Friday, January 17, 2020
Design a Repeater for Digital Rf Signal
Abstract Repeaters for digital TV broadcasting can use either analogue or digital techniques. The purpose of using repeater is to boost signals into areas of weak coverage in any radio communication system. However wave interference means the repeater usually requires a frequency shift for analogue modulated signal. For digitally modulated signal it may be possible to use same frequency. This paper investigated and designed a RF repeater which will improve the inter symbol interference by incorporating delay between received and transmit signal.This project also reviewed the basics of current Digital Video Broadcasting-Terrestrial (DVB-T) techniques and selected it as a suitable choice for lab experiment. The practical side of this project is to design and build a repeater incorporating suitable electrical delay. Contents 1. 0 Introduction4 1. 1 Background:4 1. 2Aim of this project6 1. 3Project objectives6 1. 3 Project deliverable7 2. 0 Problem analysis8 2. 1 Repeater8 2. 1. 1 Analog ue repeaters9 2. 1. 2 Digital repeaters10 2. 2 Inter symbol interference13 2. 3 Multipath propagation15 2. 3. 1 Multipath fading15 2. 4 The TV channels16 2. 5 Transmission cable18 . 6 Signal Amplifiers20 2. 7 Transmission delay (Coaxial cable)21 3. 0 Possible solution24 3. 1 RF amplifier25 3. 1. 1 The Transistor Amplifier26 3. 1. 2 Ultra High Frequency Transistor Array (HFA)29 3. 1. 3 Surface mounts technology:32 3. 1. 4 Surface Mount Monolithic Amplifier:32 3. 1. 5 Loft box: 8 way home distribution unit34 3. 2. 6 Maxview signal booster35 3. 2. 7 Antenna:36 4. 0 Design37 4. 1 Circuit design37 4. 2 PCB design38 5. 0 Implementation40 5. 1 Implementation with HFA312740 5. 2 Implementation with MAV-11SM amplifier41 6. 0 Test result42 6. 1 Laboratory test result42 6. 2 Field test result44 7. Result Discussion46 8. 0 Conclusion48 Future work:49 Works Cited50 Figure List Figure 1System block diagram6 Figure 2 Passive and Active repeater block diagram7 Figure 3 Analog repeater8 Figure 4 Dig ital repeater9 Figure 5 Channel management for digital repeater10 Figure 6 Channel management for analogue repeater10 Figure 7 Broadcast in valley with digital repeaters11 Figure 8 101101 transmitted data12 Figure 9 Received data12 Figure 10 Transmitted data vs. Received data13 Figure 11 Multipath propagation14 Figure 12 Cable loss in dB  (Antenna basics, 2008)18 Figure 13 Linear change phase vs frequency22Figure 14 The basic transistor amplifier26 Figure 15 HFA3127 transistor array30 Figure 16 MAV-11SM amplifier31 Figure 17 Suggested PCB layout with MAV-11SM33 Figure 18 Loft box home distributor33 Figure 19 Maxview signal booster35 Figure 20 Antenna used for this project35 Figure 21 Interference between relay signal and main transmitted signal36 Figure 22 ISIS schematic of circuit design37 Figure 23 PCB design according to the datasheet in ARES37 Figure 24 3D view for PCB38 Figure 25 Circuit with HFA3127 amplifier39 Figure 26 MAV-11SM amplifier circuit board40 Figure 27 HFA3127 gain with soldering error41Figure 28 HFA3127 amplifier gain41 Figure 29 One MAV-11SM amplifier gain42 Figure 30 Two MAV-11SM amplifier circuits give more gain42 Figure 31 Three amplifiers together was the maximum gain43 Figure 32 Low quality picture with normal antenna43 Figure 33 Picture with repeater connected antenna44 Figure 34 Rebroadcasting connection44 1. 0 Introduction 1. 1 Background: Digital Video Broadcasting (DVB) is being adopted as the standard for digital television in many countries. The DVB standard offers many advantages over the previous analogue standards and has enabled television to make a major step forwards in terms of its technology.Digital Video Broadcasting, DVB is now one of the success stories of modern broadcasting. The take up has been enormous and it is currently deployed in over 80 countries worldwide, including most of Europe and also within the USA. It offers advantages in terms of far greater efficiency in terms of spectrum usage and power utilisa tion as well as being able to affect considerably more facilities, the prospect of more channels and the ability to work alongside existing analogue services. (Pool, 2002) In these days when there are many ways in hich television can be carried from the â€Å"transmitter†to the â€Å"receiver†no one standard can be optimised for all applications. As a result there are many different forms of the Digital Video Broadcasting, DVB, standards, each designed for a given application. The main forms of DVB are summarised below: DVB Standard| Meaning| Description| DVB-C| Cable| The standard for delivery of video service via cable networks. | DVB-H| Handheld| DVB services to handheld devices, e. g. mobile phones, etc. | DVB-RSC| Return satellite channel| Satellite DVB services with a return channel for interactivity. DVB-S| Satellite services| DVB standard for delivery of television / video from a satellite. | DVB-SH| Satellite handheld| Delivery of DVB services from a satelli te to handheld devices| DVB-S2| Satellite second generation| The second generation of DVB satellite broadcasting. | DVB-T| Terrestrial| The standard for Digital Terrestrial Television Broadcasting. | Digital Video Broadcasting- Terrestrial (DVB-T) : The common perception of digital television these days is of broadcasts emanating from signal towers, bouncing off satellites, and being beamed to home receivers.This is the magic of satellite transmission, and it is reliable as long as the view of those satellites is not obscured. However, this