JPH021985Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention consists of a filter in a television receiver, such as an IF (intermediate frequency) filter, by a group of narrowband filters that have a certain relationship, thereby reducing residual sidebands. The aim is to effectively remove interfering signals mixed into AM-transmitted television signals, thereby improving the received image quality.

(Prior art) Television signals transmitted using vestigial sideband amplitude modulation (AM) are often mixed with interference waves.
When interference radio waves mix into the same frequency band as the transmitted television signal frequency band, a beat (striped pattern) appears on the receiving screen, which significantly degrades the received image quality.

Conventionally, various methods have been taken as countermeasures against the incorporation of the above-mentioned jamming waves, and broadly speaking, countermeasures have been taken using receiving antennas and countermeasures using trap circuits within the receiver.

As countermeasures using receiving antennas, there are two methods: one that utilizes the directional characteristics of the receiving antenna in the horizontal plane, and the other that uses diversity reception. The former method using directional characteristics is effective when there is a difference in direction between the directions of arrival of the desired wave D and the interfering wave U, but when there is not much difference in direction, a multi-element antenna with good directivity must be used. First, there are limits to the selection of antennas, which increases the cost of receiving equipment. The diversity reception method can produce an improvement effect by installing two antennas with the same characteristics as shown in Figure 1 and combining them so that the desired waves are in the same phase and the interfering waves are in opposite phases. . In other words, in Figure 1, L (the distance between the two antennas) is set to satisfy the following conditions: M = (wavelength of interference wave) × (n + 1/2) L = (wavelength of interference wave) × (n + 1/2) / sinθ All you have to do is choose. Here, n is an integer, and θ is the angle formed by the directions of arrival of the D wave and the U wave. However, in order to satisfy the above conditions, the outputs of both antennas obtained with the same electric field and the same gain must be combined using the same feed line, which is technically complicated and increases the cost of the receiving equipment. It also leads to

Next, various traps or filters have been devised as countermeasures using the trap circuit in the receiver, each of which has its own effect depending on the purpose.

Figure 2 shows an example of a circuit inserted into the receiver video amplification circuit and its characteristics as a trap for a 10KHz offset beat within the same channel. This circuit configuration causes distortion and is not suitable for incorporating into an IC receiver.

(Summary of the Invention) An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to solve the problem of interference waves mixed in the same channel, especially interference waves mixed in both sideband regions of a television signal wave using the vestigial sideband amplitude modulation method. This design effectively eliminates the effects of interference by minimizing the loss of the desired wave, making it suitable for IC integration in combination with a SAW filter (surface acoustic wave device), and receiving interference wave removal configuration with almost no phase distortion. The aim is to provide the equipment.

That is, the receiving device of the present invention is a receiving device for receiving an amplitude modulated vestigial sideband television transmission signal. The narrowband filter group includes at least two even-numbered narrowband filters that vertically symmetrically divide upper and lower sidebands of both sideband portions included in the television transmission signal; The delay time of each narrowband filter in the filter group is almost equal, and the insertion loss of the center frequency of each narrowband filter is approximately equal to the delay time of each narrowband filter.
Each of the narrowband filters successively contacts each other at a frequency where the loss increases by 6 dB, and the insertion loss at the center frequency is approximately equal, and further a circuit is provided for controlling and combining the outputs from each of the narrowband filters at an appropriate level. It is characterized by being prepared.

(Example) Broadcasting using vestigial sideband amplitude modulation method
The frequency band of the NTSC television signal is
As shown in Figure 3, it is a 6MHz video carrier wave.
f _V , color subcarrier f _C , and audio carrier f _A are multiplexed, and the bands are classified into 1 to 5.

1 and 2 are frequency bands in which the low frequency parts of the luminance signal and the synchronization signal are transmitted in both bands, and are the most important bands in the television signal. 3
4 is the high frequency portion of the luminance signal, a portion where the color signal is multiplexed with both side bands, and 5 is the audio region.

As stated in the (Summary of the Invention) section, the gist of the present invention is to configure the IF filter of a television signal receiving device with three or more narrowband filters having adjacent frequency band passbands, and A filter group (also called a filter bank) consists of narrowband filters that can independently receive the upper and lower sideband portions that are transmitted on both sides of the television transmission band, and is a filter dedicated to audio carrier waves. Apart from the case where the insertion loss is included, the characteristics are set to be adjacent at the frequency where the loss increases by about 6 dB from the minimum insertion loss of the narrowband filters (the frequency where the amplitude is halved), and the output from each narrowband filter is It was designed to be synthesized at an appropriate level.

