GB2062386A

GB2062386A - Intercarrier sound separation networks

Info

Publication number: GB2062386A
Application number: GB8034173A
Authority: GB
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1979-10-26
Filing date: 1980-10-23
Publication date: 1981-05-20
Also published as: AU3776985A; GB2062386B; IT8025565A0; AU6349680A; AT386310B; AU539824B2; ATA526780A; IT1134029B; DE3040250C2; FR2469070B1; AU562128B2; FR2469070A1; DE3040250A1

Abstract

In a signal separation network functioning both as a trap circuit for intercarrier sound signal in a video signal path from a video detector 208 to video processing circuitry 280, and an output for sound processing circuitry 290, first 233 and second 232, 234 signal paths are coupled between detector 208 and video processing circuitry 280, the second signal path includes a first reactive impedance element 232, 234 of one sign, a third signal path 235 to ground is coupled to the second signal path and includes a second reactive impedance element 238 of an opposite sign and the signal developed across the third signal path is coupled to the input of the intercarrier sound signal processing circuitry 290. The three signal paths comprise a tuned circuit 230 tuned to exhibit a transfer function having a zero within a given range of frequencies occupied by the intercarrier sound signals at the input of the video processing circuitry 280 and exhibiting a pole within the given range of frequencies at the junction of the third signal path and the coupled input of the sound processing circuitry 290. <IMAGE>

Description

SPECIFICATION Signal separation networks This invention relates to signal separation networks and, in particular, to tuned circuit networks which composite video and intercarrier sound signals from a common signal path in a television receiver.

In color television receivers of the intercarrier sound variety, the sound and picture intermediate frequency signals may be amplified in a common signal processing stage. The composite video signal is then detected in an amplitude modulation detector, and an intercarrier sound signal is detected by mixing the picture carrier and the frequency-modulated sound carrier.

A synchronous demodulator may be used for the simultaneous detection of both the composite video and intercarrier sound signals. This is due to the substantially linear operation of the synchronous demodulator, which prevents undesired intermodulation of the intercarrier sound and color subcarrier signals during the detection process. The synchronous demodulator will thus produce both the composite video signal and the intercarrier sound signal at a singie output terminal.

Following the common detection of the composite video and intercarrier sound signals, it is necessary to separate the two signals so that the sound and video information may be further processed and reproduced. The intercarrier sound signal must be removed from the video signal to prevent possible intermodulation of the video and intercarrier sound signals during the processing of the composite video signal. Similarly, the video information must be eliminated from the intercarrier sound signal to prevent the generation of intermodulation and harmonic distortion in the sound channel.

In typical arrangements of the prior art, the detected intercarrier sound and video signals are coupled to the sound processing circuitry by a sound take-off network. The sound take-off network may exhibit a certain amount of selectivity at the intercarrier sound frequency so as to suppress the video signal components relative to the intercarrier sound signal. The intercarrier sound signal is then usually applied to a bandpass filter, which further attenuates the video signal components. The resultant bandpassed signal can then be processed without undesirable intermodulation of the video and intercarrier sound signals.

The detected intercarrier sound and video signals are also coupled to the luminance and chrominance processing circuits by way of a signal path which includes an intercarrier sound trap circuit. The video signals may then be processed without the generation of undesirable intermodulation between the sound and video signals, one form of which is the visible beat pattern caused by intermodulation of the intercarrier sound and chrominance subcarrier signals.

A particular type of network which is well suited for the intercarrier sound trap is the "bridged-T" network. One form of this network is characterized by a parallel resonant circuit in series with the video signal path, and an impedance in shunt with the video signal path.

The shunt impedance is used to balance the parallel resonant circuit, so as to effect maximum cancellation at the intercarrier sound frequency. In a second form of the network, a parallel R-C circuit in series with the video signal path is tuned and balanced by reactive and resistive impedances in the shunt leg. In both forms, the network is known as a cancellation-type network, since signals at the tuned frequency at the output junction of the two parallel circuit paths are in an antiphase relationship and hence trapped out of the video signal path. An example of the use of a bridged-T network of the first form as an intercarrier sound trap is shown in U.S. Patent 2,81 1,580, issued to Jack Avins.The Avins arrangement provides an additional feature, in that the intercarrier sound signal is inductively coupled from the parallel resonant circuit of the network for application to the sound processing circuitry.