is not the only way in which television signals are transmitted. Another popular method of transmitting signals digital video broadcasting–terrestrial (DVB-T). When broadcasters employ this method, the digital signals do not leave the earth. The signals transmitted using DVB-T do not travel via cable, though; rather, they go from antenna to aerial antenna, from signal blaster to home receiver. Digital signals are routinel y transmitted using terrestrial methods.The transmission method has different names in different parts of the world. DVB-T is the name used in Europe and Australia. North American customers receive these signals using a set of standards approved by the Advanced Television Systems Committee (ATSC). In Japan, it is known as Integrated Services Digital Broadcasting–Terrestrial (IDSB-T). DVB-T broadcasters transmit data using a compressed digital audio-video stream, with the entire process based on the MPEG-2 standard. These transmissions can include all kinds of digital broadcasting, including HDTV and other high-intensity methods.This is a vast improvement over the old analog signals, which required separate streams of transmission. Oddly enough, some DVB-T transmissions take place over analog networks, with the antennas and receivers getting some helpful technological upgrades along the way. (Pool, 2002) 1. 2 Aim of this project The aim of this project is to investigate the design of a repeater for DVB-T system but incorporating a delay between receives and transmits signals to avoid Inter Symbol Interference (ISI). It is useful to use a repeater to boost the signal into areas of weak coverage in any radio wave communication system.However wave interference means the repeater usually requires a frequency shift for analogue modulated signals. For digitally modulated signals it may be possible to use the same frequency. The project will review the basics of current digital systems such as DVB (Broadcast TV) and WLAN – and to identify a suitable choice for a lab experiment. The practical side will be to design and build a repeater incorporating suitable transmission delay. 1. 3 Project objectives 1. Investigate and learn Inter Symbol Interference effect on received signal. 2.Investigate and learn the delay effect on received signal and cause of the delay. 3. Investigate and learn Multipath propagation and Doppler shift of the fre quencies. 4. Investigate and learn about Digital Video Broadcasting (DVB) techniques. 5. Investigate and learn about transmission delay of coaxial cable. 6. Investigate and learn about different type of Amplifier. 7. Designing repeater circuit. 8. Implementing circuit. 9. Testing the circuit. Figure 1System block diagram 1. 3 Project deliverable * System design * Circuit design * Documentation 2. 0 Problem analysis . 1 Repeater Repeaters provide an efficient solution to increase the coverage of the broadcasting networks. In the broadcasting networks, the network operators usually first put high power transmitters at the strategic points to quickly ensure an attractive coverage and then, in a second step, increase their coverage by placing low-power repeaters in the dead spot or shadow areas, such as a tunnel, valley or an indoor area. A repeater is simply a device that receives an analogue signal or a digital signal and regenerates the signal along the next leg of the medium.In DVB- T networks, there are two different kinds of repeaters. They are passive repeaters, which are also called as gap-fillers and active repeaters that are also called as regenerative repeaters. A passive repeater receives and retransmits a DVB-T signal without changing the signalling information bits. The signal is only boosted. An active repeater can demodulate the incoming signal, perform error recovery and then re-modulates the bit stream. The output of the error recovery can even be connected to a local re-multiplexer to enable insertion of local programmes.This means that the entire signal is regenerated. The building blocks of the passive and active repeater configurations are shown in Figure 1. Figure 2 Passive and Active repeater block diagram In a first step, DVB-T broadcasters, as all broadcasters, launch their networks with high power transmitters in strategic point in order to quickly insure an attractive coverage to TV operators and then, in a second step, increase their co verage by placing low power repeaters in shadow area. To repeat a DVB-T signal, two solutions can be used: An analogue repetition: in this case, repeaters use well-known techniques such as down conversion, filtering, up conversion and amplification. The signal is only boosted. * A digital repetition: this new type of repeater uses a professional DVB-T receiver to recover the programme stream (and correct all errors) carried in the RF channel, performs a new modulation followed by an up conversion and amplification. It means that the entire signal is regenerated. 2. 1. 1 Analogue repeaters In case of analogue repetition, the output signal quality cannot exceed the quality of the received signal because the signal is not regenerated.Figure 3 Analog repeater Furthermore, being a passive process, it degrades the signal; the phase noise of the local oscillator involves a degradation of the phase noise of the received signal and creates an inter-modulation. The local oscillator phase nois e adds to the phase noise of the received signal. In these conditions, what are the performances of analogue repetition for Modulation Error Ratio (MER) and Carrier to Noise ratio (C/N)? Of course, performances are linked to the technology but analogue repetition cannot be insured ad infinitum. And, if one link in the analogue repetition chain is weak, all the system is deficient. Trolet, 2002) 2. 