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HFC11.0 Fundamentals of HFC

HFC11.0 Fundamentals of HFC. Agenda. Basics – AC, DC, Ohm’s law, Units and measurements. Log, Antilog, why use them loss, gain, power level units? dB, dB μ V, dBmV, dBm and their conversions. Passives, types of passives, functions of different passives.

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HFC11.0 Fundamentals of HFC

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  1. HFC11.0Fundamentals of HFC

  2. Agenda • Basics – AC, DC, Ohm’s law, Units and measurements. • Log, Antilog, why use them loss, gain, power level units? • dB, dBμV, dBmV, dBm and their conversions. • Passives, types of passives, functions of different passives. • What is network? Different network architectures. • Homes passed, homes connected. • What is HFC network. • Fundamentals of fiber optics. • Various losses in fiber link. • Fiber optic hardware, cables, and accessories. • Commonly used measurement techniques. • Use of multi-meter and signal level meter (dB meter). • Use of spectrum analyzer. • Loss calculations and signal level estimation in network segments. • Symbols used for Network hardware. • Hands on practice. • Field visits. • Theory and practical test. • Grade allocation.

  3. Alternating current (AC), Direct current (DC) AC voltage • There are two types of voltages you will be coming across in the network. • AC voltage continuously changes with time as shown in the figure. • The power supplied by electricity board has a voltage which is AC. • The voltage measured by a meter on the three pin power socket (between 230 to 240 volts) is called R.M.S. (Root Mean Square) voltage which is sort of an ‘average’ voltage. • http://www.yenka.com/freecontent/attachment.action?quick=14y&att=2937 Voltage Amplitude Time

  4. RMS explained Peak • For example: suppose the time samples are as shown in the diagram: Values: 0 7 10 7 0 -7 -10 -7 Squares: 0,49,100,49,0,49,100,49 Sum of squares = 396 Average of squares = 396/8 = almost 50 Square root ~ 7 7 = 0.7 x 10 (peak voltage) With more intervals the r.m.s. average turns out to be (peak value) / √2 = peak value/1.41 = 0.707 x peak value RMS = 0.707 x peak 325/1.41=230V RMS

  5. Sine wave 1 cycle • A Sine wave is a periodic signal. • A clock pendulum is an example of periodic motion. • A Sine wave is also a fundamental signal. • All wave forms encountered in real life are made of combination of number of sine waves. • When signal goes through all possible variations and comes back to the next starting point, one cycle is completed. • Number of cycles per second is called Frequency. It is measured in Hertz (Hz). Frequency of power is 50 Hz. • As an example, starting from 6 a.m. today to 6 a.m. tomorrow is one day cycle. • Similarly we can have a one year cycle. 1 cycle

  6. Voltages on 3 pin power socket E 230 V Approx 0 to 3 V L N 230 V Approx Front view of mains socket Color code for wires Indian code L = Red N = Black E = Green European code L = Brown N = Blue E = Green + white L = Line terminal N = Neutral terminal E = Earth terminal

  7. Top plug connections • The picture shows Line, Neutral and Ground connections. • There is a fuse in the line terminal for over current protection. Ground Line Neutral Back view of a top plug

  8. Batteries and DC voltage • A source of DC voltage is a battery. • Batteries are used in conjunction with a UPS (Un interruptible Power Supply unit) to maintain power in a network when electricity board power (Grid power) is unavailable due to a fault or load shedding. • Batteries come in different voltages, sizes, shapes and in technologies. • Batteries used in a CATV network can be of 12 or 24 volts, maintenance free or tubular which requires water topping periodically. • The size of a battery depends on the time it can give a back up to maintain power in the event of power outage. It is specified in Ampere-Hours (AH). 65 and 100 AH batteries are most commonly used in a CATV network. Size of a battery will increase as AH rating increases.

