JPH0575210B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency conversion device for a two-way CATV system used to transmit information between terminal devices using the two-way CATV system.

(Prior art) Conventionally, in the case of centralized monitoring systems that transmit security information such as fire and theft using transmission lines of bidirectional CATV systems, and systems that aggregate and process meter reading information for water, gas, etc. In order to be able to connect a terminal device that functions as a central device to the location of the terminal device, a frequency conversion device provided on the head end side converts the upstream frequency signal from the terminal device into a downstream frequency signal.

In other words, the terminal device has the function of modulating the upstream frequency signal with transmission information and transmitting it, and the function of demodulating only the downlink frequency signal and receiving the transmission information. A method is adopted in which the frequency converter converts the signal into a downlink frequency signal and transmits the signal to another terminal device for reception.

Therefore, in a transmission system that uses frequency conversion to distinguish upstream and downstream frequency signals, the frequency conversion device installed at the head end plays an extremely important position in the operation of the system. However, during long-term use,
The frequency converter may malfunction, and if there is an abnormality in the frequency converter, it will no longer be able to convert to a downlink frequency that can be received by the terminal device, resulting in loss of transmission function between terminals, and the frequency converter may fail. The reliability of the system was directly linked to the reliability of the system.

In order to solve this problem, it is conceivable to adopt a backup method in which two frequency converters are provided in the frequency converter, and when one breaks down, it is switched to the normal one.

(Problem to be Solved by the Invention) By the way, in the case of a backup system in which two frequency converters are provided, for example, the output level of a mixer in the frequency converter is monitored, and if the output level falls below a predetermined value, Sometimes it is determined that there is an abnormality and the user switches to another frequency converter. However, regarding the transmission of security information such as fire and theft,
It uses the CAMA (Carrier Sense Multiple Access) method, in which the terminal device sends a signal on the condition that there is no carrier on the transmission line when an abnormality such as fire or theft is detected, so the frequency conversion device Since the upstream frequency signal is not constantly supplied to the mixer, simply monitoring the output level of the mixer may incorrectly determine that there is an abnormality in the frequency conversion device when no signal is being sent from the terminal device. There was a problem in which the frequency converter switched even though it was normal.

(Means for Solving the Problems) The present invention has been made in view of such conventional problems, and it reliably prevents erroneous abnormality judgments in a state where no signal is sent from the terminal device. ,
The frequency of the two-way CATV system is designed to reliably determine whether or not the converted signal level is normal when a signal is sent from the terminal, and to switch back up in the event of an abnormality, greatly increasing the reliability of the frequency converter. The purpose is to provide a conversion device.

In order to achieve this objective, the present invention provides a main frequency converter and an auxiliary frequency converter, and monitors the level difference between the mixer input level (first input level detection) and output level in the main frequency converter. When this level difference is outside of a predetermined value, it is determined to be abnormal (first level determination), and further, the mixer input level of the main frequency converter (first input level detection) and the auxiliary frequency converter are determined as abnormal. The level difference between the mixer input levels (second input level detection) is compared, and even when this level difference is outside a predetermined value, it is determined to be abnormal (second level determination), and one of these is determined to be abnormal. When the frequency converter is obtained, switching control is performed from the main frequency converter to the auxiliary frequency converter.

(Embodiment) FIG. 2 is a system diagram of a bidirectional CATV system in which the frequency conversion device of the present invention is used.

First, the configuration will be described. Reference numeral 1 denotes a head end. From the head end 1, a CATV line 2 is led out toward a terminal, and bidirectional amplifiers 3 are installed along the way of the CATV line 2 at every predetermined line length.

4 is a terminal device, which is connected to the branch terminal of the branch 5 provided on the CATV line 2, the branch terminal of the branch 5 provided on the branch line of the bidirectional amplifier, or the branch terminal of the bidirectional amplifier 5, etc. There is. This terminal device 4 has a function of mutually transmitting information with other terminal devices via the CATV line 2.