1. 2 Digital repeaters In case of a digital repetition, the entire signal is regenerated; it means that repeaters, as transmitters, insure the quality of the broadcasted signal as long as it is able to demodulate it. Figure 4 Digital repeater The output signal quality is independent of the input signal quality: * Phase noise is linked to the local oscillator only, * A weak link, in a digital repetition chain, is erased by the following repeater, * Several digital repeaters can be cascaded without any cumulative degradation.Drawback of Digital repeater The delay inside a digital repeater is taller than the guard interval. So, the signal cannot be repeated on the frequency of the main transmitter: main transmitters and repeaters cannot operate in a Single Frequency Network (SFN) even with 8K carriers and a guard interval of 1/4. (Trolet, 2002) Figure 5 Channel management for digital repeater The delay inside an analogue repeater is lower than the guard interval and allows main transmitters and repeaters to operate in SFN mode. Figure 6 Channel management for analogue repeaterBut, with such technique, overlap between repeater cells and transmitter cell cannot be optimised/adjusted. Analogue repeaters have not the possibility to buffer the signal; they cannot add delay to move the overlap zone. To optimise single frequency network with this technique, two solutions: * Move the repeater that means you have to find new broadcasting site. * Reduce the output power of your repeaters and forbid overlap. So, to build an efficient Single Frequency Network (SFN), Broadcasters ha ve benefits in using transmitters: * Means more freedom for defining the size of the cells Means more freedom for defining the repeater locations Benefits of Digital Repeater * As long as the repeater is able to demodulate the RF channels, signal quality is independent of input signal quality. * Output MER > 33 dB (Trolet, 2002) * In theory, thanks to the forward error correction (FEC) and the output signal quality, digital repeaters can be cascaded ad infinitum. It is an efficient solution to broadcast in valleys. TV viewers and distant repeaters share the broadcasted signal. Figure 7 Broadcast in valley with digital repeaters The demodulation process, down to the programme stream, allows broadcasters to insert a local multiplexor in order to customize the content for a local broadcasting. More and more, local communities claim their local programmes. Digital repeaters offer a flexible solution to the network. * Shadow area can be covered by several repeaters. Repeaters operate tog ether in SFN mode without any external references (10 MHz and 1 PPS) (Trolet, 2002). In their internal memory, digital repeaters can buffer the signal so as to optimise overlaps. 2. 2 Inter symbol interferenceInter-symbol interference (ISI) is an unavoidable consequence of both wired and wireless communication systems. Morse first noticed it on the transatlantic telegraph cables transmitting messages using dots and dashes and it has not gone way since. He handled it by just slowing down the transmission. Amplitude Time Figure 8 101101 transmitted data Figure 8 shows a data sequence, 1,0,1,1,0, which wish to be sent. This sequence is in form of square pulses. Square pulses are nice as an abstraction but in practice they are hard to create and also require far too much bandwidth. Amplitude TimeFigure 9 Received data Figure 9 shows each symbol as it is received. It also shows what the transmission medium creates a tail of energy that lasts much longer than intended. The energy from sym bols 1and 2 goes all the way into symbol 3. Each symbol interferes with one or more of the subsequent symbols. The circled areas show areas of large interference. Amplitude Time Figure 10 Transmitted data vs. Received data Fig. 3 shows the actual signal seen by the receiver. It is the sum of all these distorted symbols. Compared to the transmitted signal, the received signal looks quite indistinct.The receiver does not actually this signal; it sees only the little dots, the value of the amplitude at the timing instant. Symbol 3, this value is approximately half of the transmitted value, which makes this particular symbol is more susceptible to noise and incorrect interpretation and this phenomena is the result of this symbol delay and smearing. This spreading and smearing of symbols such that the energy from one symbol effects the next ones in such a way that the received signal has a higher probability of being interpreted incorrectly is called Inter Symbol Interference or ISI.ISI can be caused by many different reasons. It can be caused by filtering effects from hardware or frequency selective fading, from non-linearity and from charging effects. Very few systems are immune from it and it is nearly always present in wireless communications. Communication system designs for both wired and wireless nearly always need to incorporate some way of controlling it. The main problem is that energy, which is been wishing to confine to one symbol, leaks into others. So one of the simplest things can be done to reduce ISI is to just slowing down the signal.Transmitting the next pulse of information only after allowing the received signal has damped down. The time it takes for the signal to die down is called delay spread, whereas the original time of the pulse is called the symbol time. If delay spread is less than or equal to the symbol time then no ISI will result, otherwise yes. (Charan, 2002) Slowing down the bit rate was the main way ISI was controlled on those ini tial transmission lines. Then faster chips came and allowed to do signal processing controlling ISI and transmission speeds increased accordingly. . 