripping filter 48 is preferably a bandpass
`generate an unmodulated, reconstructed videocarrier signal
`filter centered on the frequency F,, of the second interme-
`which has a frequency F,,, and which is applied toafirst
`diate frequency encodedancillary output signal of the code-
`input of a code-adding balanced mixer 38. Thus, the video
`adding balanced mixer 38. The frequency F,, of the second
`carrier reconstruction circuit 32 selects from the output of
`intermediate frequency encoded ancillary output signal is
`the lower sideband frequency of the intermediate frequency
`the video carrier bandpassfilter 30 only the frequency of the
`encoded ancillary output signals produced by the code-
`intermediate frequency video carrier and excludes all other
`adding balanced mixer 38. Moreover, the sidebandstripping
`frequencies which may pass through the video carrier band-
`filter 48 preferably has a passband width sufficient to pass a
`pass filter 30. Also, because the unmodulated, reconstructed
`worst case off-frequency error which, for example, may be
`video carrier signal having the frequency F,,-is derived from
`+100 KHz. The sideband stripping filter 48 necessarily has
`the frequency of the local oscillator 26 and from the fre-
`a narrow enough passband to reject the first intermediate
`quency of the modulated video carrier of the television
`frequency encoded ancillary output signal of the code-
`channel selected by the tuner 24, any shift in the frequency
`adding balanced mixer 38. The frequencyof the first inter-
`of the local oscillator 26 or in the video carrier frequency
`mediate frequency encoded ancillary output signal is the
`selected by the tuner 24 leads to a corresponding shift in the
`- higher sideband frequency of the intermediate frequency
`frequency of the unmodulated, reconstructed video carrier
`encoded ancillary output signals produced by the code-
`signal having the frequency F,, provided by the video
`adding balanced mixer 38.
`carrier reconstruction circuit 32 to the code-adding balanced.
`mixer 38. Thus, as will be subsequently discussed in greater
`The second intermediate frequency encoded ancillary
`detail, the apparatus of the present invention locks the
`output signal of the code-adding balanced mixer 38, which
`frequency at which theancillary signal is injected to both the
`is filtered by the sideband stripping filter 48 and which has
`received video carrier frequency of the television channel
`the frequency F_.,, is applied to a first input of a balanced up
`currently selected by the tuner 24 andto the frequency of the
`converting mixer 50. The signal provided by the local
`signal provided by the local oscillator 26 in order to ensure
`oscillator 26, which has a frequency F,, is available as an
`that the ancillary signal is indeed injected into the desired
`output from the tuner 24 and is applied to a second input of
`lower energy density portion of the selected television
`the balanced up converting mixer 50. The balanced up
`channel.
`:
`converting mixer. 50 mixes the second intermediate fre-
`quency encoded ancillary output signal, which is filtered by
`An injection signal circuit 40 supplies an injection signal,
`the sideband strippingfilter 48 and which has the frequency
`which has a frequency F,,, to a second input of the code-
`F,5, and the output signal of the local oscillator 26, which
`adding balanced mixer 38. The injection signal circuit 40
`has the frequency F,. Accordingly, the balanced up con-
`includes an oscillator 42 and an encoder 44. The frequency
`verting mixer 50 produces first and second intermediate
`of the oscillator 42 may be, for example, 2.399475 MHz,
`which is the 305th harmonic of one-half of the horizontal
`frequency tracking signals having corresponding sum and
`difference frequencies F,+F, and F,5-F,9.
`scan rate in an NTSCtelevision signal, and the encoder 44
`may be any known encoder capable of modulating the
`Continuing the NTSC example discussed above, if the
`oscillator 42. (It should be noted here that, when the fre-
`tuner 24 is tuned to VHF channel3 (i.e., 61.25 MHz) sothat
`quency of about 2.399475 MHzis addedto the frequency of
`the local oscillator 26 produces a frequency F,, of 107
`MHz, the first and second intermediate frequency tracking
`a video carrier, the resulting frequency is within the low
`energy density portion of the color television program
`signals have corresponding sum and difference frequencies
`signal.) A time-stamped code may be added to the output of
`F,s+F_o and F,,-F, of about 150.350525 MHz and about
`the oscillator 42 and, if so, may be derived from a clock 46.
`63.649475 MHz. The second intermediate frequency track-
`Alternatively, a title code, a channel number code, a source
`ing signal having the difference frequency F,-F,5 of about
`code, or the like, or no code. may be added instead of the
`63.649475 MHz is the desired tracking injection frequency
`time-stamped code. The code-adding balanced mixer 38
`for the selected VHF channel 3. (It should be noted that the
`mixes the unmodulated, reconstructed video carrier signal
`difference between the video carrier frequency of 61.25
`having the frequency F,, with the injection signal having the
`MHzfor channel 3 and the frequency of about 63.649475
`frequency F,, in order to producefirst and second interme-
`MHzis about 2.399475 MHz, which is the frequency of the
`diate frequency encoded ancillary output signals having
`output of the oscillator 42.)
