Portable and low cost optical line tapping device for network health monitoring solution.
The broadcasting system used in Malaysia is the satellite system. Broadcasting satellite system has many weaknesses and it is more significant during rain, storms and so forth. For example, on rainy days, the receiving satellite signal using the antenna is not so good due the influence of weather conditions. However, if the satellite system is replaced with the cable system, it is found that although it was raining, but the signal reception is better. If the cable system uses optical fiber as its medium of signal propagation, hence the television system can provide a better service to the consumers. In addition, the optical cable system will also provide good and high quality services for voice and image broadcasting. Optical cable is also capable to carry many channels at the same time (greater bandwidth). Based on cable system criteria, it is proven that cable system is better than satellite broadcasting system. However, cable system still has the disadvantage that it may suffer damage. In fiber optic system, laser radiation which is the carrier operates in the range of invisible light and this radiation exposure can cause retinal burns and subsequently permanent blind (Ab-Rahman et al., 2009a). Apart from that, optical fiber is also brittle and can easily be broken if there is a strong external force. Hence, to avoid any accident, the cable status should be monitored constantly.
In order to identify whether the cable system is in good condition or not, a video signal measurement system has been designed and constructed to test the received video signal. After observing the video signal and displaying the image on a measurement tool, an analysis can be conducted. This analysis will determine if the system is in good condition or not. If the displayed video signal is in bad condition it is predicted that there are faults from the main cable line system. This measurement device is also important in network restoration mechanism that serves to divert to alternative routes signals in cables (Ab-Rahman et al., 2009b; Ab-Rahman et al., 2011b; Aziz et al., 2009). Many studies have been done regarding protection architecture in optical network (Ab-Rahman et al., 2011a). Besides that, the best technique to monitor the status of FTTH optical network has also been investigated (Ng et al., 2009; Ab-Rahman et al., 2010; Premadi et al., 2009).
This measurement tool which is the CATV tester will be used to identify video signal condition when there is any disruption to the video signal of the television channel. In summary, this measurement tool will be connected to a device tapper. This tapper is located between the optical line terminal (OLT) and optical network terminal (ONT). The tapper allows the transmission of continuous signals to consumers from the main system and at the same time, it enables the CATV tester tool to test video signals. This means that the tapper will be tap 10 percent of the original signal to be used by CATV tester tools as input to the optical line terminal (OLT). CATV tester tool is also a video signal receiver and also used as a video signal tester. There are several types of signals carried by the Fiber-to-the-home (FTTH) main system. Before the signal is sent directly to the consumers, all signals will be combined into one signal using Wavelength Division Multiplexing (WDM) technique. The signal will be transmitted using a single optical fiber. The signal on a single optical fiber is known as fiber signal (Cleary 2005). Fiber signal will enter the tapper device and then enters the CATV tester as the input. Fiber signal which is the input of the CATV tester has a wavelength range of 1550 nm for video signal and 1310 nm for data and audio signals. CATV tester will separate the received signal to 1550 nm video signal and 1310 nm for audio and data signals. Next the video signal at 1550 nm will be tested by using CATV tester measurement system. The process of designing, building and testing tools CATV Tester involves four phases of the theory and design of the system, the installation of the system, testing of the system and the packaging of the system.
The prototype developed is CATV measurement tool for fiber-to-the-home (FTTH) network system. This system serves as a system that can monitor whether the signal is in good condition or not. This tool can be used when there is any disruption to television channel guide. The main function of this tool is to test video signal at a wavelength of 1550 nm. The wavelength of data, voice and video received by the system will be separated. Only the signal at 1550 nm wavelength will be taken and observed by this system. This system consists of hybrid components which is passive and active. Some of the passive components are Wavelength Division Multiplexer (WDM) and fused coupler. The active components consist of the video transceiver and mobile TV.