3 Multipath propagation Multipath propagation is caused by multipath receptions of the same signal. in city environment or indoors signal travels along different path from transmitter (Tx) to receiver (Rx). * Signal components received at slightly different times (delay) * These components are combined at Rx * Results as a signal that varies widely in amplitude, phase or polarization 2. 3. 1 Multipath fading When the components add destructively due to phase differences amplitude of the received signal is very small.At the other times the components add constructively the amplitude of received signal is large. This amplitude variations in the received signal called signal fading, are due to the time-variant characteristics of the channel. Relative motion between Tx and Rx (or surrounding objects causing e. g. reflection) causes random f requency modulation. Figure 11 Multipath propagation Each multipath component has different Doppler shift. The Doppler shift can be calculated by using: fd=V? cos? V is the velocity of the terminal ? is the spatial angle between the direction of motion and the wave ? is the wavelengthThe three most important effects of multipath fading and moving scatters are * Rapid changes in signal strength over a small travelled distance or time interval * Random frequency modulation due to varying Doppler shifts on different multipath signals. * Time dispersion (echoes) caused by multipath propagation 2. 4 The TV channels Hertz (Hz) means cycles per second. (Heinrich Hertz was the first to build a radio transmitter and receiver while understanding what he was doing. )  KHz means 1000 Hertz, MHz means 1,000,000 Hertz, and GHz means 1,000,000,000 Hertz The radio frequency spectrum is divided into major bands:Frequency                Wave length (in meters) VLF     very low frequency               3 KHz – 30 KHz              100 Km – 10 Km LF       low frequency           30 KHz – 300 KHz         10 Km – 1 Km MF      medium frequency                 300 KHz – 3 MHz           1 Km – 100 m HF       high frequency 3 MHz – 30 MHz             100 m – 10 m VHF    very high frequency              30 MHz – 300 MHz       10 m – 1 m UHF    ultra high frequency              300 MHz â €“ 3 GHz           1 m – 100 mm SHF    super high frequency            3 GHz – 30 GHz             100 mm – 10 mm EHF    extremely high frequency    30 GHz – 300 GHz         10 mm – 1 mm (Antenna basics, 2008) The UK uses UHF for terrestrial television transmissions, with both PAL-I analogue broadcasts and DVB-T digital broadcasts sharing the band. The following table is a handy channel/frequency conversion table showing the E channel number, PAL-I vision and sound carrier frequencies, and the centre frequency for digital tuning. The frequency plan for the UK involves each channel having an 8MHz bandwidth – the space in the spectrum that each channel is allotted. The PAL-I standard specifies a video bandwidth of 5. 0 MHz and an audio carrier at 6 MHz.The DVB-T tran smissions must fall within this channel plan, resulting in each digital channel also having a bandwidth of 8 MHz. Unlike PAL-I, the digital channel (carrying a multiplexed signal) utilises the entire bandwidth available to it simultaneously, transmitting 2048 carriers (in â€Å"2k mode†). For tuning purposes, a centre frequency is used (Table is included in appendices). (digital spy, 2009) Decibels Decibels (dB) are commonly used to describe gain or loss in circuits. The number of decibels is found from: Gain in dB = 10*log(gain factor)       or (Antenna basics, 2008) In some situations this is more complicated than using gain or loss factors. But in many situations, decibels are simpler.For example, suppose 10 feet of cable loses 1 dB of signal. To figure the loss in a longer cable, just add 1 dB for every 10 feet. In general, decibels let add or subtract instead of multiply or divide. Noise Whether a signal is receivable is determined by the signal t o noise ratio (S/N). For TVs there are two main sources of noise: 1. Atmosphere noise. There are many types of sources for this noise. A light switch creates a radio wave every time it opens or closes. Motors in some appliances produce nasty RF (radio frequency) noise. 2. Receiver noise. Most of this noise comes from the first transistor the antenna is attached to. Some receivers are quieter than others. 2. Transmission cable Twin lead (ribbon cable) used to be common for TV antennas. It has its advantages. But due to its unpredictability when positioned near metal or dielectric objects, it has fallen out of favour. Coaxial cable is recommended. It is fully shielded and not affected by nearby objects. Transmission cable has a feature called its characteristic impedance, which for TV coax should always be 75 ohms. Although rated in ohms, this has nothing to do with resistance. A resistor converts electric energy into heat. The â€Å"75 ohms†of a coaxial cable does not cause heat. Where it comes from is mathematically complicated and beyond our scope here.But coax also has ordinary resistance (mostly in the center conductor) and thus loses some of the signal, converting it into heat. The amount of this dissipation (loss) depends on the frequency as well as the cable length. Type:        Centre conductor:    Cable diameter:     RG-59      20-23 gauge             0. 