An example of a method for configuring a group of narrowband filters is shown in FIG. 5a. Two narrowband filters are placed adjacent to each other at the frequency of the video carrier wave _fV , and six narrowband filters are arranged with the center frequency of each narrowband filter approximately 1MHz apart, with a 6dB bandwidth of approximately 1MHz. .

Under normal reception conditions, the insertion loss of the narrowband filter for frequency bands 1 and 2, which are transmitted with both sidebands, is 6 dB larger than the insertion loss of the narrowband filters 3 and 4, and is at the level indicated by the dotted line in the figure. It is combined with the outputs of 3 and 4 narrow band filters and detected. At this time, the outputs of the 5 filters for the audio carrier wave are added at appropriate levels or processed separately.

If interference is mixed in one or two bands, and it is in either frequency band, the output of the relevant narrowband filter is reduced to zero or the output is reduced until the interference is negligible, and then Adjust the insertion loss of one narrowband filter to be the same as the narrowband output filters 3 and 4, or adjust the voltage sum of the output of that filter and the output of the side whose output has been reduced to be the same as before. In other words, one output is subtracted, the other output is increased by the amount, and the signals are added and detected. In this way, the video signal can be demodulated as a completely normal video signal.

If the interfering radio wave falls within the frequency band 3-1 or 3-2, the output of the corresponding narrowband filter is reduced to a level where the interfering signal beat can be ignored and added. In this case, although the resolution of the video signal is degraded, the received image quality is improved compared to when no corresponding measures are taken and beat interference exists.

If the interference radio wave falls within the frequency band 4, the corresponding narrow band filter output is reduced to a level where the interference signal beat can be ignored and added. In this case, the color signal will be removed, and in extreme cases the video signal will become a monochrome signal, but the received image quality will be better than if beat interference were present.

FIG. 5b shows another example of a filter bank configuration. In this case, only the double sideband wave portions can be received by independent filters, and the single sideband portion is received by one filter. It is clear from the above description that even if an interfering radio wave is mixed into either side band wave, the interfering radio wave is completely removed.

Figure 5c shows a case in which the IF filter is further configured with a group of narrowband filters, with two narrowband filters in contact with each other on the video carrier wave, and the center frequencies of each narrowband filter separated by approximately 0.51MHz. This is a case where 10 pieces are arranged, and one more piece is arranged for the audio carrier wave, for a total of 11 pieces. If the jamming signal is 1-1,1
-2, 2-1, or 2-2, the output of the narrowband filter is set to zero, and the sideband waves (1-1 and 2-2) that are in the relationship between the narrowband filter and the upper and lower sidebands are 2 or relationship between 1-2 and 2-1)
The output of the narrow band filter is doubled when there is no interference and then added for detection, or the same method as taken in 1 and 2 of Fig. 5a is used. As a result, it can be demodulated as a completely normal video signal. Interfering signal from 3-1 to 3
-4, the narrow band filter output is reduced to a level where interference can be ignored and added. When the signal enters either band 4-1 or 4-2, the output of the other narrowband filter is doubled and added for detection. In this case, color shift occurs, but it can be demodulated as a color signal.

It should be noted here that the filter bank described above can currently be realized using surface acoustic wave filter technology, and a narrowband filter group without phase distortion suitable for IC technology can be provided.

FIG. 6 shows an embodiment in which the above-mentioned IF filter bank 1 is incorporated into a television receiver.
The television signal received by the antenna 3 is channel selected 4, frequency converted 5, and introduced into the IF filter bank 1 described above. On the other hand, the interference signal in the video signal is detected by the beat frequency detection circuit 14.
detects the beat frequency, and depending on which frequency band of the filter bank the beat frequency falls into,
A control circuit 7 of the filter bank generates a control signal to control the level adjustment synthesizer 2. As a result, a video signal without beat interference is obtained as a detection output, and the R, G, and B color signals are then reproduced in the usual manner to display a television image. The audio carrier is also sent to the frequency discriminator 16 in the usual manner.