Operating System Block Diagram:
Figure 1 shows the block diagram for the CATV testing unit used to determine the status of optical fiber using the analysis of video signal transmission. Passive circuit and active components are used to obtain the video signal so that it can be observed by television. Passive circuit is used to separate video and data signals and it only takes a few percent of the video signal to be observed. Therefore, this system requires a component that can separate the video signal and the data signal from the main cable. After the signal separation, the desired signals are separated by a fixed ratio. The ratio used for this project is 90:10. 10% of the signal will be used to see if the line is in good condition or not. The remaining 90% of the signal will be driven directly to a component that can combine the video and data signals and the signal will be sent to the customer. A converter is used to converts optical signals into electrical signals and thus it can be used by mobile TV. Passive optical components consist of passive devices; the coupler and the Wavelength Division Multiplexer (WDM). The operation principle of this system is that the input signals will enter the WDM (1310/1550 nm) from the main cable line and will be linked directly to the CATV control unit. This WDM input signal will enter the WDM 1310/1550 nm. Here, WDM signal will be multiplexed. Data signal at a wavelength of 1310 nm will enter WDM, while the video signal at a wavelength of 1550 nm will enter 90:10 fused couplers. 90% of 1550 nm signal will be sent and multiplexed again with 1310 nm data signal. The remaining 10% of 1550 nm signal will be used as the CATV control signal. This signal is used as the input signal of the receiver. This video converter will convert the optical signal to RF analogue signal and eventually the signal can be seen using mobile TV.
[FIGURE 1 OMITTED]
Voltage Regulator Circuit:
Voltage regulator circuit is designed as in Figure 2 so that the optical signals to RF converter, LCD TV and fans can share the same power supply. The components are:
i. Resistors: 1kohm
ii. Capacitors: 2200[micro]F and 470[micro]F
iv. Voltage regulator: 78H12
The power supply for the input signal to the RF converter will be placed at the input of the voltage regulator circuit while the mini LCD TV and fans will be placed at the output voltage regulator circuit.
[FIGURE 2 OMITTED]
Voltage Regulator Circuit--In General:
Voltage regulator circuit is used to generate the voltage of 12V and 5V. The circuit is installed separately after considering the total value of the current that flows in each circuit. This is because the Mini LCD TV is sensitive. The total current entering the Mini LCD TV should be adequate as indicated by the spec (I~1.5A) so that no interruption in TV broadcasting. 12V regulator circuit will be used as a source of power supply to the Mini LCD TV. While the regulator circuits that produces 5V will be a source of power supply to the fan. The main power supply for both circuits is 15V ac (2A-4A). A basic voltage regulator circuit is shown as in Figure 3.
[FIGURE 3 OMITTED]
12V Voltage Regulator Circuit:
Before the actual voltage regulator circuit is built; the circuit was simulated using circuit maker software. Components involved in this circuit are:
i. Signal generator 15V 1kHz
ii. 1 wheat stone bridge
iii. 2 capacitors (470 [micro]F and 0.01[micro]F)
iv. Chip regulator 7812
Signal generator will act as the source that supplies power to the circuit. Signal generator will be functioned at 15V, at frequency of 1 kHz. The signal generated by signal generator will be rectified using the wheat stone bridge to convert the alternating current into direct current. This is the process of converting a voltage with alternating current to the voltage with direct current. There is a different in output voltage compared to the previous research work whereas the desired output voltage is 12V dc. In general, it can be concluded that it will use the same concept. For the implementation of the actual situation, this voltage regulator circuit uses UA78H12 component after LM7812 component failed to function properly. LM7812 is a component that can easily get hot and release heat in large quantities. These features will result in the vicinity of the LM7812 is exposed to heat. This situation affects the fiber that is sensitive to heat. This shows that the LM7812 components are not suitable for generating a voltage to be connected to a mini LCD TV that requires the input voltage of 12V dc. Thus a UA78H05 chip regulator will be used to replace the LM7805. However, since there is no UA78H12 component in the software circuit maker, then the voltage regulator circuit analysis will be using the LM7812 as regulator chip. The following is the analysis of circuit maker software to simulate the voltage regulator circuit.
[FIGURE 4 OMITTED]
In Figure 4, at point A, the resulting waveform is as shown in the Figure 5 below. This is a sinusoidal wave signal with a frequency of 1 KHz at 15V ac signal generated by the generator. A perfect sinusoidal signal has been generated.