In accordance with the principles of the present invention, a signal separation network is provided which functions as both a trap circuit for the intercarrier sound signal in the video signal path, and a take-off network for the sound processing circuitry. A detector is provided for producing detected video frequency and intercarrier sound signals the intercarrier sound signals occupying a given range of frequencies exclusive of the video frequency components. First and second signal paths are coupled between the output of the detector and the input of video processing circuitry, the second signal path including a first reactive impedance element of one sign.

A third signal path is coupled between the second signal path and the input of the sound processing circuitry and includes a second reactive impedance element of an opposite sign. The signal developed across the third signal path is coupled to the input of the intercarrier sound signal processing circuitry. The three signal paths comprise a tuned circuit tuned to exhibit a transfer function having a zero within the given range of frequencies at the input of the video processing circuitry, and exhibiting a pole within the given range of frequencies at the junction of the third signal path and the input of the sound processing circuitry.

In accordance with further principles of the present invention the third signal path is coupled between the second signal path and the input of a bandpass filter, the bandpass filter being tuned to the intercarrier sound signal frequency, having an input, and an output coupled to the input of the sound processing circuitry. A fourth signal path is coupled between the junction of the third signal path and the input of the bandpass filter and a point of reference potential, and has an impedance which is isgnificantly less than the impedance of the third signal path at the intercarrier sound signal frequency. The four signal paths comprise a tuned circuit which attenuates the intercarrier sound signal at the input of the video processing circuitry. The network is tuned by varying a single adjustable inductor in the shunt leg of the network.

A ceramic filter may be employed as the bandpass filter at the input to the sound processing circuitry. In that instance, the fourth signal path comprises a resistive impedance element which is effectively in shunt with the input impedance of the ceramic filter. A bridged-T network is thereby configured so as to provide a relatively broad and deep trap at the intercarrier sound signal frequency at the input to the video processing circuitry, and the ceramic filter is driven from a sufficiently low impedance to provide a relatively high input signal level to the ceramic filter and the sound processing circuitry.

It has been found that video signals at two frequencies are especially troublesome in the sound channel. Signals in the vicinity of the color subcarrier frequency can intermodulate with the intercarrier sound signal to cause low frequency interference in the sound channel, and video signals at half the intercarrier sound frequency can create harmonic distortion interference. In accordance with a further aspect of the present invention, the signal separation network is arranged to provide trapping at the color subcarrier frequency at the junction on the third signal path so as to substantially remove signals about this-frequency from the intercarrier sound signal. The signal separation network may also be arranged to provide trapping at the halfintercarrier sound frequency at this junction.The network may be further arranged to provide attenuation at the junction for both these frequencies by locating a zero in the transfer function at a frequency intermediate these two troublesome frequencies.

Alternatively, a simple LC circuit, tuned to the intercarrier sound frequency, may be used as the bandpass filter. The LC tuned circuit has been found to have decreased rejection at the color subcarrier frequency.

In this configuration, the fourth signal path comprises a reactive impedance element which provides increased rejection of the color subcarrier signal at the intercarrier sound take-off point. The bridged-T network is arranged to provide a desired driving impedance for the LC tuned circuit as well as improved color subcarrier rejection. The resulting combination provides a higher level input signal to the sound processing circuitry than the ceramic filter embodiment, which improves the sound-quieting performance of the television receiver.

In the drawings: FIGURE 1 illustrates, partially in block diagram form and partially in schematic diagram form, a signal separation network arranged in a bridged-T configuration in accordance with the principles of the present invention: FIGURES 2a and 2b are S-plane plots illustrating transfer functions of the signal separation network of FIGURE 3; FIGURE 3 illustrates, partially in schematic diagram form and partially in block diagram form, a signal separation network arranged in a bridged T configuration in accordance with the principles of the present invention which attenuates mid- band video signals in the intercarrier sound signal path; FIGURE 4 is an S-plane plot illustrating a transfer function of the signal separation network of FIGURE 3.

FIGURE 5 illustrates, partially in block diagram form and partially in schematic diagram form, a signal separation network constructed in accordance with the principles of the present invention to drive a ceramic bandpass filter in the sound channel; FIGURES 6a and 6b illustrate response curves of the network of FIGURE 5.