242 inches     RG-6         18 gauge                   0. 265 inches     RG-11      14 gauge                   0. 405 inches Figure 12 Cable loss in dB  (Antenna basics, 2008) The above chart is only approximate. There are many cable manufacturers for each type and there is no enforcement of stand ards. If the mast-mounted amplifier gain exceeds the cable loss then it shouldn’t matter what cable you use.But there are two problems with this: * Some cable has incomplete shielding. This is most common for RG-59, another reason to avoid it. * When the cable run is longer than 200 feet, the low-numbered channels can become too strong relative to the high-numbered channels. In this case, RG-11 or an ultra-low-loss RG-6 is recommended. (These alternatives are expensive. )  Alternatively, frequency compensated amplifiers will work. 2. 6 Signal Amplifiers There are two types of signal amplifiers: Preamplifiers  (Mast-mounted amplifiers)  –  These should be mounted as close to the antenna as possible. Usually the amplifier comes in two parts: 1. The amplifier.This is an outdoor unit that is normally bolted to the antenna mast. It must have a very low noise figure, and enough gain to overcome the cable loss and the receiver’s noise figure. 2. The power module (power injector). This is an indoor unit that commonly lies on the floor behind the TV. It is inserted into the antenna cable between the amplifier and the TV. This module injects some power, usually DC, into the coaxial cable where the amplifier can use it. The power injector is the amplifier’s power supply. Distribution amplifiers  –  These are simple signal boosters. They are often necessary when an antenna drives multiple TVs or when the antenna cable is longer than 150 feet.Distribution amplifiers don’t need to have a low noise figure, but they need to be able to handle large signals without overloading. Commonly, distribution amplifiers have multiple outputs. (Unused outputs usually do not need to be terminated. ) Never feed an amplifier output directly into another amplifier. There should always be a long cable between the preamplifier and the distribution amplifier. Placing the two amplifiers close together can cause overloa d and/or oscillation. A mast-mounted amplifier’s most important characteristic is its noise level, usually specified by the noise figure. But many manufacturers don’t take this number seriously. If it is given at all, it is often wrong. If all makers don’t do them right then comparison-shopping is not possible.The author is inclined to rate amplifiers for their noise figures as follows:       0. 5 dB superb (anything better runs into thermal atmospheric noise)       2. 0 dB excellent 4. 0 dB fair 6. 0 dB poor 10 dB awful 2. 7 Transmission delay (Coaxial cable) Transmission lines are described by their two most important characteristics: the characteristic impedance Zo and the delay. For instance, a â€Å"short†(say 0. 01 wavelength) piece of coaxial cable such RG-58U has been taken and measured its capacitance with the other end open. A one foot length yields more or less 31. 2 pF. The inductance also has been measured with the other end shorted. It yields 76. 8 nH. The impedance may now be computed as: Zo=LC Zo=76. ? 10-931. 2? 10-12=49. 6 ohms Here L and C are measured for the same length. The delay may also be computed: Delay= L? C Delay= 76. 8? 10-9? 31. 2? 10-12=1. 55 nSec For an ideal line, the delay increases linearly with its length, while its impedance remains constant. After that it has been computed the velocity in foot per second: V=lendelay V=11. 55? 10-9=6. 46? 108 foot per second or meters/second 8 10*966. 1 This is less than the speed of light. The ratio of the above speed to the speed of light gives the velocity factor Vf: Vf=1. 966? 1082. 998? 108=0. 666 or 66. % of the speed of light As mentioned earlier, the delay increases linearly with the line length. For a given length, the phase difference between the input and output will increase with the frequency: ? =2? f? delay Here the phase ? is in radians and the frequency f is Hertz. Converting the phase from ra dians to degrees requires multiplying by: 3602? In this case if frequency is 900 MHz so phase delay will be ?deg=f? 360? delay=900? 106? 360? 1. 55? 10-9? 502. 2 This length that gives 90 degrees of phase shift is also known as a quarter wavelength. Figure 13 Linear change phase vs frequency Figure-13 An ideal transmission line gives a linear change of phase versus frequency.The distributed inductance and capacitance are the basic transmission line parameters. From these, it can be calculated the line impedance, the delay in terms of time and phase, the speed of propagation and the velocity factor. The inductive component has an additional component at the lower frequencies which slows the signal somewhat. This occurs around 100 KHz for small coax and lower for larger cables. For frequencies above 1 MHz, the dielectric constant of the cable is probably responsible for the decrease in the delay. Measuring the delay of cables can reveal some â€Å"hidden†properties that could make it unsuitable for some applications, such as carrying wideband data. (Audet, 2001) 3. 