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
The analysis is based on the output of point A, where the voltage regulator circuit with second A point shown as in Figure 6. It was found that there are transient conditions that occur before the signal is rectified to be stable. After the signal is rectified by the wheat stone bridge, the signal has arise time, [t.sub.r] up to t [approximately equal to] 0.2 ms before it reaches the 90% of the value of a stable voltage. After a time t [approximately equal to] 0.8 ms, the signal began to straighten to the actual voltage stability. At time t [approximately equal to] 0.8 ms, it is known as the settling time, [t.sub.s]. At a later time, the voltage will be stable between [+ or -] 2% and [+ or -] 5% of the steady state value. Figure 7 is the resulting signal after the signal is rectified by a wheat stone bridge using Silicon diode.
[FIGURE 7 OMITTED]
Next is the analysis at point A, after the rectified signal is filtered with a filter. This filter will filter all the remaining ac that is not rectified. From Figure 8, it is found that the voltage that has been filtered will have a smoother signal and the resulting waveform on this condition is shown in the Figure 9.
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
The next stage is that the signal will enter the LM7812IC regulator. Here the output voltage will be reduced from 12V from 13V (voltage drop).
[FIGURE 10 OMITTED]
This value is based on simulation analysis as shown in Figure 10. In the IC regulator there is a ground for grounding the input voltage that may not be rectified. This is because the bridge and filter capacitor voltage is likely to allow the unregulated dc voltage with a cripple voltage be the input to voltage regulator. By grounding the ac ripple, the output voltage of the IC regulator can be maintained at the required specifications. Regulator IC output voltage through the capacitor which in turn serves as a filter that will filter out high frequency noise. As a result, the waveform is as shown in the Figure 11.
[FIGURE 11 OMITTED]
Thus the output voltage in the circuit will be smoother. The resulting circuit will be used to supply power to three devices which are; video transceiver, Mini LCD TV and fans.
5V Voltage Regulator:
The function of this circuit is just like the 12V voltage regulator circuit and the different is the output of this circuit is 5V only, as shown in Figure 12.
[FIGURE 12 OMITTED]
Design For Detecting Stability:
In the design of Portable Video Tester Equipment the prototype for the 'Fiber to the Home' (FTTH) network, Hilev Technology Sdn. Bhd. has carried out several testing procedures to ensure that the components meet the specification that has been set. The passive components in the 'Portable Video Tester Equipment' product are 'Fiber Optics' which contains of OLT (Optical Line Terminal/Termination), ONU (Optical Network Unit) and the splitter. On the other hand, the active or electrical components are 'Converter', Mini LCD TV, Adapter, Fan and 12V dc regulator voltage circuit. Before the product can be produced without any defect, the components are tested in several testing procedures which are:
Testing of The Circuit on the 'Bread board:
The DC voltage circuit was tested using a function generator to ensure that the displayed output voltage from IDL is +/- 12V dc when an input voltage of 15V dc 4A is applied. The (+/-) 12V dc is to be supplied to the Mini LCD TV while 5V dc 1A is used to run 3 fans. Figure 13 shows the circuit under test.
[FIGURE 13 OMITTED]
All of the components that are connected on the circuit were tested using a multimeter to detect any voltage and current downfall. The multimeter is also used to measure the voltage and current value of each component. If there is no reading on the multimeter when a component is tested, the component maybe faulty hence requires replacement.
Testing on the Converter Test:
The converter was tested by connecting the OLT from the Main Central to the Converter and from the Converter to the Television. If the signal displayed on the Television screen is blurring, it means that the Converter did not converted the light signal from Fiber Optics to electrical signal perfectly. Figure 14 shows the installation of 'Converter' in the CATV Tester Unit.
[FIGURE 14 OMITTED]
Testing on the Mini LCD TV:
This test is to confirm if the Mini LCD TV is able to display a clear image signal when searching for channel frequency. If there is a distortion in the signal after the input voltage is applied, it means that the supply voltage and current are not enough for the Mini LCD TV hence degrading the image signal. Figure 15 shows the testing of CATV Tester Unir using a bigger TV screen for better observation on the quality of the video signal received.
[FIGURE 15 OMITTED]
Testing on Fibre:
There are 2 types of device that were used to measure the Insential Loss of each fibre which are Optical Spectrum Analyzer (OSA) and Turnable Laser Source. These devices use Petch Code as the cable to connect the input fibre with the output fibre. Normally, the OSA has a filter which produce testing results in a shape of its own spectrum. Broadband resolution is an important parameter as it reflects the small specturm operation when the OSA is filtering -3 dB signal. Despite of a limited power as low as -20 dB, the broadband resolution has shown that the filter is still able to measure the reading smoothly without noise and dispersion. The reading of the output specturm needs to be less than 5 dB when it is deducted from the reference value. If the Insential Loss exceeds 5 dB, the fibre is faulty hence needs to be replaced. Before testing, the wavelength reference value of the 'Turnable Laser Source' needs to be 1550nm/1310 nm.