  9. Voltage 12 Volts Time Batteries and DC voltage Battery symbol • A Battery voltage is constant. • It does not change with time like AC voltage. • Voltage, however, will drop when batteries get discharged. • Batteries can be connected in series to increase voltage or in parallel to increase AH. • All electronic devices like lap top, mobile, TV, radio, music system work on DC voltage. • We need a power adaptor for charging batteries of battery operated devices such as mobile or lap top. • Devices working directly on 230 V AC have an internal power supply to convert AC voltage to DC voltage. Positive terminal Negative terminal 12 V, 65 AH battery Battery discharge Series connection: 48 V, 65 AH Battery bank Parallel connection: 24 V, 130 AH Battery bank

  10. Converter/Inverter • A Converter converts AC voltage to DC Voltage. • An Inverter converts DC voltage to AC Voltage. • A UPS has both a converter and an inverter built into it. • When grid power is available, it will convert AC to DC and charge the batteries while powering the network also. • When grid power fails, it will take DC from batteries and converts to AC to continue powering the network. • Typically the batteries will give a back-up of 2 to 3 hours, depending on battery condition. • One end of AC supply and the negative terminal of DC supply are normally grounded in a CATV network as shown. • The co-axial cable outer conductor is grounded and acts as a return conductor. + DC voltage AC voltage _ Converter + DC voltage AC voltage _ Inverter

  11. Voltage, resistance, current, power and Ohm’s law Open circuit, Very large resistance of air, No current. • Current in Amperes = Voltage in Volts/ Resistance in Ohms I = V/R • Power in watts = Voltage in Volts x Current in Amperes P = V x I Also P = (I x R) x R = I2 x R • From Ohm’s law, we can have following equations: • I = V/R • V = I x R • R = V/I • P = V x I • P = I2 x R • P = V2/R • 1 unit of electricity = 1 Kilowatt hours (KWH) 12 V battery Short circuit, Zero resistance Heavy current with sparks. Load connected, Current depends on load in watts If the bulb is of 30 watts, then 30 = 12 x I I = 30/12 = 2.5 Amperes. Current flowing through the bulb is 2.5 Amps.

  12. Examples • If V = 24 volts, R = 6 ohms then I = 24/6 (V/R) = 4 amps and P = (24)2/6 (V2/R) = 576/6 = 96 watts. • If V = 24 volts, I = 4 amps then R = 24/4 (V/I) = 6 Ohms and P = 24 x 4 (V x I) = 96 watts. • If I = 4 amps, R = 6 Ohms then V = 4 x 6 (I x R) = 24 volts and P = 42 x 6 ( I2 x R) = 16 x 6 = 96 watts.

  13. I μA = I Amp x 1000,000 I mA = I Amp x 1000 V μV = V Volt x 1000,000 V mV = V Volt x 1000 P μW = P Watt x 1000,000 P mW = P Watt x 1000 I Amp = I μA/1000,000 I Amp = I mA/1000 V Volt = V μV/1000,000 V Volt = V mV/1000 P Watt = P μW/1000,000 P Watt = P mw/1000 μa, ma, A, μV, mV, V, μW, mW, W

  14. 100 = 1 101 = 10 102 = 100 103 = 1000 Log 1 = 0 Log 10 = 1 Log 100 = 2 Log 1000 = 3 Antilog 0 = 1 Antilog 1 = 10 Antilog 2 = 100 Antilog 3 = 1000 Find log Find anti-log Logarithm (Log), Antilogarithm (Antilog)

  15. 100 x 10 = 1000 Log 100 = 2 Log 10 = 1 Sum of Logs = 2 + 1 = 3 Antilog 3 = 1000 1000/100 = 10 Log 1000 = 3 Log 100 = 2 Subtraction of logs 3 – 2 = 1 Antilog 1 = 10 Multiplication, division of numbers Multiplication of two numbers is the sum of their Logs Division of two numbers is the subtraction of their Logs

  16. Why Log, Antilog? • There are 2 advantages in using logarithmic unit. • First, as we have seen, multiplication function gets converted to addition and division function gets converted to subtraction. • Because of this conversion, as you will see later, we can add gain and subtract losses when we are estimating signal level at different points in network segments. The whole process becomes very simple. • Second, large numbers get transformed to small numbers e.g. log of 100,000 is 5. A 6 digit number has transformed to 1 digit. • In a cable network one can encounter signal levels from 100 μV to 1000,000 μV (1V). When converted to dBμV, they are 40 dBμV to 120 dBμV – manageable numbers.