0 Possible solutionThe main component of a repeater is amplifier. There are many types of amplifier can be used for this job. RF amplifiers are electronic devices that accept a varying input signal and produce an output signal that varies in the same way as the input, but that has larger amplitude. RF amplifiers generate a completely new output signal based on the input, which may be voltage, current, or another type of signal. Usually, the input and output signals are of the same type; however, separate circuits are used. The input circuit applies varying resistance to an output circuit generated by the power supply, which smoothes the current to generate an even, uninterrupted signal.Depending on load of the output circuit, one or more RF pre-amplifiers may boost the signal and send the stronger output to a RF power amplifier (PA). Other types of RF amplifiers include low noise, pulse, bi-directional, multi-carrier, buffer, and limiting amplifiers. Detector log video amplifiers (DLVAs) are used to amplify or measure signals with a wide dynamic range and wide broadband. Successive detection log video amplifiers (SDLVAs) are log amplifiers that can operate over a wider dynamic range than DLVAs, while extended range detector log video amplifiers (ERDLVAs) are DLVAs that can operate with a wider operating frequency. (Global Spec, 2008) * Military / Defense * Mobile / Wireless Systems * Plasma / Electron Laser * RF Induction Heating * Radar SystemsAmplifier Type: Applications: * Low Noise Amplifier * Power Amplifier * Bi-directional Amplifier * Multi-carrier Amplifier * Multiplier (RF amplifier, 2008) 3. 1 RF amplifier Selecting RF amplifiers requires an analysis of several performance specifications. Operating frequency is the frequency range for which RF amplifiers meet all guaranteed specifications. Design gain, the ratio of the output to the i nput power, is normally expressed in decibels (dB), or Gdb = 10 * log (Po/Pi) Output power is the signal power at the output of the amplifier under specified conditions such as temperature, load, voltage standing wave ratio (VSWR), and supply voltage.Gain flatness indicates the degree of the gain variation over its range of operating wavelengths. Secondary performance specifications to consider include noise figure (NF), input VSWR, output VSWR, and monolithic microwave integrated circuit (MMIC) technology. The noise figure, a measure of the amount of noise added to the signal during normal operation, is the ratio of the signal-to-noise ratio at the input of the component and the signal-to-noise ratio measured at the output. The NF value sets the lower limit of the dynamic range of the amplifier. Input VSWR and output VSWR are unit-less ratios ranging from 1 to infinity that express the amount of reflected energy. Global Spec, 2008) There are several physical and electrical specifications to consider when selecting RF amplifiers. Physical specifications include package type and connector type. Package types include surface mount technology (SMT), flat pack, and through hole technology (THT). RF amplifiers may also be connector zed or use waveguide assemblies. Connector types include BNC, MCX, Mini UHF, MMCX, SMA, SMB, SMP, TNC, Type F, Type N, UHF, 1. 6 / 5. 6, and 7/16. Important electrical characteristics include nominal operating voltage and nominal impedance. Operating temperature is an important environmental parameter to consider. (Global Spec, 2008) 3. 1. 1 The Transistor AmplifierIn the preceding section explains the internal workings of the transistor and will introduce new terms, such as emitter, base, and collector. Here it discusses the overall operation of transistor amplifier. To understand the overall operation of the transistor amplifier, it must have to only consider the current in and out of the transistor and through the various components in the circuit. Therefore, from this point on, only the schematic symbol for the transistor will be used in the illustrations, and rather than thinking about majority and minority carriers that mean it will be only emitter, base and collector current. Before going into the basic transistor amplifier, there are two terms it should be familiar with: AMPLIFICATION and AMPLIFIER.Amplification is the process of increasing the strength of a SIGNAL. A signal is just a general term used to refer to any particular current, voltage, or power in a circuit. An amplifier is the device that provides amplification (the increase in current, voltage, or power of a signal) without appreciably altering the original signal. Transistors are frequently used as amplifiers. Some transistor circuits are CURRENT amplifiers, with a small load resistance; other circuits are designed for VOLTAGE amplification and have a high load resistance; others amplify POWER. By inserting one or more resistors in a circuit, different methods of biasing may be achieved and the emitter-base battery eliminated.In addition to eliminating the battery, some of these biasing methods compensate for slight variations in transistor characteristics and changes in transistor conduction resulting from temperature irregularities. Notice in figure 2-12 that the emitter-base battery has been eliminated and the bias resistor RB has been inserted between the collector and the base. Resistor RB provides the necessary forward bias for the emitter-base junction. Current flows in the emitter-base bias circuit from ground to the emitter, out the base lead, and through RB to VCC. Since the current in the base circuit is very small (a few hundred microamperes) and the forward resistance of the transistor is low, only a few tenths of a volt of positive bias will be felt on the base of the transistor.However, this is enough voltage on the base, along with ground on the emitter and