FIG. 7 shows another embodiment of the present invention in which the first half of the above-mentioned television receiver is used as part of a television relay transmitter. Even if there is beat interference in the input signal, the television signal from which the beat interference has been removed is retransmitted.

(Effects) As described in the section explaining the embodiments, the effects of the present invention are that interference waves mixed in television signals transmitted using the vestigial sideband amplitude modulation method can be effectively suppressed by suppressing the loss of desired waves as much as possible. It consists in removing.
The most basic method is to configure the filter filter of the IF filter of the receiving device with three narrowband filters as shown in Figure 5b, but as the band of jamming radio waves becomes narrower, the number of filter filters in the IF filter of the receiving device is made up of three narrowband filters. It is advisable to use the scheme shown in Figure 5c. Furthermore, the above-mentioned filter bank can be easily realized using surface acoustic wave filter technology.Surface acoustic wave filters are characterized by no phase distortion, unlike filters with L and C configurations, and are also suitable for integration technology. Since it is suitable, the effectiveness of the present invention is greatly increased by using the above-mentioned surface acoustic wave filter technology.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining a conventional diversity reception method aimed at removing interference waves, Fig. 2 is a diagram showing a conventional trap example and its characteristics for a 10KHz offset beat within the same channel, and Fig. 3
The figure shows the arrangement of in-channel frequencies in television NTSC vestigial sideband AM transmission, Figure 4 is a diagram for explaining the basic configuration of the present invention, and Figure 5 shows the IF narrowband filter group (filter) of the present invention. FIGS. 6 and 7 are block diagrams respectively showing a television signal receiving and displaying device and a relay transmitting device incorporating the present invention. 1... IF filter bank, 2... Level adjustment synthesizer, 3... Receiving antenna, 4... Channel selector, 5... Frequency converter, 6... Local oscillator, 7... Control circuit, 8... Detection circuit, 9... Video amplifier, 10... Luminance color signal separation, 11... Color signal regeneration circuit, 12... Television image display, 13... Synchronization separation circuit, 14... Beat frequency detection circuit, 15 ...Audio IF filter, 16...
...Frequency discriminator, 17...Audio amplifier, 18...
Speaker, 19...Modulator, 20...Local oscillator, 21...Power amplifier, 22...Transmission antenna.

Claims (1)

[Claims for Utility Model Registration] 1. In a receiving device that receives an amplitude modulated vestigial sideband television transmission signal, at least three frequency filters each having a desired passband of the receiving device and having passbands whose frequencies are adjacent to each other are provided. The narrowband filter group includes at least two even-numbered narrowband filters that vertically symmetrically divide the upper and lower sidebands of the both sideband portions included in the television transmission signal, and The delay time of each narrowband filter of the narrowband filter group is approximately equal, and the narrowband filters are adjacent to each other in sequence at a frequency where the insertion loss is increased by approximately 6 dB from the insertion loss of the center frequency of each narrowband filter, A television signal receiving apparatus characterized in that the center frequency insertion loss is approximately equal, and further comprises a circuit for controlling and combining outputs from each of the narrowband filters at an appropriate level. 2 Utility Model Registration Scope of Claims 1. In the receiving device according to claim 1, a disturbing beat frequency is detected from the television transmission signal, and an output signal from the narrowband filter containing the disturbing frequency that causes the disturbing beat frequency is detected. 1. A television signal receiving apparatus comprising: a control synthesis circuit that attenuates the beat interference until it becomes inconspicuous and adjusts the total frequency output characteristics of the television transmission signal. 3. In the receiving device according to claim 2 of the utility model registration, when no interfering radio waves are included in the frequency corresponding to the narrowband filter of the double-side band portion, the narrow-band filter of the double-side band portion When the output from the narrowband filter is approximately 1/2 of the output from the other narrowband filters, and when interfering radio waves are mixed either above or below the double-side band section, the insertion loss of the corresponding narrowband filter is set to 1/2 of the output from the other narrowband filters. Increase the beat interference caused by radio waves until it becomes inconspicuous,
By adjusting the insertion loss of the narrowband filter in which the upper and lower sides of the sideband form a pair with the narrowband filter, the voltage sum of the output signals of the frequencies in which the upper and lower sides of the sideband form a pair is approximately 1/2 the level of the above output. 1. A television signal receiving device comprising: the control synthesis circuit capable of synthesizing the signal so that the signal is approximately equal to that obtained when the signals are added together.