FIGURE 7 illustrates in schematic diagram form an equivalent circuit of the signal separation network of FIGURE 5; and FIGURE 8 illustrates, partially in block diagram form and partially in schematic diagram form, a signal separation network constructed in accordance with the principles of the present invention to drive a discrete bandpass filter in the sound channel.

Referring to FIGURE 1, a signal separation network 230 is shown coupled to the signal path between a detector 208 and video processing circuitry 280. The output signal E1 of the detector 208 comprises a composite video signal and an intercarrier sound signal. This output signal is applied to the base of an emitter follower coupled transistor 210, which may, for instance, be the output stage of the detector 208. The output signal at the emitter of the transistor 210 is applied to the input of video processing circuitry '280, which processes the composite video signal E2 for display on a cathode ray tube (not shown).

The resistor 212 represents the source impedance seen by the signal separation network 230 and the video processing circuitry 280.

The separation network 230 is arranged in a bridge-T configuration in accordance with the principles of the present invention. The separation network 230 comprises a bridging resistor 233 coupled between source impedance 212 and point 21 9 at the input of video processing circuitry 280. Coupled in parallel with resistor 233 are series-coupled capacitors 232 and 234. An inductor 238 and a resistance 239 are coupled in series between point 235, which is the junction point of capacitors 232 and 234, and a point of reference potential (ground). The resistance 239 represents the coil losses of inductor 238, or may be a discrete resistor. The intercarrier sound signal is coupled to the sound processing circuitry 290 from point 235.

The operation of the signal separation network 230 may be understood by referring to the Splane plots of FIGURE 2a and 2b. An S-plane plot, sometimes referred to as a pole-zero pattern or constellation, is a diagramatic representation of the analytic properties of a function expressed in the complex plane. The poles of the function are identified by small crosses and the zeros identified by small circles. The signal separation network may be described mathematically by transfer functions which represent the effects of the network at points 219 and 235. The transfer function at point 21 9 is the ratio of the composite video signal E2 to the detected signal E" and is a mathematical expression containing zeroes in its numerator and poles in the denominator.

Similarly, the transfer function at point 235 is the ratio of the signal E3 to E. The poles and zeroes of the respective transfer functions are shown in FIGURES 2a and 2b, respectively.

In FIGURE 2a, the transfer function at point 219 exhibits the pole pair 72, 74 on the intercarrier sound frequency circle 50 to the left of the jw axis and the zero pair 76, 78 at the intersection of circle 50 with the jii axis. The location of the zero pair 76, 78 is controlled by properly proportioning the resistance of the parallel circuit elements with the resistance of the shunt leg circuit elements. Due to its closer proximity to the jco axis, the zero 76 will predominate over pole 72, and its location on the jw axis indicates virtually infinite attenuation at that frequency. Therefore, at point 219, the separation network 230 will act as a virtually infinite Q trap, sharply attenuating the intercarrier sound signal in the video signal path to the video processing circuitry 280.

At point 235, the intercarrier sound take-off point of the separation network 230, FIGURE 2b shows the location of the same pole pair 72, 74 as in FIGURE 2a. The pole 72 will dominate at the intercarrier sound frequency (the intersection of circle 50 with the jw axis), thereby peaking the response at point 235 at the intercarrier sound frequency. The zeroes 82, 84 in FIGURE 2b are seen to be located at the origin, which indicates sharp attenuation of very low frequency signals.

Thus, the response at point 235 will be peaked about the intercarrier sound frequency and will roll off toward maximum attenuation at D.C.

The separation network 231 of FIGURE 3 is identical to that of FIGURE 1, with the exception of the addition of capacitor 236, which is coupled in series between point 235 and inductor 238.

Separation network 231 exhibits the same transfer function at point 21 9 as the network 230 of FIGURE 1, the poles and zeroes of which are shown in FIGURE 2a. However, the inclusion of capacitor 236 results in a relocation of the zeroes of the transfer function at point 235, as shown in FIGURE 4. There it is seen that zeroes 86 and 88 are located on circle 60, which intersects the jo axis in the middle of the video frequency range. By proper selection of the value of capacitor 236, zeroes 86, 88 and the circle 60 can be located at the color subcarrier frequency, half the intercarrier sound frequency or at some intermediate frequency.

These locations will result in maximum attenuation at those frequencies which are sources of interfering signals in the sound channel.