the large positive voltage on the collector, to properly bias the transistor. (Intregrated Publishing, 2002) Figure 14 The basic transistor amplifier With Q1 properly biased, direct current flows continuously, with or without an input signal, throughout the entire circuit. The direct current flowing through the circuit develops more than just base bias; it also develops the collector voltage (VC) as it flows through Q1 and RL. Notice the collector voltage on the output graph. Since it is present in the circuit without an input signal, the output signal starts at the VC level and either increases or decreases.These dc voltages and currents that exist in the circuit before the application of a signal are known as quiescent voltages and currents (the quiescent state of the circuit). Resistor RL, the collector load resistor, is placed in the circuit to keep the full effect of the collector supply voltage off the collector. This permits the collector voltage (VC) to change with an input signal , which in turn allows the transistor to amplify voltage. Without RL in the circuit, the voltage on the collector would always be equal to VCC. The coupling capacitor (CC) is another new addition to the transistor circuit. It is used to pass the ac input signal and block the dc voltage from the preceding circuit. This prevents dc in the circuitry on the left of the coupling capacitor from affecting the bias on Q1.The coupling capacitor also blocks the bias of Q1 from reaching the input signal source. The input to the amplifier is a sine wave that varies a few millivolts above and below zero. It is introduced into the circuit by the coupling capacitor and is applied between the base and emitter. As the input signal goes positive, the voltage across the emitter-base junction becomes more positive. This in effect increases forward bias, which causes base current to increase at the same rate as that of the input sine wave. Emitter and collector currents also increase but much more th an the base current. With an increase in collector current, more voltage is developed across R L.Since the voltage across RL and the voltage across Q1 (collector to emitter) must add up to VCC, an increase in voltage across RL results in an equal decrease in voltage across Q1. Therefore, the output voltage from the amplifier, taken at the collector of Q1 with respect to the emitter, is a negative alternation of voltage that is larger than the input, but has the same sine wave characteristics. During the negative alternation of the input, the input signal opposes the forward bias. This action decreases base current, which results in a decrease in both emitter and collector currents. The decrease in current through RL decreases its voltage drop and causes the voltage across the transistor to rise along with the output voltage.Therefore, the output for the negative alternation of the input is a positive alternation of voltage that is larger than the input but has the same sine wave characteristics. By examining both input and output signals for one complete alternation of the input, we can see that the output of the amplifier is an exact reproduction of the input except for the reversal in polarity and the increased amplitude (a few millivolts as compared to a few volts). The PNP version of this amplifier is shown in the upper part of the figure. The primary difference between the NPN and PNP amplifier is the polarity of the source voltage. With a negative VCC, the PNP base voltage is slightly negative with respect to ground, which provides the necessary forward bias condition between the emitter and base.When the PNP input signal goes positive, it opposes the forward bias of the transistor. This action cancels some of the negative voltage across the emitter-base junction, which reduces the current through the transistor. Therefore, the voltage across the load resistor decreases, and the voltage across the transisto r increases. Since VCC is negative, the voltage on the collector (VC) goes in a negative direction (as shown on the output graph) toward -VCC (for example, from -5 volts to -7 volts). Thus, the output is a negative alternation of voltage that varies at the same rate as the sine wave input, but it is opposite in polarity and has a much larger amplitude.During the negative alternation of the input signal, the transistor current increases because the input voltage aids the forward bias. Therefore, the voltage across RL increases, and consequently, the voltage across the transistor decreases or goes in a positive direction (for example: from -5 volts to -3 volts). This action results in a positive output voltage, which has the same characteristics as the input except that it has been amplified and the polarity is reversed. (Intregrated Publishing, 2002) 3. 1. 2 Ultra High Frequency Transistor Array (HFA) The HFA3046, HFA3096, HFA3127 and the HFA3128 are Ultra High Frequency Tra nsistor Arrays that are fabricated from Intersil Corporation’s complementary bipolar UHF-1 process.Each array consists of five dielectrically isolated transistors on a common monolithic substrate. The NPN transistors exhibit a fT of 8GHz while the PNP transistors provide a fT of 5. 5GHz. Both types exhibit low noise (3. 5dB), making them ideal for high frequency amplifier and mixer applications. (HFA3127, 2003) The HFA3046 and HFA3127 are all NPN arrays while the HFA3128 has all PNP transistors. The HFA3096 is an NPN-PNP combination. Access is provided to each of the terminals for the individual transistors for maximum application flexibility. Monolithic construction of these transistor arrays provides close electrical and thermal matching of the five transistors. Features * NPN Transistor (fT) . . . . . . . . . . . . . . . . . . . . . . . . 