`corresponding sum and difference frequencies F,,+F,, and
`The tuner 24 preferably has a channel-select output 52
`Fy-Fy.
`(e.g., a control voltage which is applied to a varactor). The
`output of the balanced up converting mixer 50 is preferably
`The first and second intermediate frequency encoded
`ancillary output signals having the corresponding sum and
`filtered by a lowpass tracking filter 54 which is controlled by
`difference frequencies F,,+F,, and F,,-F,, are applied to a
`the channel-select output 52 from the tuner 24 to passsignals
`sideband strippingfilter 48. For an example of the frequen-
`at frequencies no more than five to ten MHz greater than the
`video carrier frequency of the selected television channel.
`cies which may be used by the receiving and encoding
`apparatus 10, the frequency F,, of the unmodulated, recon-
`Therefore,
`the second intermediate frequency tracking
`structed video carrier signal produced by the video carrier
`signal, which has the difference frequency F,.-F_ (i.e., the
`reconstruction circuit 32 will be 45.75 MHz,if the original
`ancillary signal) and whichis received from the balanced up
`input signal is exactly on frequency andif the local oscillator
`converting mixer 50, is passed through the lowpass tracking
`26 frequency is exactly 45.75 MHz abovethe input signal
`filter 54, and then through a controllable attenuation circuit
`frequency. Thus, if the oscillator 42 is set at 2.399475 MHz,
`56 and through a control switch 58 to a directional coupler
`the frequency of the first intermediate frequency encoded
`60. The control switch 58 is controlled by an injection
`ancillary outputsignal of the code-adding balanced mixer 38
`controller 62 in order to inject the ancillary signal at con-
`trollable times with reference to the television broadcast
`is about 48.149475 MHz and the frequency F,, of the
`second intermediate frequency encoded ancillary output
`signal. For example, the ancillary signal may be injected
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`5,629,739
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`7
`during the active video timeof line twenty-four in the NTSC
`television signal and suppressed at all other times. The
`directional coupler 60 injects the ancillary signal into the
`television broadcast signal from the splitter 22 for disiribu-
`tion to the first and second viewingsites 18 and 20. Thefirst
`intermediate frequency tracking signal having the sum fre-
`quency F,<+F,5, on the other hand,
`is blocked by the
`lowpass trackingfilter 54. Also, the channel-select output 52
`of the tuner 24 is connected to the encoder 44 permitting the
`encoder 44 to add a channel identifier to the injection signal
`which is supplied by the injection signal circuit 40 to the
`second input of the code-adding balanced mixer 38.
`Accordingly, because the ancillary signal which is sup-
`plied to the directional coupler 60 is locked to the output
`signal of the local oscillator 26 and to the unmodulated,
`reconstructed video carrier signal which has the frequency
`F,,. the ancillary signal tracks errors and offsets in both the
`frequency F,, of the signal provided by the local oscillator
`26 and in the received video carrier. Also, because the
`amplitude of the ancillary signal will generally be far higher
`than that of the received television signal, the controllable
`attenuation circuit 56 is preferably employed between the
`lowpass trackingfilter 54 andthe directional coupler 60. The
`signal attenuation introduced by the controllable attenuation
`circuit 56, which may be controllable by known means,
`ensures that the amplitude of the ancillary signal which is
`injected by the directional coupler 60 is matched to the
`amplitude of the corresponding received television broad-
`cast signal.
`Thefirst and second viewing sites 18 and 20 within the
`selected dwelling 12 may include, for example, correspond-
`ing television receivers 64 and 66 and corresponding decod-
`ers 68 and 70. In addition, the first viewing site 18 within the
`selected dwelling 12 may include, for example, a VCR 72.
`Asis knownin the audience measurementart, the ancillary
`signal is read by the decoder 68 from a video signal which
`is acquired by either the television receiver 64 or the VCR
`72 at the first viewing site 18 within the selected dwelling
`12, and the ancillary signal is read by the decoder 70 from
`a video signal which is acquired by the television receiver 66
`at the second viewing site 20 within the selected dwelling
`L.
