JPS581868B2 - Bidirectional data transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bidirectional data transmission device in a unidirectional public listening system.

In general, bidirectional CATV systems use a single cable and perform bidirectional transmission by frequency division into upstream and downstream directions.When transmitting data in a CATV system, these systems are used to transmit data in both directions using a polling method. Data is being transmitted towards the destination.

However, in these bidirectional systems, expensive bidirectional line amplifiers are used in the transmission line, so the cost of the transmission line equipment is currently extremely high.

Moreover, if you want to perform bidirectional data transmission in a conventional unidirectional system, you cannot reuse these conventional unidirectional devices, and instead use a bidirectional system using expensive bidirectional line amplifiers. must be introduced.

In view of the above points, the present invention makes bidirectional data transmission possible by adding an adapter including a simple filter and diode switch to the conventional unidirectional public listening system.

More specifically, the downstream data signal uses a downstream data carrier within the frequency band of the communal amplifier, as in the past.
Transmission is performed by modulating the carrier wave with the data signal, but the upstream data signal is transmitted by baseband pulse transmission, making it possible to transmit the upstream data signal as used in conventional bidirectional systems. The present invention is designed to easily and inexpensively perform bidirectional data transmission in a unidirectional public listening system using a dendritic distribution network without using a modulator/demodulator for transmission.

Hereinafter, the present invention will be explained based on illustrated embodiments.

In FIG. 1, 1 is a VHF antenna, 2 is a UHF antenna, 3 is a modulator for downlink data signals, and 4 is a line receiver for uplink data signals.

Also, 5 and 6 are mixers, 7 is a common amplifier for the downstream direction,
Denoted at 8, 13, 16, and 22 are branching filters that separate uplink signals and downlink signals, each consisting of a low-pass filter and a high-pass filter.

9 is a distributor, and 10 is a distribution output line of the distributor 9.

11, 12, 18.19 are turnouts including adapters, 2
0 is a terminating resistor, and 27 is a branch output line from the branch 12.

17 is a line amplifier, 14 is a conventional communal amplifier similar to 7 above, 15 is a regenerator for uplink data signals, 21 is a terminal device, 23 is a line driver for sending out uplink data signals, 2
4 is a demodulator for downlink data signals, 25 is a distributor for distributing downlink signals, and 26 is a terminal for outputting a television signal, which is an output terminal of the distributor 25.

Figure 2 shows the turnout 11 (or 12, 18, 19) in Figure 1.
) is a circuit diagram showing a specific example of the configuration.

In the same figure 2, 30.31 are input/output terminals, 32, 3
3.46, 47.48.49 are 8 (or 13 in Figure 1)
, 16.22) and similar duplexers, 35, 36. 38, 3
9.40 is the bias fixing resistor, 41, 42, 43, 4
4.45 is a diode, 34 is a conventional public listening splitter, 5
0a, 50b, 50c, and 50d are conventional public listening splitters 34
Down signal branch output lines from 51a, 51b, 51c,
51d is a branch output terminal.

Moreover, FIG. 3 is a circuit diagram showing a specific example of the configuration of the line amplifier 17 in FIG. 57 is a line driver for transmitting upstream data signals of baseband pulses, 58 is a line receiver for upstream data signals, and 59 and 60 are terminating resistors.

Next, the operation of the embodiment of the present invention will be explained with reference to FIGS. 1, 2, and 3.

First, in FIG. 1, a television signal and a downstream data signal mixed by a mixer 6 are amplified to a predetermined level by a communal amplifier 7, passed through a high-pass filter in a splitter 8, and distributed by a distributor 9. .

The down signal from the distribution output line 10 enters the branch 11,
After a portion of the signal is split, it enters the next splitter 12.

Thereafter, the signals are branched at branchers 18 and 19 in the same manner.

In addition, the downlink signal whose level has attenuated on the way is transmitted to the line amplifier 1.
7 to a predetermined level.

The downlink signal that entered the turnout 12 from the turnout 11, that is, the second
In the figure, the downlink signal input from the input/output terminal 30 is branched by a conventional public listening splitter 34, passes through the respective splitters 46, 47, 48, and 49, and is passed through the branch output terminals 51a, 5.
1b, 51c, and 51d as branch outputs.

In this way, the downlink signal outputted from the branch output line 27 in FIG. Output.

The other distributed output enters the downlink data signal demodulator 24, is demodulated, and then taken out as a downlink data signal.

Then, by sequentially scanning the terminals using this downlink data signal, data is collected from the corresponding terminal using the uplink data signal.

In this way, the polling method causes the corresponding terminal to send out an uplink data signal of baseband pulses using the uplink data signal sending line driver 23 in the terminal device 21.

Note that in terminals that do not correspond, no pulse signal is sent from the output of the line driver 23 for sending up data signals, so the pulse signal is always at a constant DC level.

For example, if the output of the line driver 23 is at TTL level, it is at low level.

This upstream data signal is sent out through a low-pass filter within the duplexer 22.

However, it is assumed that the cutoff frequency of the low-pass filter is at the minimum necessary frequency position at which the waveform of the pulse signal after passing through the filter does not cause any trouble in transmission.

The baseband pulse uplink data signal that has passed through the splitter 22 enters the splitter 12 from the branch output line 27 .

That is, in FIG. 2, the upstream data signal of the baseband pulse input from the branch output terminal 51a is sent to the branching filter 46 again.
The signal is separated from the downstream signal and enters a diode 41 connected in the forward direction to a low-pass filter in the duplexer.