8GHz * NPN Current Gain (hFE). . . . . . . . . . . . . . . . . . . . . . . . 130 * NPN Early Voltage (VA) . . . . . . . . . . . . . . . . . . . . . . . 50V * PNP Transistor (fT). . . . . . . . . . . . . . . . . . . . . . . . . 5. 5GHz * PNP Current Gain (hFE). . . . . . . . . . . . . . . . . . . . . . . . . 60 * PNP Early Voltage (VA) . . . . . . . . . . . . . . . . . . . . . . . .20V * Noise Figure (50? ) at 1. 0GHz . . . . . . . . . . . . . . . . . 3. 5dB * Collector to Collector Leakage . . . . . . . . . . . . . . . . . .30 dB) and this transistor amplifier gain was not enough for rebroadcasting signal, this project select another amplifier MAV-11SM from supervisor suggestion. One MAV-11SM amplifier gives around 10dB gain what has been shown in testing section. At last two MAV-11SM amplifiers and one HFA3127 has been used to get more than 30dB gain. It has been tested in network scalar analyzer. For field test, a TV card, three TV aerials have been used. The amplifier circuit has been connected with one aerial. It was working very well when it was directly connected with TV card. That it can be said that the repe ater was amplifying signal.But when another aerial with long transmission line was connected with amplifier and tried to rebroadcast the signal with 5v 1A power supply, TV picture quality was not improving expectedly. Digital repetition is an innovative concept, which helps to increase the DVB-T coverage while maintaining the highest quality and providing a greater flexibility. In spite of failure, this project was a high level platform to learn about signal and signalling. Future work: As this project is unsuccessful at that certain point, this project will try to solve the rebroadcasting problem. And the transistor array will be a great option to amplify signal if all five transistors are been used. From HFA3127, it is possible to get min of 120 dB gain if it is soldered perfectly. Works CitedAntenna basics. (2008, October 12). Retrieved May 5, 2011, from http://www. hdtvprimer. com/ANTENNAS/basics. html. Audet, J. (2001). Coaxial Cable Delay. Charan, L. (2002). Inter symbos Inter ferance (ISI) and Raised Cosine filters. Retrieved December 5, 2010, from http://www. complextoreal. com/chapters/isi. pdf. Datasheet. (2005, December 21). Retrieved February 20, 2011, from http://www. intersil. com/data/fn/fn3076. pdf. digital spy. (2009). Retrieved April 10, 2011, from http://www. digitalspy. co. uk/digitaltv/information/a12613/uhf-channel-and-frequency-guide. html. Global Spec. (2008). Retrieved April 10, 2011, from http://www. globalspec. om/learnmore/telecommunications_networking/rf_microwave_wireless_components/rf_amplifiers. HFA3127. (2003). Retrieved January 18, 2011, from http://www. intersil. com/products/deviceinfo. asp? pn=HFA3127. Intregrated Publishing. (n. d. ). Retrieved April 4, 2011, from http://www. tpub. com/neets/book7/25c. htm. Monolithic Amplifier. (2002). Retrieved January 14, 2011, from http://www. minicircuits. com/pdfs/MAV-11SM+. pdf. Pool, I. (2002). Digital Video Broadcasting. Retrieved April 13, 2011, from http://www. radio-electronics. com/info/broadcast/digital-video-broadcasting/what-is-dvb-tutorial. php. Power Amplifier design. (1998). RF transmitting transistor and power ampli? er fundamentals . RF amplifier. (2008).Retrieved April 10, 2011, from http://www. globalspec. com/learnmore/telecommunications_networking/rf_microwave_wireless_components/rf_amplifiers. sub-TV. (2006, October 13). Retrieved April 20, 2011, from http://www. sub-tv. co. uk/antennatheory. asp. Trolet, C. (2002). SPOT: filling gaps in DVB-T networks with digital repeaters. Presented by Gerard Faria, Scientific Director, Harris Broadcast Europe at BroadcastAsia2002 International Conference, Available at: http://www. broadcast. harris. com. Gantt chart APPENDICES Frequency Allocation for DVB-T in UK Band IV Channel| PAL-I Vision (MHz)| PAL-I Sound (MHz)| Centre (MHz)| 21| 471. 25| 477. 25| 474| 22| 479. 25| 485. 25| 482| 3| 487. 25| 493. 25| 490| 24| 495. 25| 501. 25| 498| 25| 503. 25| 509. 25| 506| 26| 511. 25| 517. 25| 514| 27| 519. 25| 52 5. 25| 522| 28| 527. 25| 533. 25| 530| 29| 535. 25| 541. 25| 538| 30| 543. 25| 549. 25| 546| 31| 551. 25| 557. 25| 554| 32| 559. 25| 565. 25| 562| 33| 567. 25| 573. 25| 570| 34| 575. 25| 581. 25| 578| 35| 583. 25| 589. 25| 586| 36| 591. 25| 597. 25| 594| 37| 599. 25| 605. 25| 602| 38| 607. 25| 613. 25| 610| Band V Channel| PAL-I Vision (MHz)| PAL-I Sound (MHz)| Centre (MHz)| 39| 615. 25| 621. 25| 618| 40| 623. 25| 629. 25| 626| 41| 631. 25| 637. 25| 634| 42| 639. 25| 645. 25| 642| 43| 647. 25| 653. 25| 650| 44| 655. 25| 661. 5| 658| 45| 663. 25| 669. 25| 666| 46| 671. 25| 677. 25| 674| 47| 679. 25| 685. 25| 682| 48| 687. 25| 693. 25| 690| 49| 695. 25| 701. 25| 698| 50| 703. 25| 709. 25| 706| 51| 711. 25| 717. 25| 714| 52| 719. 25| 725. 25| 722| 53| 727. 25| 733. 25| 730| 54| 735. 25| 741. 25| 738| 55| 743. 25| 749. 25| 746| 56| 751. 25| 757. 25| 754| 57| 759. 25| 765. 25| 762| 58| 767. 25| 773. 25| 770| 59| 775. 25| 781. 25| 778| 60| 783. 25| 789. 25| 786| 61| 791. 25| 797. 25| 794| 62| 799. 25| 805. 25| 802| 63| 807. 25| 813. 25| 810| 64| 815. 25| 821. 25| 818| 65| 823. 25| 829. 25| 826| 66| 831. 25| 837. 25| 834| 67| 839. 25| 845. 25| 842| 68| 847. 25| 853. 25| 850|
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