  17. Ratio and Decibel • A ratio compares one number against another number. • If a son is weighing 40 Kg. and the father is weighing 80 Kg. then the father is 80/40 = 2 times heavier than the son. • The number 2 does not indicate absolute weight of either the son or the father (40 and 80 Kg). • If an amplifier input signal power is 10 mw and the amplified output power is 100 mw then output power is 100/10 = 10 times higher than the input power. • The number 10 does not indicate absolute power at either the input or the output (10 and 100 mw). • Similarly Decibel is a comparison of two signal power levels. • This comparison can be against input power level or any reference power level we may choose.

  18. 10 x Log Pout/Pin If Pout is 100 mw and Pin is 10 mw Then dB = 10 x Log 100/10 = 10 x Log 10 = 10 x 1 = 10 dB Pout is 10 dB greater than Pin Pin can also be a reference power and is generally 1 mw. 20 x Log Vout/Vin If Vout is 100 mV and Vin is 10 mV Then dB = 20 x Log 100/10 = 20 x Log 10 = 20 x 1 = 20 dB Vout is 20 dB greater than Vin Vin can also be a reference voltage and is generally 1 μV or 1 mV. Decibel (dB) Decibel is the Log of ratio of voltages across same value of resistor Decibel is the Log of ratio of Powers

  19. dBμV, dBmV, dBm • dBμV indicates that our reference voltage is 1 μV . • Thus, 1000 μV is 20 Log(1000 μV/1 μV) = 20 Log 1000 = 20 x 3 = 60 dBμV. • 60 dBμV means that power delivered by 1000 μV in a resistor is 60 dB greater than power delivered by 1 μV in the same resistor. • dBmV indicates that our reference voltage is 1 mV. • Thus, to convert 1000 μV in to dBmV, first convert 1000 μV to mV. • 1000 μV = 1 mV. • 20 Log 1 mV/1 mV = 20 Log 1 = 20 x 0 = 0 dBmV. • 0 dBmV means that that power delivered by 1mV (1000 μV) in a resistor is 0 dB greater than power delivered by 1 mV in the same resistor. • Thus we can say that 0 dBmV = 60 dBμV.

  20. dBμV = dBmV + 60 30 dBmV = 90 dBμV 55 dBmV = 115 dBμV -10 dBmV = 50 dBμV -25 dBmV = 35 dBμV dBmV = dBμV – 60 60 dBμV = 0 dBmV 75 dBμV = 15 dBmV 40 dBμV = -20 dBmV 55 dBμV = -5 dBmV Similarly we can prove that for a 75 Ohm system: dBμV = dBm + 108.75 dBm = dBμV – 108.75 dBmV = dBm + 48.75 dBm = dBmV – 48.75 dBmV dBμV dBm conversion

  21. Passives: what do they do? • Signal distribution on HFC network can be compared to water distribution in a city. We can say that our ultimate objective is to distribute water to all the households within certain pressure limits irrespective of their location. • For this we need to have pipes of suitable diameters with valves and pressure regulators installed at correct locations. • Each household needs only a small portion of water that is flowing in the main pipe. • Similarly, each household requires only a small portion of a signal that is flowing in the trunk cable. Also the signal should be within certain strength (60 to 80 dBμV) irrespective of the locations of households. • Clearly, we need some devices which will distribute and control the amount of signal to households. They are called passives.

