JPS6242553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modulation conversion system for television broadcast signals, which is used for relaying television broadcast signals between a television broadcast station and a relay television broadcast station.

Depending on the installation conditions of the relay TV broadcast station, direct relay using TV broadcast waves becomes impossible, and it is necessary to install a relay station in between, and in such cases, an amplitude modulated signal is used. The video signal is converted into a frequency modulated video signal (hereinafter referred to as FM).
In addition to V), it has become suitable for use in street relays.

That is, generally, a television broadcast signal consists of an amplitude modulated video signal (hereinafter referred to as AM-V) in which a carrier wave is amplitude-modulated by a video signal, and a frequency-modulated audio signal in which a subcarrier having a predetermined frequency interval with this carrier wave is frequency-modulated by an audio signal. signal (hereinafter referred to as FM-
A) However, in order to avoid the influence of noise having an amplitude component during relay transmission, it is desirable to transmit all signals as frequency modulated signals, and for this purpose, AM-
TV broadcast signal consisting of V and FM-A,
It is necessary to perform modulation conversion to a television composite signal consisting of FM-V and FM-A.

FIG. 1 is a block diagram showing a _conventional example of a modulation conversion method used in such a case.
A television broadcast signal consisting of carrier wave _c and FM-A, which is frequency-modulated by audio signal A on subcarrier _sc having a predetermined frequency interval of 4.5 MHz, is demodulated by an intercarrier demodulator ICDM. A composite signal consisting of the video signal V and FM-A with the frequency spectrum shown in the baseband shown in Figure 3 is made, and is separated into the video signal V and FM-A centered on the subcarrier _sc by a demultiplexer FD. After the FM-A is demodulated by the frequency detector FMDT into the original signal with the frequency spectrum shown in Figure 4, the second subcarrier _sc2 , which is generally 7.5MHz, is frequency-modulated by the frequency modulator FMMD ₁ and then re-modulated. Since FM-A, video signal V
The second carrier wave _sc2 corresponding to the relay transmission frequency is synthesized by the synthesizer MIX, and the second carrier wave sc2 is sent to the frequency modulator.
Frequency modulation is performed again using FMMD ₂ , and the frequency spectrum FM-V and FM shown in Figure 5 are
- A TV composite signal consisting of A was obtained from the output OUT.

That is, this causes the second carrier wave _c2 and the second carrier wave c2 to
The frequency interval with subcarrier _sc2 is 7.5MHz,
The signal-to-noise ratio at the receiving point is improved, but as mentioned above, the repeating of demodulation and modulation makes the circuit configuration complex, and the transmission characteristics of each circuit affect the signal obtained from the output OUT, which increases manufacturing costs. In addition, it has the drawback of being undesirable from the viewpoint of deterioration of signal fidelity.

The present invention aims to fundamentally eliminate such drawbacks of the conventional art, and directly frequency modulates a predetermined carrier wave using the output of an intercarrier demodulator, and
This provides a modulation conversion method with an extremely simple configuration that modulates a relay input television broadcast signal consisting of FM-V and FM-A into a relay output television composite signal consisting of FM-V and FM-A. be.

The details of the present invention will be explained below with reference to the block diagram of FIG. 6 showing an embodiment.

In the same figure, the value of Figure 2 given to the input IN is
The television broadcast signal consisting of AM-V and FM-A is processed into the baseband video signal V and FM as shown in Fig. 3 in the intercarrier demodulator ICDM.
-A, thereby resulting in a predetermined carrier wave _ct having a frequency corresponding to the transmission frequency.
is frequency-modulated by a frequency modulator FMMD, and a television composite signal consisting of FM-V and FM-A whose frequency spectrum is shown in FIG. 7 is obtained from the output OUT.

However, as in the case of Figure 1, the audio signal is FM
- Since the frequency is further modulated by A, it becomes double frequency modulated. In addition, since frequency modulation is performed directly by the output of the intercarrier demodulator ICDM, the frequency interval of 4.5 MHz between carrier wave _c and subcarrier _sc shown in Figure 2 is reproduced as is in Figure 7, and the predetermined carrier wave _ct and subcarrier _s
The frequency interval with _c is the same as in Figure 1, and is 4.5MHz.
A frequency interval of is obtained.

Note that the frequency interval between both carrier waves _ct and _sc is the fifth
Since it decreases to 4.5MHz compared to 7.5MHz in the figure,
Although the degree of improvement in the signal-to-noise ratio at the reception point is slightly reduced, if the transmission power and the conditions of the relay section are taken into consideration, results equivalent to the conventional method can be obtained.As shown in Figure 6, the circuit configuration is extremely simplified. It can be manufactured at low cost, and signal fidelity deterioration is reduced, which is extremely advantageous.

As is clear from the above explanation, according to the present invention, the frequency interval between the carrier wave and the subcarrier wave in the television broadcast signal is used as is to perform modulation conversion, so the circuit configuration is simplified, resulting in low cost and high fidelity. It is possible to achieve modulation conversion of the same frequency, and there is no need to particularly change the configuration of the relay television broadcasting station, and it can be applied to street relay repeaters, etc., and has great effects.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example, Figs. 2 to 5 show the frequency spectrum of each signal in each part of Fig. 1, Fig. 2 shows an input television broadcast signal, and Fig. 3 shows an intercarrier signal. FIG. 4 shows the original audio signal at the output of the frequency detector; FIG. 5 shows the output TV composite signal; FIG. 6 is a block diagram showing an embodiment of the invention;
FIG. 7 is the frequency spectrum of the television composite signal at the output of FIG. IN...Input, ICDM...Intercarrier demodulator,
FMMD...frequency modulator, _ct ...predetermined carrier wave,
OUT…Output.

Claims (1)

[Claims] 1 Consisting of a video signal and a frequency modulated audio signal whose baseband is a relay input television broadcast signal consisting of an amplitude modulated video signal and a frequency modulated audio signal using a subcarrier having a predetermined frequency interval from the carrier wave of the video signal It consists of an intercarrier demodulator that demodulates into a composite signal, and a frequency modulator that modulates the frequency of a predetermined carrier wave using the output of the intercarrier demodulator, and the frequency interval between the predetermined carrier wave and the subcarrier wave is adjusted to the predetermined frequency interval. A modulation conversion method characterized in that a television composite signal consisting of a frequency modulated video signal and a frequency modulated audio signal whose frequency interval is the same as that of the frequency modulator is obtained as a relay output from the output of the frequency modulator.