Therefore, it may be seen that the separation network 231 of FIGURE 3 provides high, virtually infinite Q trapping of the intercarrier sound signal in the video signal path at point 219, and a peaked response about the intercarrier sound frequency at the sound take-off point 235, with substantial attenuation of those color subcarriers and/or midband video signals which cause intermodulation and harmonic distortion in the sound channel.

Referring to FIGURE 5, a detector 10 is shown which produces detected video and intercarrier sound signals at its output. The output of the detector 10 is coupled by way of a series inductor 12 to a bridged-T network 30. A resistor 16 and a capacitor 14 are coupled from the junction of the inductor 12 and the bridged-T network 30 to a point of reference potential (ground). The resistor 1 6 is a load impendance for the detector 10, and the inductor 12 and the capacitor 14 cooperate to suppress harmonics of the video carrier signal at the detector output. These harmonics would otherwise be coupled back into the radio frequency section of the television receiver, producing interference which is commonly known as "channel 8 beat".

The bridged-T network acts to cancel the intercarrier sound signal from the signals which appear at a terminal 37. The remaining video signals are then coupled to video processing circuitry 22 by a series resistor 1 8 and an emitter follower coupled transistor 20.

The bridged-T network 30 includes a bridging resistor 36 and serially-coupled capacitors 32 and 34, which are coupled in parallel in the signal path between the detector 10 and the video processing circuitry 22. The serial combination of an adjustable inductor 38 and a resistor 40 is coupled between the junction of capacitors 32 and 34 and a point of reference potential (ground).

The intercarrier sound signal is developed by the bridged-T network 30 at the junction 39 of inductor 38 and resistor 40, and is coupled to the input of a ceramic filter 50. The bandpassed intercarrier sound signal is coupled to an input of a limiter and FM detector circuit 60, which processes the sound information for audio reproduction. A resistor 52 is coupled in shunt with the signal path at the output of the ceramic filter, which matches the output impedance of the filter. The remaining end of the resistor 52 is bypassed to ground by a capacitor 54.

The bridged-T network 30 is tuned to the intercarrier sound frequency by adjustment of inductor 38, and exhibits a trap response at terminal 37 and a peak response at junction 39 as shown in FIGURES 6a and 6b. Waveform 82 of FIGURE 6a illustrates the response at terminal 37, with maximum attenuation occurring at the intercarrier sound frequency (4.5 MHz in the NTSC television system). Waveform 84 of FIGURE 6b shows the peaked response at the intercarrier sound frequency at junction 39.

In addition to the tuning of the bridged-T network, it is also necessary to ensure that the intercarrier sound signals, which are coupled to the ceramic filter 50, are of a sufficiently high level, and at an impedance level which is consistent with the input requirements of the ceramic filter. In the embodiment of the invention which is shown in FIGURE 5, the ceramic filter 50 is assumed to have an input and an output impedance of 1,000 ohms, and the center frequency of the ceramic filter passband (the intercarrier sound frequency) is assumed to be 4.5 MHz. In the following example, these values will be used to illustrate the selection of proper element values for the bridged-T network of FIGURE 5.

The operation of the bridged-T network may be understood by referring to the bridged-T equivalent circuit shown in FIGURE 7. The network is driven by an idealized current source 100 and a series impedance 102. Resistances 110 and 114 are coupled in series with the video signal path, and each resistance is in parallel with one of capacitances 112 and 11 6 respectively. The series combination of resistance 120, capacitance 122, inductance 124, and resistance 126 is coupled between the junction 11 3 of resistances 110 and 114 and ground. A capacitance 118 is coupled in parallel with the resistance 120.

Resistances 110, 114 and 120 have values which are a function of the value of the bridging resistor 36 in FIGURE 5. Resistances 110 and 114 are each half the resistance of resistor 36, and resistance 120 has a negative resistance of onefourth of the value of resistor 36. Capacitances 112, 116 and 118 have values which are related to the values of capacitors 32 and 34 of FIGURE 1.

These capacitances are drawn in broken lines because they are each shunted by relatively much smaller impedances. For purposes of this example, these broken line capacitances may be neglected.

Capacitor 122 has a value which is equal to the sum of the values of capacitors 32 and 34 in FIGURE 5. Inductance 124 represents the inductance of inductor 38, and resistance 126 represents the value of resistor 40 plus the coil losses of inductor 38.

