JPH05130578A - Frequency-multiplex signal transmission system - Google Patents

Abstract

PURPOSE:To enable long-distance transmission and use a coaxial cable of optional length without inserting an equalizing circuit nor an amplifier halfway into the coaxial cable. CONSTITUTION:A sent signal is equalized by the equalizing circuit 1. Further, when a transmission distance is short, the signal is attenuated by an ATT 3, but when the transmission distance is long, the signal is equalized again by the equalizing circuit 4 and sent through the coaxial cable 6; and a reception device 70 amplifies the received signal by an AGC amplifier 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for transmitting frequency-multiplexed signals.

[0002]

2. Description of the Related Art Conventionally, CATV (cable television) has been mentioned as a method of transmitting a frequency-multiplexed signal using a coaxial cable.

As another frequency-multiplexed signal transmission device, a device without a circuit (equalization circuit) for correcting the cable length of a coaxial cable at the time of transmission is sold.

[0004]

[Problems to be Solved by the Invention] However, C
In a method of transmitting a frequency-multiplexed signal over a long distance like ATV, a circuit (equalization circuit) for correcting frequency characteristics per length of a coaxial cable which is a transmission cable
Since the amplifier circuits are arranged at constant distances, it is impossible to select the coaxial cable at any distance.

Further, in a transmission device having no equalization circuit, there is a drawback that long-distance transmission cannot be performed because the transmission distance can be transmitted only tens of meters due to the attenuation of the frequency multiplexed signal by the coaxial cable.

[0006]

The present invention has been made in order to solve the above problems, and the present system has the following configuration. That is, in a device that performs frequency-division multiplex transmission, either the transmission device or the reception device has an equalization circuit and its switching means for each fixed distance, and the reception device reduces the attenuation of the transmission coaxial cable. By having an AGC amplifier or an amplifier for correction, it becomes possible to select a coaxial cable of any length when transmitting a frequency-multiplexed signal, and further, in the middle of the coaxial cable that is the transmission path, etc. It is possible to freely perform transmission from short distance to long distance without inserting a conversion circuit and an amplifier.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the frequency multiplex transmission system in this embodiment.

FIG. 2 is a level diagram showing the level of each point in FIG. 1 (coaxial 5D-2W).
LOSS-20 dB / 100 m (500 MHz)).

In FIG. 1, the coaxial cable 5D
A block diagram for the case of using -2W with a length of 0 to 200 m is shown.

To the input point A of the transmitter 10, frequency multiplexed signals of the same level are input as shown in FIG. 2A. The input signal is equalized by the equalization circuit 1 into the frequency characteristic shown in FIG. 2B. The equalized signal is switched by the switch 3, and the attenuator (ATT 10d
B) It is inputted to either 3 or the equalization circuit 4. When input to ATT3, the coaxial cable 6 is 0
˜100 m, and the case where the coaxial cable 6 is input to the equalization circuit 4 is 100 to 200 m.

When the coaxial cable 6 is 0 to 100 m, B
The signal at the point is attenuated by 10 dB at ATT3, and becomes the level shown in FIG. 2C. The signal at the point C is connected to the coaxial connector 5 through the changeover switch 2. Then, the coaxial connector 5 and the coaxial connector 7 are connected by the coaxial cable 6, and the frequency-multiplexed signal is transmitted from the transmitter 10 to the receiver 70. Then, the transmitted frequency multiplexed signal is input to the AGC (automatic gain control) amplifier 8. At this time, since the attenuation amount of the signal at the frequency differs depending on the length of the coaxial cable 6, FIG.
The level is as shown in 1. In addition, in FIG. 2E-1, the case where the coaxial cable 6 is 0 m, 50 m, and 100 m is shown. Therefore, depending on the length of the coaxial cable 6, the signal level moves in the range of 0 m to 100 m shown in FIG. 2E-1.

The coaxial cable 6 has a length of 100 to 200 m.
In the case of, the signal at point B is the changeover switch 2
Is input to the equalization circuit 4. The equalization circuit 4 equalizes the signal levels shown in FIG. 2D. After equalization, the frequency-multiplexed signal takes the same course as described above and is input to the AGC amplifier 8. At this time, the level of the signal input to the AGC amplifier 8 is as shown in FIG. 2E-2. Figure 2
E-2 shows the case of the coaxial cable 6 of 100 m, 150 m, and 200 m. Therefore, when the coaxial cable 6 has a length of 100 m to 200 m, the signal level moves in the range of 100 to 200 m shown in FIG. 2E-2 according to the length.

When the coaxial cable is 0 to 100 m or 100 to 200 m, the AGC amplifier 8 similarly amplifies the signal levels shown in FIGS. 2E-1 and E-2. At this time, since the amplification degree is changed by the AGC amplifier 8,
As shown in FIG. 2F, the output of the AGC amplifier is 100 to 200 m when it is 0 to 100 m.

By switching the equalizing circuit 4 according to a certain transmission distance and amplifying the received signal by the AGC amplifier 8 of the receiver in this way, even when the length of the coaxial cable is long, the time when the coaxial cable is short is used. Signals can be transmitted with the same characteristics.

At this time, at the point E, there may be a slight level difference between the high frequency and the low frequency depending on the length of the coaxial cable. However, the entire configuration including this transmission method causes this level difference. It does not matter if it is allowed.

Although the ATT 3 and the equalizing circuit 4 are switched in the embodiment shown in FIG. 1, the number of equalizing circuits can be increased to extend the transmission distance. Further, by shortening the switching distance of the equalization circuit 4, it is possible to reduce the level difference between the low frequency and the high frequency. Further, the equalization circuit may be brought to the receiving device side.

Furthermore, it is also effective to divide the equalization circuit into both transmitting and receiving devices and transmit a frequency-multiplexed signal.

The AGC amplifier may be composed of ordinary amplifiers.

An amplifier may be provided before or after the equalization circuit and before and after the equalization circuit to amplify the frequency-multiplexed signal.

[0021]

As described above, in the device for transmitting the frequency-division multiplexed signal, the transmitting device or the receiving device has an equalizing circuit for each constant distance and its switching means.
In addition, the receiving device has an AGC amplifier or an amplifier that corrects the attenuation of the transmission coaxial cable, so that when transmitting a frequency-multiplexed signal, the equalization circuit and the amplifier are provided in the middle of the coaxial cable that is the transmission path. Long-distance transmission is possible without inserting a cable, and short-distance to long-distance transmission can be freely performed. Further, there is an effect that it is possible to select any length of the coaxial cable.

[Brief description of drawings]

FIG. 1 is a block diagram showing a method of transmitting a frequency-multiplexed signal according to an embodiment of the present invention.

FIG. 2 is a level diagram showing changes in signal level of each part of the block of FIG.

[Explanation of symbols]

 1 Equalization circuit 2 Changeover switch 3 10 dB ATT 4 Equalization circuit 5, 7 Coaxial connector 6 Coaxial cable 8 AGC amplifier

Claims (1)

[Claims] 1. A transmitting device or a receiving device for transmitting a frequency-multiplexed signal has an equalizing circuit for each transmission distance and its switching means, and the receiving device has an automatic gain control amplifier or an amplifier. And frequency multiplexing signal transmission system.