JPH044695A - Channel identification signal superimposing method for television sensor - Google Patents

Abstract

PURPOSE:To preclude the possibility of occurrence of beat disturbance in a simple way by superimposing a channel identification signal at a level not giving any hindrance to demodulation of an audio signal onto a frequency position symmetrical to an audio carrier frequency around a video carrier frequency. CONSTITUTION:Whether or not a channel identification signal appears to a signal at an output of a tuner 31 of a measurement object device 3 is monitored by a channel discrimination circuit 23 and a channel on which the channel identification signal is superimposed at a point of time when the channel identification signal appears is discriminated to be a reception channel. The channel information is recorded with time information or the like and regarded as part of a program rating measurement data. On the other hand, only a band required for broadcast reception is extracted from an output of a post amplifier 32 by a SAW filter 33 in the discrimination object device 3 and detected by a detection circuit 34. The audio signal of the television broadcast in an FM(frequency modulation) signal, and even when signals of same frequencies are overlapped in the FM signal, only a signal having a higher level is demodulated and a signal of a lower level is neglected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a channel identification signal superimposition method in a television sensor for measuring television audience ratings.

[Conventional technology]

In order to automatically measure television audience ratings, a device called a television sensor is generally attached to a sample device to be measured, such as a video tape recorder in a home, and information on whether the device is on or off and channel information is collected. etc., in relation to time information, and periodically collect it on a computer at the center using a telephone line.
are doing.

By the way, one effective method for collecting channel information is to superimpose a channel identification signal on the broadcast wave received by the receiving antenna and apply it to the antenna terminal of the device to be measured. Methods exist to determine the receiving channel by monitoring. That is, a channel identification signal is sequentially superimposed for each channel from channel 1 to channel 12, for example, at a predetermined frequency position within the band of each channel, for example, a position 5 MHz higher than the video carrier frequency. When a channel identification signal appears in the output signal of the tuner of the device, the channel on which the channel identification signal is superimposed at that time is determined to be the receiving channel.

[Problem to be solved by the invention]

The channel determination method described above has the advantage of stable operation compared to other channel determination methods, such as detecting the tuner's local oscillation signal and determining the channel from its frequency. The disadvantage is that beat interference occurs due to the superimposition of the identification signal, which adversely affects the received image and received sound.

In other words, in Figure 3 (al indicates the frequency allocation of broadcast waves in the NTSC system, f indicates the video carrier, f indicates the audio carrier, rsc indicates the color subcarrier, and the broken lines indicate the sidebands of the video signal. However, if a channel identification signal fcM is superimposed on 5 MHz from the video carrier frequency f such as bl in Fig. 3 (bl), the intermodulation distortion in the tuner of the device to be measured causes Various beats as shown (
spurious) occurs. This beat is mainly generated by the channel identification signal ftH and the audio carrier f5. Furthermore, at the stage where the output signal of the tuner is detected and converted to baseband, beats of lower frequency components are also generated as shown in FIG. , the audio carrier f, and the color subcarrier fsc.

On the other hand, in order to reduce the negative impact of these beat disturbances on received images and received audio, it is necessary to keep the level of the channel identification signal considerably low, or to perform channel identification within the vertical blanking period in synchronization with the broadcast wave. It is conceivable to superimpose the signals, but in the former case, considerable ingenuity is required in the detection unit to sufficiently detect the low-level channel identification signal, and in the latter case, the superimposition period of the channel identification signal Both methods have the disadvantage that they require a circuit section for control, making the device complicated.

The present invention has been proposed in view of the above points, and its object is to provide a method for superimposing a channel identification signal of a television sensor that is simple and does not cause any beat disturbance.

[Means to solve the problem]

In order to achieve the above object, the present invention superimposes a channel identification signal at a frequency position symmetrical to the audio carrier frequency around the video carrier frequency at a level that does not interfere with the demodulation of the audio signal.

[Effect]

In the channel identification signal superimposition method for a television sensor of the present invention, a channel identification signal of a level that does not interfere with the demodulation of the audio signal is superimposed at a frequency position symmetrical to the audio carrier frequency around the video carrier frequency. As a result, the only beats that occur within the band are those between the channel identification signal and the video carrier, and the beats occur overlapping with the audio carrier. Therefore, since no beat occurs in the sideband of the video signal, there is no adverse effect on the received video. Furthermore, due to the FM nature of the FM audio signal, low-level beats have no adverse effect on the received audio.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a television sensor to which the method of superimposing a channel identification signal for a television sensor of the present invention is applied. In FIG. 1, the television sensor 2 of this embodiment is connected between a receiving antenna 1 and an antenna terminal of a device to be measured 3 such as a television set, a video tape recorder, etc., and a tuner in the device to be measured 3. A detection signal is taken out from the output side of 31. That is,
The television sensor 2 includes a mixer 21 connected in series between the receiving antenna 1 and the antenna terminal of the measurement target bag W3;
The presence or absence of a channel identification signal is monitored from the signals obtained from the oscillator 22 which generates a channel identification signal to be superimposed on the broadcast wave received by the receiving antenna 1 and supplies it to the mixer 21, and the output side of the tuner 31 in the device to be measured 3. A channel determination circuit 2 that determines the reception channel of the bag W3 to be measured.
Contains 3. On the other hand, as the device 3 to be measured, only the part from the antenna terminal to the detection stage is shown, and a tuner 31, a post amplifier 32, a SAW filter 33, and a detection circuit 34 are sequentially connected.