When the bridged-T network is properly tuned, capacitance 122 and inductance 124 present virtually a zero impedance to signals at the intercarrier sound frequency. The impedance of the series path between junction 113 and ground is then determined by the effect of resistances 120 and 126. When the value of resistance 126 is chosen to be equal to the negative resistance of resistance 120, the two resistances cancel each other, and a virtual short circuit is presented by the series path to intercarrier sound signals at junction 11 3. By selecting component values in this manner, the bridged-T network trap response at terminal 37 of FIGURE 5 will have virtually an infinite Q at the intercarrier sound signal frequency, resulting in virtually complete elimination of the intercarrier sound signal from the signals which are applied to the video processing circuitry.Thus, it is seen that the network 30 of FIGURE 5 is properly proportioned when the value of resistor 40 plus the losses of inductor 38 is equal to one-fourth the value of the bridging resistor 36.

When the bridged-T network 30 of FIGURE 5 was initially constructed and analyzed, the junction 39 at which the ceramic filter was connected was located at the opposite end of inductor 38 at the junction of capacitors 32 and 34 (such as point 235 as shown in FIGURES 1 and 3). It was found that, in the FIGURES 1 and 3 configurations, the input impedance of the ceramic filter 50 was in parallel with the inductor 38 and the resistor 40, causing the shunt leg of the bridged-T network to have a complex impedance characteristic. This complex impedance resulted in a degradation of the Q of the network which adversely affected both the video and sound channels. The lower Q caused a broadening of the bandwidth of the intercarrier sound trap 82 at terminal 37.The trapping effect was found to extend into the frequency range of the color subcarrier information, thereby adversely affecting chrominance reproduction. Similarly, the lower 0 at the junction of capacitors 32 and 34 resulted in a broadening of the passband 84 at the input to the ceramic filter, which caused a decrease in the rejection of the color subcarrier in the sound channel and increased intermodulation distortion of the color subcarrier and intercarrier sound signals.

In accordance with an embodiment of the present invention, the ceramic filter 50 is coupled at junction 39 as shown in FIGURE 5. The resistive impedance of the shunt leg is simply calculated as the sum of the coil losses of the inductor 38 and the parallel resistance of resistor 40 and the input resistance of the ceramic filter 50. The resistive impedance of the shunt leg in the example shown in FIGURE 5 is approximately 200 ohms, which is seen to be one-fourth the value of the bridging resistor 36, as explained in conjunction with FIGURE 7. The bridged-T network 30 thus has a high 0, which results in a deeper and narrower trapping effect at terminal 37: The high Q also improves the selectivity of the bandpass effect for the intercarrier sound signal at junction 39, which has a steeper skirts than the initial configuration discussed above.

It may also be noted that the ceramic filter 50 is driven by an impedance which is lower than the 1 K input impedance of the ceramic filter. This lower driving impedance advantageously provides the high 0 in the bridged-T network and consequently a higher level signal is supplied to the ceramic filter 50. The mismatched impedances at the input to the ceramic filter do result in a slight amplitude "tilt" across the passband of the ceramic filter, which has been found to cause a few degrees of phase distortion in the detected sound signal.

However, this small amount of distortion is negligible by comparison with the hundreds of degrees of phase modulation of the FM sound signal, and is greatly overshadowed by the effective elimination of color subcarrier intermodulation distortion in the sound channel achieved by the arrangement of FIGURE 5.

FIGURE 8 illustrates an embodiment of the present invention which includes a bridged-T network 44 and an intercarrier sound band pass filter 70. The remaining elements of FIGURE 8 are identical to the comparable elements of FIGURE 5 and bear the same reference numerals. The network 44 differs from the network 30 of FIGURE 5 in that an additional inductor 42 is coupled in the shunt leg between resistor 40 and the point of reference potential (ground), and the intercarrier sound take-off point is located at the junction of resistor 40 and inductor 42. The junction 39 at the intercarrier sound take-off point is coupled to a parallel LC filter 70, including a capacitor 74 and a tapped inductor 76, by a capacitor 72. The other end of the parallel LC filter 70 is coupled to ground by bypass capacitor 54.The intercarrier sound signal is coupled to the limiter and FM detector 60 from the tap of the inductor 76.