  22. Passives • Passives are used in the HFC distribution network to manipulate and distribute signal in the desired direction and proportion (power level). • The word ‘Passive’ signifies that the passive devices do not require power for their functioning. As opposed to a ‘Passive’, an ‘Active’ device such as an amplifier requires power for it to work. • Directional coupler, splitter, tap-off, power inserter, diplex filter, noise blocker, attenuator, terminator (Dummy load) are the passives used in a distribution network. • Passives are made by using inductors, capacitors, resistors and R.F. transformers wound on ferrite material. • A Passive is specified for the frequency range it can work for and losses between its various ports. • All passives are designed for Input/Output impedance (Zo) of 75 Ohms.

  23. Directional coupler (DC) • A directional coupler (DC) divides the signal unequally - major portion going to the output port, and only a small portion (design value) going to the coupled port. • It couples a desired (by design) amount of signal to its coupled port from its input port. • It comes in 8 or 12 dB coupling loss. An 8 dB coupler will have the signal level at the coupled port 8 dB lower than the input port level. This is called as ‘Tap loss‘ or ‘Coupling Loss’. • Loss between Input and Output ports is called ‘Insertion loss’ or ‘Through loss’. • Loss between Output port and Coupled port is called ‘Isolation’. • Power can be made to pass through all the ports. • SSP-7N, SSP-9N and SSP-12N are examples of a DC which give 7, 9 and 12 dB loss between IN and TAP ports. SSP-7N

  24. Directional coupler as a signal combiner • A directional coupler can also be used as a signal combiner. • In the example shown, signal source1 is connected to the OUT port of a SSP-7N. • Signal source2 is connected to the TAP port of the SSP-7N. • Signal 1 will suffer insertion loss of 2 dB and signal2 will suffer tap loss of 7dB. • After combining, signal2 will be 5dB lower than signal1. • If you wish to have both, signal1 and signal2 levels to be the same, you need to have signal2 level at 105 dBμV so that at the IN port both signals will be 98 dBμV. Signal 1 + signal2 SSP-7N Signal source 1 In Out 98dBμV + 93dBμV 100 dBμV Tap Signal source 2 100 dBμV

  25. Use of a DC • Typically, a DC is used at the output of a node or an amplifier or on a trunk. • When the network needs to be split to cover two different areas and where one cable jump is long and the other is short, a DC is used. 8 or 12 dB DC Long cable jump More signal Amplifier Short cable jump 8 or 12 dB less signal

  26. Typical losses in a DC • In all the Directional Couplers, as frequency increases, loss increases by 1 to 2 dB. • As the DC value increases from 8 to 12 to 16, the insertion loss decreases.

  27. Splitters • A splitter divides the signal equally. The input signal is divided in to 2 or 3 outputs. • 2 way splitter has 4 dB loss between their input and output ports. This is called as ‘Splitting Loss’ or ‘Insertion Loss’. • Loss between the Output ports is called ‘isolation’ • 3 way splitter has 2 ports with 8 dB loss while 1 port with 4 dB loss. • Power can be made to pass through all the ports (outdoor type only). • Indoor varieties can have 1 input and 2/4/6/8 output ports. SSP-636N SSP-3N

  28. Use of a 2 way splitters • Typically, a 2 way splitter is used at the output of a node or an amplifier or on a trunk. • When the network needs to be split to cover two different areas and where both the cable jumps are approximately equal, a 2 way splitter is used. Approx. 2 equal cable jump 2 way splitter Amplifier

  29. Use of 3 way splitters • Typically, a 3 way splitter is used at the output of a node or an amplifier or on a trunk. • When the network needs to be split to cover three different areas and where two cable jumps are approximately equal and short while the third jump is long, a 3 way splitter is used. Approx. 2 equal short cable jumps Long cable jump 3 way splitter Amplifier

  30. Typical losses in 2 way and 3 way splitters • As the frequency increases, losses increase by 1 to 2 dB.

  31. Splitter used as combiner • A splitter can work as a combiner, if it is used in reverse. It means that to make a 4 way combiner, one has to feed signals to the output ports of a 4 way splitter and get combined output in the ‘Input’ port. Indoor 4 way splitter

