JPH0413887Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of a system for multiplex transmission of television camera signals through a single coaxial cable.

[Conventional technology]

Conventionally, in television camera systems, main video signals, audio signals, data signals such as microcontrollers, and power are transmitted between the camera head and the base station that controls it using a triaxial cable. There are things that can be done in one go. In this case, a system is adopted in which each signal has a different carrier frequency and is frequency multiplexed and transmitted. In this case, in order to make the cable length between the camera head and the base station as long as possible, it is advantageous to have a lower carrier frequency, and the main video and the like are arranged in a lower frequency band. Figure 2 shows the frequency arrangement of the transmission signal. Frequencies are assigned from the direct current component (DC) to 103MHz.

Here, the main video 26MHz modulator 1 is
As shown in the figure, this is a reactance FM modulator using a varactor 2, and its output is frequency-multiplexed by a filter 3 along with the outputs of other modulators 4 and 4' with different frequencies, and transmitted via a coaxial cable 6. .

In this case, it is important to have a high S/N ratio, especially for the main video signal, in order to transmit the S/N of the camera head without degrading it, and for that purpose, it is necessary to increase the degree of modulation and increase the degree of S/N improvement. There is.

Therefore, conventionally, the modulation depth of 26MHz modulator 1 is set in a region where transmission system distortion does not occur.
Due to the low frequency band, the modulation degree cannot be set sufficiently large, and as a result, the S/N ratio is just one step away.

[Problem that the invention attempts to solve]

As described above, in the conventional technology, the carrier frequency is set low for long-distance transmission of main video, and as a result, it is difficult to ensure sufficient linearity of the modulator and it is difficult to obtain a sufficient S/N. do not have.

In order to solve these drawbacks, the present invention aims to enable long-distance transmission of mainline video with a sufficient S/N ratio even in a low frequency band without impairing the linearity of the modulator.

[Means for solving problems]

In order to achieve the above purpose, this invention modulates the high frequency, then converts it to the original low frequency using a local oscillator and mixer, multiplexes it with other waves using a filter, and transmits it. It is.

[Effect]

As a result, since modulation at a high frequency requires a narrow fractional band, a large degree of modulation can be ensured and a large S/N ratio can be achieved.

〔Example〕

An embodiment of this invention will be described below with reference to FIG. The main video modulator consists of a high frequency 140MHz modulator 7 modulated by a varactor 2. This output is frequency-converted with the output of the local oscillator 8 of 114MHz by the mixer 9 to obtain a modulated wave of 26MHz. After amplifying this with 26MHz amplifier 2, filter 3
The output signal is combined with the outputs of other harmonics 4 and 4', and frequency-multiplexed transmission is performed via the coaxial cable 6.

The modulator 7 described above modulates at a high frequency of 140MHz, so a large modulation depth is possible.
Since the degree of S/N improvement can be increased, the S/N can be increased without causing deterioration of linearity in the modulator.

In this case, the modulation frequency and local oscillation frequency of the modulator 7 must be selected so that spurious signals do not fall into other carrier frequencies.

[Effect of idea]

According to the present invention, by using frequency conversion, the S/N ratio can be improved without impairing the linearity of the modulator, and a high-performance television camera signal multiplex transmission device is possible. Become.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing the frequency arrangement of the present device, and FIG. 3 is a block diagram showing a conventional example. 4, 4', 7...Modulator, 3...Filter, 2,
5, 5'...Amplifier, 8...Local oscillator, 9...
Mixer, 6...Coaxial cable.

Claims (1)

[Scope of utility model registration request] Video signals, audio signals, and
In a television camera signal multiplexing transmission device that frequency multiplexes transmission of various signals such as control signals, the video signal is modulated by a modulator with a modulation frequency higher than the carrier frequency band of the coaxial cable, and the signal is transmitted by frequency conversion means. A television camera signal multiplex transmission device characterized in that the television camera signal multiplex transmission device is configured to convert the frequency to a lower frequency within the carrier frequency band, frequency multiplex it with other modulated waves, and transmit the signal.