The parallel LC filter 70 is tuned to the intercarrier sound signal frequency so as to provide a bandpassed input signal for the limiter and FM detector 60. It has been found that the LC filter 70 has a broader passband than the ceramic filter 50 of FIGURE 5, which results in a decrease in the rejection of the color subcarrier signal in the sound channel. The inductor 42 of the bridged-T network 44 is coupled in parallel with the input of the LC filter 70. This inductor provides a low impedance path to ground for lower frequency signals at junction 39, which results in improved color subcarrier rejection in the bandpass response at the junction 39. The arrangement of FIGURE 8 has been constructed and tested and found to have a color subcarrier signal level at the input to the limiter and FM detector 60 which is 20 to 30 db lower than the intercarrier sound signal level at that point.

In the example of FIGURE 8, the value of resistor 40 is illustratively shown as 1 50 ohms.

The shunt leg of the bridged-T network 44 has a resistive impedance of approximately 200 ohms, which is approximately one-fourth the value of the bridging resistor 36. The network 44 thus exhibits a high Q trapping response 82 at terminal 37 and a peaked, narrow passband 84 at the intercarrier sound signal take-off junction 39.

The arrangement of FIGURE 8 also provides a higher level intercarrier sound signal to the input of the limiter and FM detector 60 than the arrangement of FIGURE 5. It has been found that the intercarrier sound signal experiences approximately a 13 db loss between the output of the detector 10 and the input of the limiter and FM detector 60 in FIGURE 5, which is largely due to the 6 db loss imparted to the signal by the ceramic filter. By comparison, the intercarrier sound signal experiences only a 2 db loss between the output of the detector 10 and the input of the limiter and FM detector 60 in the arrangement of FIGURE 8, which is due to a 5-6 db gain imparted to the signal by the LC filter.

The LC filter arrangement of FIGURE 8 further provides an improvement in ease of assembly as compared to the arrangement of FIGURE 5. For instance, the capacitors 72 and 74 and the tapped inductor 76 may be manufactured as a single unitized package, allowing their assembly in one step in the construction of the circuit of FIGURE 8.

Thus, only two unitary elements, the filter 70 and the capacitor 54, are assembled in the arrangement of FIGURE 8, compared with three elements, the ceramic filter 50, the resistor 52, and the capacitor 54, in the arrangement of FIGURE 5. The network 44 similarly lends itseif to combining elements as unitary assemblies, such as the combination of inductor 38 and capacitors 32 and 34.

Claims

1. In a television receiver having a common detector for producing, at an output, detected video frequency signal components and an intercarrier sound signal occupying a given range of frequencies exclusive of said video frequency signal components, means, having an input terminal, for processing said video frequency signal component, and means, having an input, for processing said intercarrier sound signal; a network for separating said video and intercarrier sound signal component comprising first and second parallel signal paths coupled between the output of said detector and the input terminal of said video signal processing means and including a reactive impedance element of one sign; a third signal path including a reactive impedance element of an opposite sign, coupled between an intermediate point on said second signal path and a point of reference potential, and means for coupling the signal developed across said reactive impedance element in said third signal path to the input of said intercarrier sound signal processing means, said first, second and third signal paths comprising a tuned circuit tuned to exhibit a transfer function having a zero within said given range of frequencies at said input terminal, and exhibiting a pole within said given range of frequencies at the junction of said third signal path and said coupling means.

2. Apparatus according to Claim 1 wherein said video frequency signal components occupy a second given range of frequencies, and said third signal path further includes means for producing á minimum response at a frequency included within said second given range of frequencies at said junction.

3. Apparatus according to Claim 1 , wherein said video frequency signal components occupy a second given range of frequencies including a color subcarrier frequency, and that portion of said third signal path which is coupled between the junction of said coupling means and said third signal path and said point of reference potential is tuned to provide attenuation at approximately said color subcarrier frequency at said junction.

4. Apparatus according to Claim 1, wherein said video frequency signal components occupy a second given range of frequencies including a frequency which is half the frequency of said intercarrier sound signal, and that portion of said third signal path which is coupled between the junction of said coupling means and said third signal path and said point of reference potential is tuned to provide attenuation at approximately said half intercarrier sound signal frequency at said junction.