That is, when the terminal device 4 detects a fire, gas leak, etc., it modulates the upstream frequency signal f2 with a signal code containing this abnormality detection information and sends it to the CATV line 2. In addition to the detection information, the code signal that modulates the upstream frequency signal f2 includes address information of a destination terminal and a block check code. On the other hand, the reception function of the terminal device 4 is to receive a downlink frequency signal f having a frequency different from the uplink frequency f2.
1, and the downlink frequency signal f1
It determines its own call by demodulating it, and when it determines its own call, it decodes the information signal sent along with the address information and performs alarm processing, etc.

Here, the uplink frequency f2 transmitted from the terminal device 4
For example, a frequency band of 10 MHz to 50 MHz is used, and an unused frequency band of 70 MHz or more is used as the downlink frequency f1.

Furthermore, any one terminal device among the plurality of terminal devices 4 can be given the function of a center device, and necessary information can be transmitted by polling other terminal devices from the terminal device having the function of the center device. The information transmitted by this polink is applied to, for example, meter reading data of electricity, water, etc. with low urgency, while information with high urgency such as fire, theft, etc. is transmitted by the terminal device itself. Transmission processing using the CSMA method is adopted, which creates a request and sends it out on the condition that there is no carrier on the transmission line.

In order to enable transmission between terminals that have the function of modulating such an upstream frequency signal f2 with an information signal and demodulating only the downstream frequency signal f1, a branch is made to the CATV line 2 on the head end 1 side. A frequency conversion device 7 of the present invention is connected through the device 6 . The frequency conversion device 7 has a function of receiving the uplink frequency signal f2 sent from the terminal device 4, frequency modulating it into a downlink frequency signal f1, and sending it out again to the CATV line 2.

FIG. 1 is a block diagram showing an embodiment of the frequency conversion device of the present invention.

First, the configuration will be described. Two frequency converters, a main frequency converter 10 and an auxiliary frequency converter 20, are provided. Main and auxiliary frequency converter 10, 20
is connected to CATV on the head end side via distributor 8.
connected to the line.

Taking the main frequency converter 10 as an example, the configuration of the frequency converter includes a bandpass filter 12 that extracts the upstream frequency signal f2 from the output of the coupler 11;
A low amplifier amplifies the upstream frequency signal f2, a PLL local oscillator 14 whose oscillation frequency can be adjusted by externally setting the frequency division ratio, and an upstream frequency signal f by mixing the output of the low amplifier 13 and the local oscillation output.
a mixer 15 for converting 2 into a downlink frequency signal f1;
A high amplifier 16 that amplifies the frequency-converted downlink frequency signal f1, and a bandpass filter 17 that extracts only the downlink frequency signal f1 and supplies it to the coupler 11.
Equipped with.

The basic configuration of such a frequency converter is the same for the auxiliary frequency converter 20, and the coupler 2
1, band pass filter 22, low amplifier 23,
It includes a PLL local oscillator 24, a mixer 25, a high amplifier 26, and a bandpass filter 27.

Furthermore, in the present invention, in order to determine an abnormality in the frequency converter, regarding the main frequency converter 10,
An input level detector (first input level detector) 18 is provided between the low amplifier 13 and the mixer 15 to detect the input level of the up frequency signal f2, and
An output level detector 19 is provided between the high amplifier 16 and the bandpass filter 17 to detect the output level of the frequency-converted down frequency signal f1. On the other hand, regarding the auxiliary frequency converter 20, the upstream frequency signal f is also connected between the low amplifier 22 and the mixer 25.
An input level detector (second input level detector) 28 is provided to detect the second input level.

If a switching method is adopted in which when an abnormality in the main frequency converter 10 is detected, the operation is switched to the auxiliary frequency converter 20 by switching the power supply, the operation of the auxiliary frequency converter 20 is performed while the main frequency converter 10 is in operation. In this case, power is supplied only to the low amplifier 23 and the input level detector 28, which are the pre-circuit sections, and when the power source is switched, power is supplied to other circuit sections.

Next, the means for determining an abnormality in the frequency converter based on the detection outputs of the input level detectors 18, 28 and the output level detector 19 and switching to the auxiliary side is as follows.

First, the detection output E1 of the input level detector 18 in the main frequency converter 10 and the output level detector 19
The detection output E3 is given to the level difference detection means 30, and the input/output level difference ΔE1 is detected. In addition, the input level detector 1 in the main frequency converter 10
The detection output E1 of 8 and the detection output E2 of the input level detector 28 in the auxiliary frequency converter 20 are given to the level difference detection means 32, and the input level difference ΔE2 between the two frequency converters is detected. .

