JPH0637676A - Frequency characteristic measuring method for transmission line in community antenna television system - Google Patents

Abstract

PURPOSE:To attain the measurement of the frequency characteristic of a transmission line over the entire transmission band by transmitting a measuring signal to the transmission line for a CATV system and using a white noise as the measuring signal. CONSTITUTION:A measuring signal source 7 generating the white noise is mouted on the side of the head end 5 of a main line 1. Besides, a spectrum analyzer for measuring the white noise 10 is mounted in the middle of the main line 1. The head end 5 broadcasts in the frequency band of the frequency 73 to 451.25MHz. The measuring signal source 7 is composed of a noise generator 8 and an amplifier 9 so as to generate the white noize of the frequency 73 to 451.25MHz by the noise generator 8 and to simultaneously amplify it into a level which can be measured by the spectrum analyzer 10 by the amplifier 9 to output it to the main line 1. Thus, the white noise of a uniform level is used as the measuring signal without regard to the frequency so that the frequency characeristic of the transmission line can be measured over the entire frequency band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the frequency characteristic of a transmission line such as a trunk line in a CATV system, which has an abnormality in an amplifier in the transmission line, a connection failure of a connector, a change in ambient temperature, etc. It is suitable for measuring the level change of the transmission signal generated by.

[0002]

2. Description of the Related Art A transmission line in a CATV system is an important part connecting a center and subscribers, and a trunk line is particularly important. For this reason, the frequency characteristics of the transmission line are measured at the time of installation or after installation. Normally, such measurement is performed from the center A to the TV as shown in FIG.
At the same time as the signal, both upper and lower ends of the transmission band (usually 73M
Hz and 451.25 MHz) and transmit the pilot signal to the trunk line B, which is transmitted in the middle of the trunk line B (for example, the amplifier C).
Monitor terminal) and monitor it with a measuring device D such as a spectrum analyzer.

[0003]

However, in the measurement method using the pilot signal in the forefront, only the level of the pilot signal at both ends of the transmission band can be measured. Therefore, it is necessary to confirm the signal level of the frequency between the pilot signals. I can't. Therefore, for example, in the case where a notch phenomenon E occurs, as shown in FIG. 5, in which only a signal having a frequency in the middle is interrupted due to a connection failure in a connector attached to a coaxial cable or an amplifier in the middle of the trunk line. I couldn't confirm it.

An object of the present invention is to provide a method capable of measuring the frequency characteristic of a transmission line over the entire transmission band.

[0005]

A method of measuring frequency characteristics of a transmission line in a CATV system according to the present invention includes transmitting a measurement signal to a transmission line 1 of the CATV system and extracting the measurement signal as shown in FIG. In the frequency characteristic measuring method of the transmission line in the CATV system for measuring the frequency characteristic of the transmission line 1, white noise is used as the measurement signal.

[0006]

In the method of measuring the frequency characteristic of the transmission line in the CATV system of the present invention, white noise having a uniform level is transmitted to the transmission line 1 regardless of the frequency as shown in FIG. 2, and the change in the level of this noise is measured. The frequency characteristic of the transmission line 1 can be easily measured by measuring with the instrument 10. For example, if the connector on the transmission line 1 has a contact failure, as shown in FIG.
And 451.25 MHz), the notch N generated in the frequency band without 45 MHZ can also be observed.

[0007]

1 shows an embodiment of a method for measuring frequency characteristics of a transmission line in a CATV system of the present invention.
Is a transmission line (main line) connecting the headend 5 and the subscriber, 6
Is a main amplifier installed in the main line 1. A measurement signal source 7 for generating white noise is attached to the head end 5 side of the main line 1, and a spectrum analyzer 10 for measuring the white noise is attached in the middle of the main line 1. The head end 5 is broadcasting in the frequency band of 73 to 451.25 MHz.

The measuring signal source 7 is composed of a noise generator 8 and an amplifier 9.
White noise of 3 to 451.25 MHz (indicated by a dotted line in FIG. 2) is generated, and is amplified to a level (indicated by a solid line in FIG. 2) that can be measured by the spectrum analyzer 10 by the amplifier 9 to the main line 1. It can be output.

[0009]

According to the frequency characteristic measuring method of the transmission line in the CATV system of the present invention, since the white noise whose level is uniform regardless of the frequency is used as the measurement signal, the transmission line 1 of the transmission line 1 is distributed over the entire frequency band. The frequency characteristic can be measured.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a method of measuring frequency characteristics of a transmission line in a CATV system of the present invention.

FIG. 2 is an explanatory diagram showing an example of white noise output from a measurement signal source in the measurement method of FIG.

3 is an explanatory diagram showing an example of white noise observed by a spectrum analyzer in the measuring method of FIG.

FIG. 4 is a schematic diagram showing a conventional method of measuring a transmission line using a pilot signal.

5 is an explanatory diagram showing a state of a signal measured by the pilot signal of FIG.

[Explanation of symbols]

 1 transmission line

Claims (1)

[Claims] 1. A method for measuring a frequency characteristic of a transmission line in a CATV system for transmitting a measurement signal to a transmission line of the CATV system, extracting the measurement signal, and measuring the frequency characteristic of the transmission line. A method for measuring frequency characteristics of a transmission line in a CATV system, characterized in that white noise is used as a signal.