5. In a television receiver having a common detector for producing, at an output, detected video frequency signal components and an intercarrier sound signal occupying a given frequency range, means, having an input terminal, for processing said video frequency signal components, and means having an input, for processing said intercarrier sound signal; a bridged-T network for separating said video and intercarrier sound signal components comprising: a first signal path, including a resistive impedance, and a second signal path, including a first reactive impedance of one sign, coupled in parallel between the output of said detector and the input terminal of said video signal processing means; a third signal path, including a second reactive impedance of an opposite sign, coupled between said second signal path and a point of reference potential, and having a terminal at which said intercarrier sound signal is developed, and means for coupling said third signal path terminal to the input of said intercarrier sound signal processing means, wherein said first, second, and third signal paths comprise a tuned circuit for attenuating said intercarrier sound signal at the input terminal of said video signal processing means and for peaking the response at said third signal path terminal at a frequency within said given frequency range.

6. Apparatus according to Claim 5, wherein said video frequency signal components occupy a second given range of frequencies, and said third signal path includes a third reactive impedance serially coupled between said third signal path terminal and said point of reference potential, wherein that portion of said third signal path which is coupled between said third signal path terminal and said point of reference potential comprises a circuit which is tuned to produce a point of maximum attenuation at said third signal path terminal at a frequency which is included within said second given range of frequencies.

7. In a television receiver having a common detector for producing, at an output, detected video frequency signal components and an intercarrier sound signal having a given center frequency, means, having an input terminal, for processing said video frequency signal components; means, having an input, for processing said intercarrier sound signal; and a bandpass filter tuned to said intercarrier sound center frequency, exhibiting a given input impedance, and having an input, and an output coupled to the input of said intercarrier sound signal processing means; a network for separating said video and intercarrier sound signal components comprising: a first signal path coupled between the output of said detector and the input terminal of said video signal processing means; a second signal path coupled in parallel with said first signal path and including a first reactive impedance element of one sign; a third signal path, including a second reactive impedance element of an opposite sign, coupled between said second signal path and the input of said bandpass filter; and a fourth signal path coupled between the junction of said third signal path and the input of said bandpass filter and a point of reference potential and having an impedance which is substantially less than the impedance of said third signal path and the given input impedance of said bandpass filter at said intercarrier sound center frequency, such that the input impedance of said bandpass filter has substantially no effect on the response of said network at said input terminal, wherein said first, second, third and fourth signal paths comprise a tuned circuit for attenuating said intercarrier sound signal at said input terminal.

8. Apparatus according to Claim 7 wherein: said first signal path includes a resistive impedance element having a resistance which is substantially equal to four times the sum of the resistive impedances of said third and fourth signal paths.

9. Apparatus according to Claim 7, wherein: said bandpass filter comprises a ceramic filter.

10. Apparatus according to Claim 9, wherein: said fourth signal path comprises a resistive impedance element and wherein said sound reactive impedance element of said third signal path and said resistive impedance element of said fourth signal path are serially coupled in that order between said second signal path and said point of reference potential.

1 Apparatus according to Claim 7, wherein: said bandpass filter comprises a parallel LC circuit.

12. Apparatus according to Claim 11, wherein: said third signal path further includes a resistive impedance element and said fourth signal path comprises an inductive impedance element, and wherein said second reactive impedance element, said resistive impedance element and said inductive impedance element are serially coupled in that order between said second signal path and said point of reference potential.

13. Apparatus according to Claim 10 or 12, wherein: said second reactive impedance element comprises an adjustable reactive impedance element for tuning said tuned circuit.

14. In a television receiver having a common detector for producing, at an output, detected video frequency signal components and an intercarrier sound signal having a given frequency, means, having an input terminal, for processing said video frequency signal components; means, having an input, for processing said intercarrier sound signal; and a bandpass filter, tuned to said intercarrier sound frequency and having an input and an output coupled to the input of said intercarrier sound signal processing means; a network for separating said video and intercarrier sound signal components comprising: first and second parallel signal paths coupled between the output of said detector and the input terminal of said video signal processing means; a third signal path, including a reactive impedance element and a resistive impedance element, coupled between said second signal path and a point of reference potential; and means, independent of said reactive impedance element, for coupling said resistive impedance element of said third signal path in parallel with the input of said bandpass filter, wherein said first, second, and third signal paths comprise a tuned circuit for attenuating said intercarrier sound signal at said input terminal.

1 5. Apparatus according to Claim 14 wherein said coupling means, independent of said resistive impedance element, couples said reactive impedance element of said third signal path in.

parallel with the input of said bandpass filter.

1 6. A television signal separation circuit substantially as hereinbefore described with reference to Figure 1, Figure 3, Figure 5 and 7 or Figure 8 of the accompanying drawings.