Input/output level difference △E1 of level difference detection means 30
is given to the comparison means 34, and it is determined whether or not it is within a predetermined value indicated by the reference voltage source 36. If a level difference ΔE1 exceeding the predetermined value occurs, the comparison means 34 outputs an H signal indicating an abnormality in the frequency converter. Produces level output. In addition, the input level difference between the two frequency converters by the level difference detection means 32 is also given to the comparison means 38 and compared with a predetermined value indicated by the reference voltage source 40. When the level difference ΔE2 exceeds the predetermined value, the frequency Produces a high level output indicating converter abnormality.

Therefore, the level detecting means 30 and the comparing means 34, which determine the input/output level difference of the main frequency converter 10, constitute a first level determining means, and the second level determining means
The level difference detection means 32 and the comparison means 38, which determine the input level difference between the two frequency converters, constitute a second level determination means.

The output of comparison means 34 and 38 is data /O42
is given to the CPU 44 via the RO
It is equipped with an M/RAM 46 and a display 48, etc., and when an H level output of at least one of the comparison means 34 or 38 is obtained, an abnormality of the frequency converter is displayed on the display 48, and at the same time, the data/O
A switching control signal for switching the operation of the frequency converter 10 in which the abnormality has occurred to the operation of the auxiliary frequency converter 20 is outputted via the terminal 42 .

Because of this switching to the auxiliary side, the data/O4
2, the power supply control means 50 and the local control means 5
2 is provided.

When switching to the auxiliary side by the power supply control means 50, as described above, the main frequency converter 10
In the operating state, the auxiliary frequency converter 20 supplies power only to the low amplifier 23 and the input level detector 28, and the power supply to other circuit sections is stopped. Therefore, when a switching control signal to the auxiliary side is obtained from the CPU 44 via the data/O 42, the power supply control means 50 cuts off the power supply to the main frequency converter 10, and
Power is supplied to circuit sections other than the front circuit in the auxiliary frequency converter 20.

Furthermore, switching to the auxiliary side is also possible by local oscillator control of the PLL local oscillators 14 and 24 by the local oscillator control means 52. That is, the main frequency converter 10
In the operating state, the PLL local oscillator 24 of the auxiliary frequency converter 20 is inactive, thereby stopping the frequency conversion function of the auxiliary frequency converter 20. Switching to the auxiliary side is performed by the main frequency converter 10
At the same time as stopping the operation of the PLL local oscillator 14 of
The PLL local oscillator 14 of the auxiliary frequency converter 20 is activated.

Next, the operation of the embodiment shown in FIG. 11 will be explained. still,
For switching to the auxiliary side, use the power supply switching method as an example.

First, if the frequency converter 10 is normal, the upstream frequency signal f2 sent from the terminal device is transmitted to the distributor 8.
is applied to the coupler 11 from the output of the coupler 11, and the upstream frequency signal f2 is passed through the bandpass filter 12.
is taken out and amplified by low amplifier 13, and mixer 1
5, the frequency is converted into a downlink signal f1 by mixing it with the local oscillation output of the PLL local oscillator 14. The frequency-converted downlink frequency signal f1 is amplified by a high amplifier 16, and then passed through a bandpass filter 17.
After removing unnecessary components, the signal is sent out to the CATV line via the coupler 11 and the distributor 8.

At this time, the detection output E1 of the input level detector 18
The detected output E3 of the output level detector 19 is either equal in level or the difference in level is within a certain range, and the output of the comparing means 34 is set at the L level. In addition, in the auxiliary frequency converter 20, since power is supplied only to the low amplifier 23 and the input level detector 28, the main frequency converter 10
Similarly, the input level E2 of the upstream frequency signal f2 is detected, and the level difference ΔE2 determined by the level difference detection means 32 is zero or within a certain range, and the comparison means 38 also produces a level output.

