JPH02162911A - Amplifier for catv - Google Patents

Abstract

PURPOSE:To use the amplifier regardless of the specifications of the CATV system by providing a level adjustment device varying the level of a pilot signal. CONSTITUTION:When an input signal is outputted from a main amplifier 1, a SAW surface acoustic wave filter 2 of an AGC circuit 9 extracts only a pilot signal from an output signal. The attenuation of a variable attenuator 6 is adjusted by using amplifiers 3, 5 and a detector 4 in response to fluctuation of the level of the pilot signal to be extracted so as to make the gain adjustment in a way that the output of the main amplifier 1 is always constant. A level adjustment device 7 is formed by providing a -6dB attenuator 7a in parallel with part (part not including other components) of the AGC circuit 9 and then providing a +6dB amplifier 7b. Thus, the input level is kept or 6dB amplification is selected by switching the switch against the input of the pilot signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [& Field of Application of Tojo] The present invention relates to a CATV amplifier device for compensating for transmission loss in a CATV system.

[Prior Art] In a CATV system, an amplifier as shown in FIG. 5 is provided on the main line F in order to compensate for the transmission loss of the television signal on the main line and maintain a predetermined signal level.

This type of amplifier device includes a main amplifier l, a variable attenuator 6,
It includes a preamplifier 8 and an automatic gain control circuit (hereinafter abbreviated as AGC circuit) 9.

A predetermined signal level is obtained by transmitting a pilot signal from the headend device together with the television signal, and adjusting the gain in the amplifier according to the level of the pilot signal.

That is, the AGC circuit 9 of the amplifier device extracts only the pilot signal from the output of the main amplifier l using the SAW filter (surface acoustic wave filter) 2, and extracts only the pilot signal from the output of the main amplifier l. Detector 4.
The attenuation degree of the variable attenuator 6 is adjusted by the amplifier 5. As a result, automatic gain control is performed, and the output level of the main amplifier l is always -constant.

Now, as a gain control method in the conventional CATv system, first, as shown in Fig. 6, pilot signals for each wave are set on both high and low sides of the frequency range of the television signal.
There is a method in which the higher wave is used as a reference for gain control, and the level difference between the higher and lower waves is used as a reference for slope adjustment. However, in this method, noise is generated due to intermodulation of the pilot signals of the two high and low liquids. In order to deal with the occurrence of such noise, the influence of noise has been reduced by lowering the level of the pilot signal by, for example, 6 dB than the level of the television signal.

However, such a method is not used much at present.

The general control methods currently in use are 1. A.S.
There is a method of using a C (automatic slope control) circuit to place a pilot signal only on one side of the frequency range of the television signal, as shown in FIG. 7, and controlling the gain based on this. Therefore, according to this method, the phase of the pilot signal of two high and low liquids! There is no noise generation due to f modulation, and there is no need to lower the level of the pilot signal.

[Problem to be solved by the invention 1 As mentioned above, in the current CATV system,
There is no need to lower the pilot signal level, but in order to maintain compatibility with the predecessor's CATV system, the pilot signal level must be lowered by 6 dBIi than the television signal level, as before.

In reality, the above measures differ depending on the CATV system manufacturer, and CATV systems with different pilot signal reference levels coexist, causing confusion.

[L stage for solving the problems] The present invention solves the above-mentioned conventional problems and provides a CATV amplifier head that can be used regardless of the specifications of the CATV system.

In order to achieve such an object, the present invention provides a main amplifier for amplifying a television signal transmitted on a main line, a variable attenuator for adjusting the main amplifier gain, and a television signal from the output side of the main amplifier. and an automatic gain control circuit that branches a pilot signal transmitted together with the pilot signal and adjusts the degree of attenuation of the variable attenuator using the pilot signal as a reference.
In the ATV amplifier, the automatic gain control circuit includes:
It is characterized by being provided with a level adjuster that changes the level of the pilot signal.

[Embodiment 1] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a CATV amplifier according to an embodiment of the present invention, and FIG. 2 is a diagram showing an embodiment of a level adjuster according to the present embodiment.