The tuner 31 also includes an RF amplifier 311 and a mixer 31.
2, an oscillator 313, and an output LC circuit 314.

FIG. 2 shows the frequency allocation of the signals of the respective parts denoted by the same symbols a to e in the embodiment of FIG. 1.

The operation of the embodiment will be described below with reference to FIGS. 1 and 2.

The broadcast waves received by the receiving antenna 1 are sent to the TV sensor 2.
In the mixer 21 within the oscillator 22, the channel identification signal generated by the oscillator 22 is sequentially superimposed for each channel. Here, the channel identification signal has a video carrier frequency f as shown in FIG. 2 (bl) for a broadcast wave as shown in FIG. 2 (al).

The frequency position is symmetrical to the audio carrier frequency f, that is, the frequency position is 4°5 MHz lower than the video carrier frequency f, and is at a level that does not interfere with the demodulation of the audio signal. As a concrete level, the voice carrier f
, it is sufficient to select a value approximately 30 dB lower than .

Next, the broadcast wave on which the channel identification signal feH has been superimposed is amplified by the RF amplifier 311 in the tuner 31 of the device to be measured 3, and at this time, due to intermodulation distortion,
Beats with frequency components that are integral multiples and their sum difference occur, but in this case, the beats that occur within the band are:
FIG. 2 (as shown in C1, the channel identification signal fe1
1 and video carrier f.

, and the beat will overlap with the audio carrier f.

Next, the broadcast wave is amplified by an RF amplifier 311, and then mixed with a local oscillation signal generated by an oscillator 313 and a mixer 312.
By mixing the signals at , the frequency is converted into a band centered around a certain video intermediate frequency (58, 75 MHz), and the output is taken out via the output LC circuit 314 .

The frequency allocation of this signal is shown in FIG. 2 (dl), but because of the upper heterodyne system, the frequency height is inverted from that of FC+ in FIG. 58.75 + 4.5
The channel identification signal at the MHz position is 10dB
It will be somewhat attenuated. Note that there is no problem in detecting the channel identification signal even if the channel identification signal is attenuated to this extent.

Here, the output signal of the output LC circuit 314 or the signal of the output stage of the post amplifier 32 is taken out by the television sensor 2, and the reception channel of the measurement target device 3 is determined from the presence or absence of the channel identification signal at the 58.75+4.5MHz position. It will be judged. That is, the oscillator 2 of the television sensor 2
2, a channel identification signal is sequentially superimposed on each channel, but during this process, the channel determination circuit 23 monitors whether or not a channel identification signal appears in the output side signal of the tuner 31 of the device to be measured 3. It is determined that the channel on which the channel identification signal is superimposed at the time when the channel identification signal appears is the receiving channel. This channel information is recorded together with time information, etc., and is considered as part of the audience rating measurement data.

On the other hand, in the measurement target bag [3, only the band necessary for broadcast reception is extracted from the output of the post amplifier 32 by the SAW filter 33, and detected by the detection circuit 34. Figure 2 t
el indicates the frequency allocation of the signal at the output stage of the SAW filter 33, and the broken line indicates the specification of the SAW filter 33.

Here, the audio carrier has overlapping beats generated by the channel identification signal and the video carrier, but the audio of television broadcasting is FM (frequency modulation), and in FM, even if signals of the same frequency overlap, the level is high. The channel identification signal, which is superimposed at an appropriately lowered level, has no effect on the received audio at all because it has a so-called predatory-feeding property in which only signals at low levels are demodulated and low-level signals are ignored. . Furthermore, since no other beats occur within the band, there is no effect on the received video.

〔Effect of the invention〕

As explained above, in the TV sensor channel identification signal superimposition method of the present invention, a channel at a frequency position symmetrical to the audio carrier frequency with the video carrier frequency at the center is set to a level that does not interfere with the demodulation of the audio signal. By superimposing the identification signal, the only beats that occur within the band are those between the channel identification signal and the video carrier, and the beats also overlap with the audio carrier. ■ Sideband of the video signal Since no beat occurs within the
There is no negative effect on the received video at all.

- Due to the predatory nature of FM audio signals, low-level beats have no negative effect on the received audio.

There are other effects.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a television sensor to which the channel identification signal superimposition method for a television sensor of the present invention is applied, FIG. 2 is an explanatory diagram of frequency allocation in each part of FIG. 1, and FIG. FIG. 2 is an explanatory diagram of conventional frequency allocation. In the figure, 1...... Receiving antenna 2... TV sensor 21... Mixer 22... Onrator 23... Channel determination circuit 3...Device to be measured 31...Tuner 311...RF amplifier 312...Mixer 313...Oscillator 314...Output LC circuit 32... ... Post amplifier 33 ... SAW filter 34 ... Detection circuit

Claims (1)

[Claims] A channel identification signal superimposition method for a television sensor, characterized by superimposing a channel identification signal at a level that does not interfere with demodulation of an audio signal at a frequency position symmetrical to an audio carrier frequency with the video carrier frequency as the center.