`
`Theancillary signal may be a channel-recognition signal
`comprising a record which may contain the time ofinitial
`reception at the signal entrance 14 (e.g., as may be generated
`by the clock 46 operatively associated with the injection
`signal circuit 40), a datum (e.g., a serial number of the
`receiving and encoding apparatus 10 as may be added by the
`encoder 44) which uniquely identifies the signal source 16
`that was coded, and a datum indicative of the channel on
`which the encodedtelevision signal in question was received
`(as may be also added by the encoder 44 in response to the
`channel-select output 52). This record, which may be time-
`stamped by the appropriate decoder 68 or 70 at the time of
`viewing, is stored by a local controller 74 and is subse-
`quently forwarded via the public switched telephone net-
`work 76 to a central data collection office computer 78,as is
`knownin theart. Asis also knownin theart, having two time
`stamps on a viewing record allows both the time of record-
`ing and the time of viewing of programs recorded in the
`selected dwelling 12 on the VCR 72 to be identified.
`Some modifications and alterations of the present inven-
`tion have been described above. Other modifications and
`alterations of the present invention will occur to those
`skilled in the art. For example, although the receiving and
`encoding apparatus 10 is shown located within the selected
`dwelling 12, the receiving and encoding apparatus 10 may
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`So
`
`55
`
`60
`
`65
`
`8
`be located at any location in which it is convenient to inject
`an ancillary signal into a program signal. Also,although the
`ancillary signal is specifically shown in the drawing as being
`injected into a television program signal,
`it should be
`apparent that the ancillary signal may be injected into any
`program signal such as a radio program signal. It will be
`understood by those skilled in the art that the teachings of
`the present invention, although described in connection with
`NTSCtelevision signals, may be equally well applied to
`other broadcast television program signals (such as PAL and
`SECAM) and may be used with different conventional
`intermediate frequencies to determine corresponding
`selected frequencies. Also, although the drawing shows a
`single lowpassfilter for the lowpass trackingfilter 54, it will
`be understood by those skilled in the art that, in order to
`cover the approximately 800 MHz frequency range in which
`television program signals may be broadcast, a parallel array
`of lowpass tracking filters 54 may be used. Accordingly,it
`is intended that all such modifications and alterations be
`considered as within the spirit and scope of the invention as
`defined in the attached claims.
`I claim:
`1. A method for compatibly transmitting and receiving
`both a program signal and an ancillary signal within a
`frequency band normally occupied by the program signal
`alone, the program signal including a modulated carrier
`having a carrier frequency and a low energy density portion
`of the frequency band, the method comprising the following
`steps:
`receiving the program signal; and,
`selectively adding the ancillary signal at an injection
`frequency within the lower energy density portion of
`the frequency band so that the injection frequency is
`locked to the carrier frequency.
`2. The method of claim 1 wherein the step of selectively
`adding the ancillary signal comprises the step of selectively
`adding the ancillary signal at an injection frequency within
`the lower energy density portion of the frequency band so
`that the injection frequency is also locked to the frequency
`of a local oscillator.
`3. The method of claim 1 wherein the step of selectively
`adding the ancillary signal comprises the step of modulating
`the ancillary signal on the carrier so that the injection
`frequency is locked to the carrier frequency.
`4. A system for compatibly transmitting and receiving
`both a program signal and an ancillary signal within a
`frequency band normally occupied by the program signal
`alone, the program signal including a modulated carrier
`having a carrier frequency and a low energy density portion
`of the frequency band, the system comprising:
`areceiver which is arranged to receive the program signal,
`wherein the receiver has a local oscillator producing a
`local oscillator frequency; and,
`a signal injector which is arranged to selectively add the
`ancillary signal at an injection frequency within the
`lower energy density portion of the frequency band so
`that the injection frequency is locked to the local
`oscillator frequency.
`5. The system of claim 4 wherein the signal injector is
`arranged to selectively add the ancillary signal at an injec-
`tion frequency within the lower energy density portion of the
`frequency band sothat the injection frequency is also locked
`to the carrier frequency.
`6. The system of claim 4 wherein the signal injector
`comprises a mixer which is arranged to mix the injection
`frequency with the carrier frequency so that the injection
`frequency is locked to the local oscillator frequency.
`
`

`

`5,629,739
`
`9
`7. A system for compatibly transmitting and receiving a
`television program signal and an RF ancillary signal,
`wherein the television program signal is in a predetermined
`RF frequency band, and wherein the television program
`signal has a modulated video carrier signal and a low energy
`density portion of the frequency band, the system compris-
`ing:
`a tuner arranged to receive the television program signal,
`the tuner having as outputs a local oscillator signal and
`a modulated carrier signal;
`a first mixer arranged to mix an injection signal at a
`predetermined baseband injection frequency with a
`signal representative of the modulated carrier signal to
`produce an intermediate frequency injection signal;
`a second mixer arranged to mix the local oscillator signal
`with the intermediate frequency injection signal
`to
`produce the RF ancillary signal; and,
`a coupler arranged to couple the RF ancillary signal into
`the received television program signa