JPS58114585A - Television signal transmitter and receiver - Google Patents

Abstract

PURPOSE:To secure excellent transmission quality with limited sending power by using a high frequency signal at the top end of a video signal band or outside of said band as a horizontal synchronizing signal, and maximizing the frequency shift of a video signal within a permissible range. CONSTITUTION:A frequency demodulating circuit 31 demodulates a TV signal 20 and a band-pass filter 32 extracts a high frequency signal 21 containing the horizontal synchronizing signal from the demodulated signal. An envelope detection circuit 33 detects the envelopes of the output signal of the filter 32 to extract a horizontal synchronizing frequency component. A synchronizing pulse and gate signal generating circuit 34 generate various gate signals and horizontal synchronizing pulses. A synchronizing pulse inserting and clamping circuit 35 replaces the horizontal synchronizing signal part in the demodulated signal passed through a delay device 36 from the demodulating circuit 31 by the horizontal synchronizing pulses from the circuit 34 on the basis of the gate signals of the circuit 34 to perform DC regeneration. The resulting signal provides a television composite signal similar to the signal for a normal TV receiver.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an apparatus for transmitting and receiving frequency modulation television signals used, for example, in satellite broadcasting systems.

Technical Background of the Invention Generally, in the transmission and broadcasting of television signals on SHFHF, and in particular in satellite broadcasting, a frequency modulation method is adopted to ensure good transmission quality even with low transmission power. VSB-AM as modulation signal
The television broadcasting signal (see Figure 1 for the waveform), which is similar to that in television broadcasting based on the -! Well, it's often used.

Problems with the Background Art However, in the above television composite signal, since the horizontal synchronizing pulse 1 occupies about 30% of the effective amplitude, the video signal 2
If the maximum frequency deviation is kept constant, the signal-to-noise ratio will deteriorate by the amount of the horizontal synchronization pulse l. Therefore, in order to ensure excellent transmission quality within the given frequency bandwidth and transmission power constraints, it is desirable to expand the amplitude of the video signal 2 to the horizontal synchronizing pulse l portion.

OBJECTS OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a frequency modulation type television signal transmitting/receiving device that can improve the signal-to-noise ratio.

Summary of the Invention In other words, the present invention uses a high frequency signal at the end of the video signal band or outside the above band as a horizontal synchronization signal, thereby keeping the frequency deviation of the video signal at its maximum within a permissible range. .

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a waveform fIl of a television composite signal that is a modulation signal of a frequency modulation type television signal transmitted by the apparatus of the present invention.

20 is a video signal, and within the horizontal retrace period 6), for example, a high frequency around 4 MHz (this is near the end of the video signal band, but it may be a higher frequency than this band). The signal 21 is multiplexed as a horizontal synchronizing signal, and a color burst signal 22 is inserted a little later. These high frequency signals 21 and color burst signals 22
・The video signal 20 is inserted into the level section whose level is shifted between the white level and the black level. Therefore, in the television signal frequency-modulated by the television composite signal, the maximum frequency deviation of the video signal is the maximum (100%) within the allowable frequency bandwidth.

On the other hand, FIG. 3 shows a television signal receiving apparatus as described above, in which 3 is a frequency demodulation circuit for demodulating the television signal input, and 32 is a frequency demodulation circuit for demodulating the input television signal, and 32 is an output signal from the demodulation circuit 3. 33 is an envelope detection circuit for extracting the horizontal synchronization frequency component by envelope detection of the output signal of the F wave generator 32; 34; is this detection circuit 33
synchronization A? to generate various necessary dart signals and horizontal sync pulses based on the output signal of A? Based on the dirt signal from this circuit 34, a pulse and dart signal generation circuit 35 converts the horizontal synchronization signal portion of the demodulated signal led from the demodulation circuit 31 through the delay device 36 into a horizontal synchronization signal generator from the circuit 34. This is a synchronous pulse insertion and clamp circuit for replacing the DC current and regenerating the DC current. Note that the delay device 36 is for delaying the demodulated signal by an amount corresponding to the signal delay in the path from the band F wave generator 32 to the synchronization pulse insertion and clamp circuit 35.