The CATV amplifier device of this embodiment includes a main amplifier l and a preamplifier 8 for amplifying the television signal transmitted on the main line, and a variable attenuator 6 for adjusting the gain of the main amplifier l, An AGC circuit 9 is provided which branches a pilot signal transmitted together with the television signal from the output side of the main amplifier 1 and adjusts the attenuation degree of the II range attenuator 6 based on the output of the pilot signal.

In this embodiment, a television signal and a pilot signal are mixed through a main line from a headend device (not shown) and are manually input from the preamplifier 8 side.

When the above human input signal is output from the main amplifier l, the AGC
The SAW filter 2 of the circuit 9 extracts only the pilot signal from the output signal. The attenuation degree of the Iif variable attenuator 6 is adjusted by the amplifiers 3 and 5 and the detector 4 according to fluctuations in the level of the extracted pilot signal, thereby adjusting the gain so that the output of the main amplifier l is always constant. .

Here, the level adjuster 7 adjusts the level of the pilot signal in a width of 6 dB. As a result, the AGC circuit 9 can operate normally even if the CATV system has specifications that lower the pilot signal level or matches the pilot signal level to the television signal. becomes. Although the level adjuster 7 is provided between the amplifier 3 and the detector 4 in this embodiment,
No matter where in the AGC circuit 9 it is placed, there is no functional difference.

Next, level tone! An embodiment of the luger 7 will be explained with reference to FIGS. 2 to 4.

The level adjuster 7 shown in FIG. 2 is a part of the AGC circuit 9 (
-6 dB for the part that does not include other elements).

Attenuator 7a of +6 dB is installed in parallel, followed by +6 dB amplifier 7b.
It has been established. Therefore, by changing the switch, it is possible to select whether to maintain the input level or to amplify the pilot signal by 6 dBp.

Next, the other side of the level adjuster is shown in FIGS. 3 and 4. FIGS. 3 and 4 are diagrams showing other examples of the level adjuster of this embodiment, respectively. The level adjuster 7 shown in FIG.
This is the same as the 6 dBIL amplifier 7c. Second
It works similarly to the one shown. If the level adjuster 7 is configured as shown in FIG. 3, the number of parts will be small and the cost will be low.

The level adjuster 7 shown in FIG. 4 includes a +6 dBuL amplifier 7d provided in a part of the AGC circuit 9, and further includes ii) a variable attenuator 7e. By using the IIf variable attenuator 7e, the level of the pilot signal can be continuously varied in a width of 5an. Therefore, by finely adjusting the attenuation degree, an accurate attenuation degree of 1F can be obtained.

Note that even if the level adjuster 7 shown in this embodiment is not used, it may be used for the amplifier 3 or 5. ') A similar effect can be obtained by providing an adjustment function.

1 shot 1 effect] As explained above, the CATV amplifier device of the present invention has the effect of
By providing a level adjuster in the GC circuit, it can be used in CATV systems with different pilot signal reference levels, so it can be used when equipment from other manufacturers with different specifications is mixed in the same ATV system, or C
Even when equipment with different specifications is introduced when expanding or partially replacing an ATV system, it can be handled.

In addition, since the level adjuster works in the same way no matter where it is installed in the AGC circuit, it is possible to install only the level adjuster or its changeover switch (or volume) outside of the CATV amplifier to facilitate the switching operation. be able to.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a CATV amplifier according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the level adjuster in FIG. 1, and FIGS. FIG. 5 is a circuit diagram showing another embodiment of the level adjuster in FIG. 1, FIG. 5 is a circuit diagram showing a conventional CATV river amplifier, and FIG. 6 is a diagram showing a pilot signal of a conventional CATV system. FIG. 7 is a chart showing pilot signals of current CATV systems. 1: Main amplifier 2: SAW filter (surface acoustic wave filter) 3.5 = amplifier 4: Detector

Claims (1)

[Claims] A main amplifier for amplifying a television signal transmitted on a main line, a variable attenuator for adjusting the main amplifier gain,
An automatic gain control circuit that branches a pilot signal transmitted together with a television signal from the output side of the main amplifier and adjusts the degree of attenuation of the variable attenuator using the pilot signal as a reference, the CATV amplifier device comprising: CAT characterized in that the automatic gain control circuit is provided with a level adjuster that changes the level of the pilot signal.
V amplifier.