JPS60171884A - Signal transmission system of two-way catv system - Google Patents

Abstract

PURPOSE:To eliminate a wave interferring an incoming signal by using a frequency band of an idle channel in an outgoing transmission band, converting the incoming signal to a frequency of a trunk line system and connecting the signal to the trunk line system. CONSTITUTION:The incoming signal of a frequency band of n-channel being an idle channel of the frequency band of the outgoing signal is transmitted to a distribution tap (i) from a subscriber (j), the incoming signal enters a frequency converter (c) via a directional coupler (g), an incoming branch amplifier (h) and a band pass filter (e), the incoming signal is converted into the frequency band of the existing incoming signal in 10MHz-50MHz by the frequency converter (c) and then inputted to an incoming trunk line amplifier (l).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal transmission method for a two-way CATV system, and is designed to reduce external interference waves that intrude into upstream signals from subscriber systems.

In conventional two-way CATV systems, the transmission frequency band is 10MHz to 50MHz for the 11X signal transmitted from the subscriber to the center, and the transmission frequency band for the downlink signal transmitted from the center to the subscriber. 70MHz-250MHz or 300MHz is used.

However, in the frequency band of IOM) (about 50 MHz), it is not uncommon for air waves, especially short wave bands, to enter the cable as interference waves.

In the current system, even if countermeasures against interference are taken for the trunk line, distribution system, and other facilities outside the home, the in-home wiring, receivers,
Since interference waves enter the transmitter and their connections, the influence of interference waves on upstream signals cannot be eliminated unless countermeasures are taken against them.

However, it is very difficult to individually implement countermeasures against interference waves at each subscriber's premises, and it causes a great deal of inconvenience to the subscribers.

In addition, when converting a unidirectional transmission line into a bidirectional one, most of the equipment, except for the cable, must be replaced with one that has bidirectional functionality, resulting in large-scale construction work and huge costs. There is also.

Therefore, the present invention makes it possible to remove interference waves from upstream signals without making any changes to the existing equipment of the CATV system.

Therefore, in the present invention, an empty channel in the frequency band of the downlink signal, which is less susceptible to interference waves, is used as the frequency band of the uplink signal in a place where it is difficult to take countermeasures against interference waves, such as in a subscriber's company premises. This is to reduce the influence of interference waves.

The present invention will be explained in detail below based on the drawings.

FIG. 1 is a block diagram of a two-way CATV system incorporating the method of the present invention. At No. 11N, the downlink signal sent from the main line A is sent to the branching filter m of the main line branch amplifier B, the down line branch amplifier d, and the notch filter f.
, via a directional coupler g to a distribution tap i, from where it is distributed to each subscriber j.

On the other hand, from subscriber j to distribution tap i, an upstream signal using an n-channel frequency band, which is an empty channel in the downstream signal frequency band, is transmitted, and this upstream signal is sent to a directional coupler g and an l branch amplifier. h.

The -E signal is inputted to a frequency converter C via a band pass filter e, and the -E signal is inputted to a frequency of 10M by this frequency converter C.
) Iz to 50 MHz (7) It is converted to the current -L signal frequency band and then input to the upstream trunk amplifier l.

Note that the 7-2 filter f and the bandpass filter e in FIG. 1 are for increasing the isolation between the upstream signal and the downstream signal.

The one shown in Figure 1 is a bidirectional CATV transmission system that is equipped with a downlink trunk amplifier and an uplink trunk amplifier l, while the one shown in Figure 2 is a two-way CATV transmission system that converts the existing unidirectional CATV transmission system into a bidirectional one. FIG. 1 is a block diagram of a two-way CATV system incorporating the signal transmission method of the invention.

This is done by inserting a duplexer 2 on the input/output side of the amplifier l in order to convert the unidirectional trunk branch amplifier l into a dual-channel amplifier l.
An uplink dedicated amplifier 3 with a transmission band of IOMH2 to 50MH2 is inserted between the OW outputs to make the main line bidirectional.

In the case of Fig. 2, as in the case of Fig. 1, the uplink signal from the subscriber is transmitted using the 70MH frequency band, which is the transmission frequency band of the downlink signal.
z-250MI (z or 300MH2) is used for transmission, and this upstream signal is input to the directional coupler 4 connected to the branch terminal of the unidirectional trunk branch amplifier l for downlink only, and the signal from the 4 terminals is The signals are mixed by a mixer 5, the mixed upstream signal is amplified by an amplifier 6, and it is inputted to a converter 8 through a bandpass filter 7 and connected to the main line -
The frequency of the signal is converted to the L-band transmission band, and the signal is coupled to the trunk uplink dedicated amplifier 3 through the directional coupler 9.

As described above, the present invention uses the frequency band of an empty channel within the downlink transmission band, which is less susceptible to interference from air waves, as a one-time signal from subscriber j, and transmits this uplink signal to the uplink transmission band of the trunk system. Since the frequency is converted to the frequency of

(1) Since there is almost no interference from airwaves from the subscriber's in-house wiring, branch lines, or distribution trunk lines, upstream signals will hardly be interfered with by airwaves if sufficient countermeasures are taken for the trunk lines. do not have.

(2) Bidirectional transmission is possible by using the existing in-house wiring, branching, and distribution systems without any modification, and by adding bidirectional devices only to the main line, making it possible to put it into practical use. It is easy and economical.

(3) Since the trunk line uses conventional frequency bands for both E and downlinks, uplink signals from subscribers can be transmitted to the center using conventional bidirectional trunk amplifiers. Moreover, it is easy to put into practical use and is also economical.

[Brief explanation of the drawing]

FIGS. 1 and 2 are various explanatory diagrams of signal transmission methods of a bidirectional CATV system according to the present invention. l is a downlink-only unidirectional main line branch amplifier 2 is a branching filter 3 is a reverse main line amplifier 4.9 is a directional coupler A is a main line B is a main line branch amplifier C is a converter g is a directional coupler m is a duplexer The downlink mains amplifier l is 1; the downlink mains amplifier

Claims (2)

[Claims] (1) In a two-way CATV system, the frequency band of an empty channel within the downlink transmission band is used as the uplink signal from the subscriber's home, and this uplink signal is frequency-converted to the frequency of the downlink transmission band of the trunk system. A signal transmission system for a two-way CATV system, characterized in that the cable is connected to a main line system. (2) The two-way CATV according to claim 1, characterized in that the upstream signal from the subscriber's home is frequency-converted to the frequency of the tri-transmission band of the trunk system in the trunk branch amplifier. System signal transmission method.