In the receiving device having the above configuration, the output a of the demodulation circuit 3, the output b of the band wave transducer 32, and the envelope detection circuit 33
01 synchronous pulse and f-) synchronous pulse output d of the signal generation circuit 34 and e-) signal output e1 synchronous pulse 4 insertion pulse and output f of the clamp circuit 35, respectively, as shown in FIG. Finally, the same television composite signal as in a normal television receiver is obtained. Therefore, this composite signal output is connected to the video detection system for analysis similar to that in a normal television receiver.
Can be renewed. The communication method between the above-mentioned television signal transmitting and receiving devices is a frequency modulation method, in which a synchronization signal using a high frequency signal is used instead of a synchronization pulse so that the video signal can be transmitted up to 100% of the allowable frequency deviation. Since it is inserted superimposed on the Bedemetal level, the signal-to-noise ratio of the video detection output is approximately 3 d lower than before.
B.Improving.

The frequency of the high-frequency signal used as the horizontal synchronization signal is an integral multiple of twice the horizontal synchronization frequency, or the relationship between the color subcarrier frequency and the integer ratio, for example, NTSC.
In the method (15,73426kHz x 2)
If you use 2X7X13KT (5727 kT (z), which has a lower frequency than the video signal band), the phases of all the synchronization signals and the rising parts of the synchronization pulse will be in phase, making it possible to maintain more stable synchronization. The first point is that it can be done.
FIG. 5 shows an example of a configuration for making the most of these points. That is, the modulated output of the demodulation circuit 31 is guided to the synchronous detection circuit 51, where the horizontal synchronization signal (high frequency signal) included in the demodulated output is synchronously detected and the frequency, phase, rise time and length of this high frequency signal are determined. information such as duration (signal width). This information is then led to the synchronization pulse and dart signal generation circuit 52, which counts and steps down the surface frequency signal frequency to generate synchronization pulses and dart signals in the correct time relationship, and then sends them to the synchronization pulse insertion and clamp circuit 35. Output.

Note that the present invention is not limited to the above embodiments, but
Even if other signals such as frequency spread signals or color subcarrier frequency signals outside the video band modulated with data, audio, etc. are superimposed on the television composite signal shown in the figure, the features of the present invention will not be lost.

゛It goes without saying that the high-frequency signal as the horizontal synchronization signal does not have to be a perfect sine wave, and may also have a waveform containing other information.
The present invention is not limited to the embodiment shown in Figure 5, but the point is to detect a high frequency signal component as a horizontal synchronizing signal from the frequency demodulation circuit output, and use this detection output to reproduce a normal television composite signal. The circuit can be configured arbitrarily. - Effects of the Invention As described above, according to the television signal transmitting/receiving device of the present invention, when a frequency modulation method is adopted to ensure good transmission quality with limited transmission power, the frequency shift of the video signal is reduced. Since it is possible to maintain the maximum signal-to-noise ratio within the allowable occupied bandwidth, it is possible to obtain the highest quality signal-to-noise ratio within a limited frequency band.Moreover, the frequency of the high-frequency signal for the horizontal synchronization signal can be kept at a predetermined value on the transmitting side. By setting this to , you can ensure stable synchronization on the receiving side.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the waveform of a waste video signal of a conventional television transmission signal, and FIG. 2 to FIG.
Fig. 2 is a waveform example of a composite video signal of a transmission signal, Fig. 3 is a block diagram showing an example of a receiving device, Fig. 4 is a waveform diagram for explaining the operation cost of Fig. This is a modification of the figure. 20... Video signal, 21... High frequency signal (horizontal synchronization signal), 3... Frequency demodulation circuit, 32... Band F
wave detector, 33...Envelope detection circuit 1.34...Sync pulse and dirt signal generation circuit, 35...Sync pulse insertion and clamp circuit. Applicant's Representative Patent Attorney Takehiko E 10- Figure 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) A high frequency signal near the high end of the video signal band or outside this band is superimposed as a horizontal synchronization signal during the horizontal retrace period of the television video signal to produce a television composite video signal, and this composite video signal is used as a transmission signal. a television transmitter equipped with means for keeping the maximum frequency deviation of a video signal to the maximum within the allowable occupied bandwidth when frequency modulating the video signal; A means for detecting a high frequency signal corresponding to a synchronizing signal to generate a horizontal synchronizing pulse, inserting this horizontal synchronizing pulse into a composite video signal in place of the horizontal synchronizing signal such as the high frequency signal, and then performing video detection. (iF
A television signal transmitting and receiving device comprising a television receiving device and a television receiving device. (2) In the television transmitting device, the high frequency signal is set to a frequency that is an integral multiple of twice the horizontal synchronization frequency.
The television signal transmitting/receiving device described in Section 1. (3) The television signal transmitting/receiving device according to claim 1, wherein in the television transmitting device, the high frequency signal is set in a relationship of an integer ratio with a color subcarrier frequency. Device.