Testing on Fan:
The fans used in the system are to absorb the extra heat from the Mini LCD TV and the dc voltage regulator circuit board. This is to ensure that the extra heat does not affecting the laser performance since the components will be close to each other and in the same space. The temperature range for laser of Fused Coupler (SPLITTER) type is +0 [degrees]C to +65 [degrees]C and -20 [degrees]C to +70 [degrees]C for Optical WDM type. In order to test if the fans are working, 9V battery is used to turn it on. If the fans are working, a blue LED will light up and the fans will rotate. Figure 16 shows the installation of fans used to surpress the heat produced and increase the lifetime of the electronic circuit in the CATV Tester Unit.
[FIGURE 16 OMITTED]
Maintenane can be a good solution to detect any damage or weaknesses on the devices/components. The easiest way to analyse a result is based on the flow chart on Figure 17. Figure 18 shows briefly the maintance steps to test the voltage circuit board. Mantainece steps to test the Converter is shown in Figure 19.
Results And Discussion
From the results obtained in this project, the specification of the Fiber Optic that can be used for Splitter are 50:50, 90:10 and 95:5 where the optical signal is devided evenly i.e. 50-50 between the user and signal tester (engineer), for 90:10, 90% signal is received by the user and 10% is tested and similarly, for the type 95:5, 95% is received by the user and only 5% is tested. Every ratio value of the Fused Coupler used to split the signal gives a different quality signal on the TV screen. The higher splitting percentage ratio, the better signal is displayed. However, as a signal tester, Fused Coupler does not need a high splitting ratio. 10% is enough because the function of this product is just to ensure the user receive the transmitted signal else there might be some damages on the fibre.
The capability of the converter in converting the optical signal to electrical signal is proved by the image exit from the converter to the Mini LCD TV. When the display appeared on the TV screen and a red LED is light up, this proves that the Converter is working. Otherwise, the TV screen is will still showing an output signal but it is due to the Radio Frequency (RF) signal. The dc voltage regulator circuit board used for the CATV has an output voltage of 12V dc and 1.5A which is to be supplied to the Mini LCD TV, 5V dc, 0.4A for the 3 fans and 15V ac, 1A to switch on the converter. The configuration of the d.c voltage circuit board must be able to provide enough voltage and current to the three loads through out the duration of operation.
[FIGURE 17 OMITTED]
[FIGURE 18 OMITTED]
[FIGURE 19 OMITTED]
[FIGURE 20 OMITTED]
[FIGURE 21 OMITTED]
[FIGURE 22 OMITTED]
Figure 20 shows the prototype of the CATV Tester Unit that has been produced. In order to ensure the CATV unit is working, system test was carried out by testing the FTTH network as in Figure 21. Figure 22 is the diplayed image that was received during the test by only mesuring 10% of the video signal from the original signal sent through the network.
As a conclusion, this project has met its objectives which are to understand the method and principle behind the operation of a CATV signal testing system and produce a system to test CATV signal for a FTTH network. The CATV video signal was received and the image was displayed by the portable TV. With this system, it is hoped that it will meet the demand of the current high speed technology. The system that was developed has several advantages such as the system is able to measure the video signal where the image can be seen clearly on the portable TV.
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Corresponding Auther:Mohammad Syuhaimi, Spectrum Technology Research Group (SPECTECH), Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bandar Baru Bangi, Selangor
Mohammad Syuhaimi Ab-Rahman, Suria Che Rosli, Nani Fadzlina and Nur Hasiba Kamaruddin
Spectrum Technology Research Group (SPECTECH), Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bandar Baru Bangi, Selangor.
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|Title Annotation:||Original Article|
|Author:||Ab-Rahman, Mohammad Syuhaimi; Rosli, Suria Che; Fadzlina, Nani; Kamaruddin, Nur Hasiba|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Nov 1, 2011|
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