  32. Tap-offs • The picture shows a 2 way tap diagram. • A tap-off is a combination of a DC and a splitter. • Signal loss between the Input port and the Output port is called ‘Insertion’ or ‘Through’ loss. • Signal loss between Input and any tap port is called ‘Tap loss’. This loss is a designed loss and can be between 4 to 32 dB, in steps of 3 dB. • We need different tap values because we need to feed equal amount of signal (60dBμV) to all the customers irrespective their location from the serving amplifier. • Customers nearer the amplifier will be fed through high value taps while the ones away from the amplifier will be fed from low value taps. Symbol

  33. Tap-offs • Signal loss between Output port and any tap port is called ‘Isolation’ and is greater than 20 dB. • Signal loss between any two tap ports is called ‘Tap to tap isolation’ and is greater than 20 dB. • The picture shows a 4 way tap-off diagram. • 2way, 4way, 8way tap-offs come in Outdoor and Indoor variety. • In the Outdoor type, there is power passing facility between In and Out ports. But usually there is no power passing on the tap ports. However, recently tap-offs with power passing facility on tap ports with protection fuses are available. • Generally, there is no power passing facility on any of the ports in the Indoor type. Symbol

  34. Indoor tap verities

  35. 2, 4, 8 way outdoor tap-offs

  36. Typical losses in 2 way Tap-offs • As the frequency increases, Insertion loss increases by 1 to 2 dB. • As the tap value increases, Insertion loss decreases. • 4 dB tap is a terminating tap – meaning the Output is terminated internally with 75 ohms and therefore, there is no external Output port.

  37. Typical losses in 4 way Tap-offs • As the frequency increases, Insertion loss increases by 1 to 2 dB. • As the tap value increases, Insertion loss decreases. • 8 dB tap is a terminating tap.

  38. Typical losses in 8 way Tap-offs • As the frequency increases, Insertion loss increases by 1 to 2 dB. • As the tap value increases, Insertion loss decreases. • 11 dB tap is a terminating tap. • As the number of tap ports increase from 2 to 4 to 8, for the same tap value Insertion loss increases. • A 14 dB 2 way tap has an insertion loss of 1.8 dB at 450 MHz, 4 way has 2.5 dB and 8 way has 4.1 dB.

  39. Line power inserter (LPI) • Line power inserters are used for injecting 90 V A.C. voltage from a power supply into a trunk cable route to power a node and amplifiers. Signal and power are combined on such a cable. They normally come in outdoor type only. SSP-PIN UPS 230V

  40. Power/signal filter in LPI AC VOLTAGE BLOCKING CAPACITOR SIGNAL SIGNAL + AC 40~90 V RF AC 40~90 V RF BLOCKING CHOKE POWER

  41. Rubber and wire mesh gaskets • In all the outdoor passives there are two gaskets which fit between the unit and its base plate. • Rubber gasket prevents rain water entry. • Wire mesh gasket prevents ingress/egress. • You should tighten base plate firmly by tightening the four bolts. • Install tap-offs so that tap ports face the ground. This will prevent rain water entry in to tap ports. • Tighten all check nuts to prevent rain water entry.

  42. Diplex filter Plug in units for node and amplifiers Head end unit • Diplex filters are used to either combine or to separate the downstream (54 –860 MHz) and upstream (5 – 40 MHz) signals. • In a 2 way network a diplex filter is installed at every Output of a node and at the Input and every Output of an amplifier. • A Diplex filter is also required at the Headend if Co-ax network is directly fed from the Headend. • The specification of the split of the diplex filter must match with that of your cable network.