This diode 41 becomes conductive when the baseband pulse is output, and the baseband pulse passes through the diode 41.

The upstream data signal of the baseband pulse that has passed through the diode 41 is reversely connected to the diodes 42, 43, 44, and 45 because no upstream data signal is applied to the other branch terminals 51b, 51c, and 51d. The signal is then cut off, and is not output to the other branch terminals 51b, 51c, 51d or the input/output terminal 31, but is sent to the input/output terminal 30 through the low-pass filter in the duplexer 32.

Also, bias fixing resistors 35, 36, 37, 38, 39
．． It is assumed that 40 has a resistance value sufficiently large compared to the line impedance, and signal transmission loss due to these can be ignored.

Also, these are diodes 41, 42, 43, 44.4
5 and the branching filters 32, 33, 51a, 51b connected to
If the outputs of 51c and 51d are disconnected for some reason, the disconnected terminals will become electrically floating.
This is to prevent other diodes, which should normally be non-conductive, from becoming conductive and the upstream data signal flowing into them, thereby preventing an increase in signal transmission loss.

In addition, since the diode has a very high resistance value when reverse biased, the conductive diode 41 is connected in parallel with the other non-conductive diode 42.
,43,44.45 can be ignored,
Equivalently, the branching filter 4 connected to the branch output end 51a
6 and the duplexer 32 connected to the input/output terminal 30, only the diode 41 is connected in series.

The uplink data signal of the paceband pulse inputted from the branch output line 27 as described above is inputted from the branching device 12 to the next branching device 11 and then inputted to the distribution output line 10.

The divider 9 also has the same configuration as the splitter 12 (not shown), so that the upstream data signal input from the distribution output line 10 passes through the duplexer 8 and enters the line receiver for upstream data signals.

As described above, the line driver 23 of the terminal device 21
The baseband pulse uplink data signal sent out from the baseband pulse is always transmitted in the direction of the line receiver 4 by the diode in the splitter and divider, and by the line receiver 4,
It is extracted as an uplink data signal.

In addition, if a line amplifier 17 is inserted in the middle of the line to compensate for the decrease in signal level, the downstream signal is amplified by the communal amplifier 14 and sent out, and the upstream data signal of the baseband pulse is The waveform is shaped by the regenerator 15 and sent out.

That is, in FIG. 3, the downstream signal input from the input/output terminal 52 passes through a high-pass filter in the duplexer 55, is amplified by the communal amplifier 54, and is sent through the duplexer 56 again to the input/output terminal 53. .

On the other hand, the baseband pulse upstream data signal input from the input/output terminal 53 is separated from the downstream signal by a low-pass filter in the duplexer 56 and input to the line receiver 58 .

Typically, line receivers have high input impedance, so
Impedance matching is performed by the termination resistor 60.

The upstream data signal whose waveform has been shaped by the line receiver 58 is sent out again to the transmission path by the line driver 57.

As described above, since the present invention transmits uplink data signals by baseband pulse transmission, uplink data transmission is performed by modulating the uplink data carrier wave with the uplink data signal as in the conventional method. Compared to the conventional method, a modulator and demodulator for uplink data signal transmission are not required.

Moreover, all conventional unidirectional devices can be used, and bidirectional data transmission can be easily performed by simply adding a simple adapter to them.

In addition, by providing directional switches using diodes in branchers and distributors, distribution in them can be improved.
The loss required for the splitter can be reduced, and data transmission in the upstream direction can be performed using baseband pulses even in a distribution network such as a public listening system using ordinary line drivers and line receivers. This is something that can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of the present invention, and FIGS. 2 and 3 are circuit diagrams showing a specific example of the structure of the main part of the embodiment. 1...VHF antenna, 2...UHF
Antenna, 3... Downlink data signal modulator, 4
, 58... line receiver for uplink data signals,
7,14.54・・・Community amplifier, 8,13,1
6, 22, 32, 33, 46, 47, 48, 49, 55
．． 56...brancher, 9, 25...divider, 11, 12, 18.19...brancher, 23
, 57...Line driver for transmitting uplink data signals, 24...Demodulator for downlink data signals, 34
・・・・・・Community listening switch, 35, 36, 37, 38,
39.40...Bias fixing resistor, 41,4
2, 43, 44, 45,... Diode.

Claims (1)

[Claims] 1. A unidirectional public listening branch and divider in a CATV line whose input terminals and output terminals include a low-pass filter and a high-pass filter for separating upstream and downstream signals on the line. Set up a wave device,
The high-pass filter is connected to the input/output terminals of the branching device and the distributor, and the low-pass filter in the branching means is provided with a directional switch means made of a diode, and the branching output terminal and the distribution output of the branching device and the distributor are connected to each other. For the duplexer connected to the terminal, the anode terminal of the diode is connected to the low-pass filter, and a bias fixing resistor is provided as a bias fixing means for fixing the bias to the anode terminal of the diode. The cathode terminals of the diodes are all connected in common to form a common terminal, and the common terminal is connected to a low-pass filter of a duplexer provided at the input terminal of the duplexer and divider. At the same time, by connecting a bias fixing resistor, an adapter comprising a means for transmitting data in the upstream direction is added to the unidirectional public listening branch and divider.
1. A bidirectional data transmission device, characterized in that data is transmitted in the upstream direction using a baseband pulse transmission method in a dendritic line network.