Next, in a no-signal state where the upstream frequency signal f2 is not sent from the terminal device, the input level detector 1
8, 28 and the output level detector 19 are at approximately zero level, and the level differences △E1, △E2 are also zero or within a certain range, so the outputs of the comparing means 34, 38 are both at L level. becomes. That is, even if the upstream frequency signal f2 is not being sent from the terminal device, an error in the frequency conversion device will not be detected incorrectly.

Next, when a failure occurs in the front side of the mixer 15 in the frequency conversion device 10, that is, in the bandpass filter 12 or the low amplifier 13, the detection output E1 of the input level detector 18 decreases. At this time, since the pre-circuit on the side of the auxiliary frequency converter 20 is normal, the output E2 of the input level detector 28 is normal, and the level difference ΔE detected by the level difference detection means 32 is normal.
2 increases and exceeds the predetermined value, and the comparison means 38 indicates H.
By generating a level output, the CPU 44 instructs the power supply control means 50 to switch the power supply, cuts off the power supply to the main frequency converter 10, and supplies power to all the circuit parts of the auxiliary frequency converter 20. Switch to frequency conversion using 20.

On the other hand, the mixer 15 in the main frequency converter 10
If the subsequent circuit section fails, the detection output E3 of the output level detector 19 decreases, the level difference ΔE1 detected by the level difference detection means 30 exceeds a predetermined value, and the
The CPU 44 causes the power control means 50 to switch the power to the auxiliary side. Of course, when an abnormality occurs in the frequency converter, a failure indication is displayed on the display 48, so that appropriate repair measures can be taken.

In the embodiment shown in FIG. 1, abnormality determination is performed by the level difference detection means 30, 32 and the comparison means 34, 38, but each level detection output is used as data/O4.
It is also possible to provide the signal directly to the CPU 44 via the CPU 44 and perform abnormality determination under program control in the CPU 44.

(Effects of the Invention) As described above, according to the present invention, the level difference between the mixer input level and the output level of the main frequency converter is monitored, and the mixer input level of the main frequency converter and the auxiliary frequency converter are monitored. The system monitors the level difference between the mixer input levels, and when the level difference on either side falls outside of a predetermined range, it is determined that there is an abnormality and the system switches to the auxiliary frequency converter, greatly improving the reliability of the frequency converter. can do. Furthermore, even if there is a no-signal state in which the terminal device does not send out a signal, as in the CSMA system, it is possible to reliably detect an abnormality in the frequency converter and perform backup switching.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a two-way CATV system using the frequency conversion device of the present invention. 1: Head end, 2: CATV line, 3: Bidirectional amplifier, 4: Terminal device, 5, 6: Brancher,
7: Frequency converter, 8: Distributor, 10: Main frequency converter, 11, 17, 21, 27: Band pass filter, 13, 23: Low amplifier, 14:
PLL local oscillator, 15, 25: mixer, 16,
26: High amplifier, 18: Input level detector (first input level detector), 19: Output level detector, 20: Auxiliary frequency converter, 28: Input level detector (second input level detector), 30,3
2: Level difference detection means, 34, 38: Comparison means,
36, 40: Reference voltage source, 42: Data/O,
44: CPU, 46: ROM/RAM, 48: Display, 50: Power supply control means, 52: Local control means.

Claims (1)

[Claims] 1. A television signal is transmitted from the head end to the terminal device, and an information signal using a predetermined uplink frequency is transmitted from the terminal device to the head end side, and the information signal is converted to a predetermined downlink frequency at the head end side. Bidirectional frequency conversion and transmission to other terminal equipment
A frequency conversion device for a CTV system includes a main frequency converter and an auxiliary frequency converter that convert the upstream frequency to a downstream frequency, and a first input level detector that detects an input level to the mixer of the main frequency converter. an output level detector that detects the output level of the mixer of the main frequency converter; and a second input level detector that detects the input level to the mixer of the auxiliary frequency converter.
a first level determining means for determining whether or not a difference between the input and output levels of the main frequency converter between the first input level detector and the output level detector is within a predetermined value; and the first input level detector. and second level determining means for determining whether or not the detected input level difference of the second input level detector is within a predetermined value; 1. A frequency conversion device for a double-high CATV system, comprising a switching control section that controls switching from a main frequency converter to an auxiliary frequency converter when a discrimination output that deviates from a value is generated.