  43. Attenuators (5 to 1000 MHz) • Attenuators are used to introduce known loss in the network. They introduce almost uniform loss for all the frequencies from 5 to 1000 MHz. • Many a times, signal level is too high for a network or a customer device. Therefore, we need to reduce the signal level by a known amount. This is done by an attenuator. • Attenuators generally have F male interface at one end and F female interface at the other end. • They come in values from 5 to 25 dB in 5 dB steps or from 3 dB 24 dB in 3 dB steps or from 1 dB to 20 dB in 1 dB step depending on the manufacturer and price. • 5 to 1000 MHz – gives known uniform loss

  44. Return step attenuators (54 to 860 MHz pass) • We use highest tap value for the customers located nearest to the amplifier, gradually reducing the value as we go away from the feeding amplifier. • We do this to equalize the forward path signal (to 60 dBμV) to all the subscribers irrespective of their location from the feeding amplifier. • In the return path also we need to equalize the return signals generated by customer devices (modem) to the same level (105 to 110 dBμV) irrespective of their location from the amplifier. • A Return step attenuator introduces known amount loss onlyin the customer’s Return path, while introducing only 1 dB loss to the Forward path signals. • 5 to 40 MHz – gives known uniform loss (5,10,15 and 20 dB) • 54 to 860 MHz – gives 1 dB uniform loss

  45. High pass filter (54-860 MHz pass, 5-40 MHz block) • In a network catering to the TV and Internet services, there will be some customers who are taking TV + Internet services and some taking only TV services. • Only TV customers don’t require return path. • Noise generated within the homes of only TV customers will enter in the network. • Noise from many only TV homes will accumulate at a node degrading Return SNR. • High pass filters are fitted on the tap ports connected to the drop cables going to the only TV customers, not requiring Return Path. These high pass filters (54 –860 MHz pass) block the noise generated in homes, not using the Return Path.

  46. Terminators (Dummy load, Loader) • A Terminator is a 75 ohm resistor fitted in to a metallic casing which can be fitted on an out door casing or F female connector. • All open ports of nodes, amplifiers and passives must be terminated with a Terminator to maintain network integrity. • If the Terminators are not installed in the network, signal will get reflected from open ports and also noise ingress will take place.

  47. 20 (5) 8(3) 1(1) 8(0) 6(2) 7(5) 5(1) 1(1) 30 (8) 8(0) Homes passed and homes connected Cable run • Homes passed tells us the number of homes (independent homes or apartments in a building) situated along a length of a cable. • Homes passed indicates the number of customers which can be connected to a network for offering services. • Homes passed indicates population density and the business potential of the area. • It has a direct impact on the cost/connection. • If homes passed/km high then cost per connection is low and makes a business case. • Homes connected tells us the number of homes actually connected to a network. • In the example above, Homes passed is 94 and Home connected is 26.

  48. What is HFC? • HFC stands for hybrid fiber Co-ax. • HFC network is built using optical fibers, co-axial cables and associated electronic hardware. • Optical fiber is the medium in which communication signals are transmitted from one location to another in the form of light, guided through a thin fiber of glass. • Co-axial cables, with their special construction, then guide the signal along the metallic conductors on the last mile to the destination.

  49. What is a network? • A network is the way fibers, co-axial cables and the associated hardware pieces are connected. • The main considerations for fiber network are: • Availability of fiber (owned or leased). • Fiber susceptibility to breakage. • Reliability and redundancy requirement. • Cost of laying a fiber cable or leasing Vs business potential. • Signal format – whether IP optical or Amplitude Modulated optical. • Distances to be covered. • Back-up power arrangements. • The main considerations for Co-ax network are signal integrity in the last mile i.e. considerations for noise (C/N) and distortion components (CSO/CTB/XMod) and power outages. • For this reason cascade of amplifiers is limited to 3 or 4 and UPS power back-up is always provided.

  50. Why HFC? • Prior to the emergence of fiber optic technology, networks were built using only co-ax cables. • However, because of unique properties of optical fiber, it is coming ever nearer to home. • It is the best combination for signal delivery in terms of cost, reach, reliability and bandwidth. • Because fiber introduces very low loss to signal, large distances (20 to 50 km) are covered using a fiber to bring signal to a distribution point (Node). • From the node signal is then distributed on co-ax cables to homes covering a radius of 1 km.

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