Respiratory therapy Essay Example | Topics and Well Written Essays - 500 words

Respiratory treatment - Essay Example He didn't see a specialist in spite of the fact that he was encouraged to. Exactly when his fever arrived at 38.3 C (101F) and he was encountering brevity of breath he drove himself to the medical clinic. O: Patient was all around sustained, and in respiratory misery n 2l/min oxygen by nasal cannula. His pulse was 165/90, pulse of 120 bpm, respiratory pace of 33/min and oral temperature of 39.5 C (105F). He showed a regular solid hacky and profitable hack of white and yellow sputum. His skin seemed pale and soggy. At the way to express the 99 expression the expanded material and vocal fremitus were seen over the correct lower lung alongside bronchial sounds in a similar locale. His oxygen immersion was 87% and his blood vessel blood gases were as per the following: pH 7.56, PaCO2 24 mmHg, HCO3 - 24 mmol/L, PAo2-56mmHg. His chest X-beam shows a correct flap penetrated with pneumonia, air bronchograms, and alveolar solidification. His white platelet tally was 21,000mm^3. S: The specialist playing out the rounds, after 6 hours, saw that the patient grumbled that his primary care physician is excessively youthful and that he feels more regrettable when he went to the emergency clinic, in spite of the fact that right now his vitals were better O: hypertension at 135/85, hr=90bpm, and resp, rate=19/min; oral temperature was 37.3C or 99F.; he likewise had solid inefficient hack; chest beam showed a halfway goals of the pneumonia, his bronchial breath sounds were perceptible and his SPO2 and ABGs values improved

Using “Too much punch for judy” as a stimulus

In the second exercise we needed to carry on ‘A night on the town’ as still pictures, we did this in a gathering of four (myself, Luke, Reece and lee). Our upgrade for this undertaking was our own perception from perusing the content. In the initial two scenes we had a part stage, demonstrating two men and two ladies preparing for their night out, in doing so we needed to make juxtaposition; so the crowd can plainly separate between the two gatherings of individuals in the still picture. In the third scene we needed to show a despite everything picture of the two men viewing the two ladies in the bar we (me and Reece) needed to upgrade our outward appearances and non-verbal communication to appear pulled in to the ladies (Luke and Lee). What we did to show that we was keen on the two young ladies was have our view straightforwardly on them, and our bodies must be very ‘masculine’ and outward appearances were curious, we made this conceivable by causing a commotion and having wide eyes, and our heads were reclined at a point, to show that we are ‘checking them out’. Lee and Luke needed to close themselves from the crowd, and make them face the floor, to show bashfulness. We did this to show a regular night out in a bar, it was a show. Towards the finish of the exercise we needed to form the still pictures into a pretend, utilizing visit up lines and other explorative methodologies. In the main scene we had the two gatherings preparing for their night out, simultaneously, yet this time we included development, and discourse. Myself and Reece playing the two men, was from east London, so we had a run of the mill cockney complement , and moderate and overwhelming development, to make a feeling of quality. To make the two ladies to begin acting, we denoted the second by utilizing the line ‘come on mate, dislike we’re ’gonna’ crash. After that line was said that was the sign for Luke and Lee to begin their presentation, they were two ordinary ladies from Essex; with their pretend they upgraded the ladies by having female developments and doing commonplace motions for instance putting on make-up and asking ‘if this outfit looks pleasant? The following scene included us in the bar, we gazed with the men entering the bar before the ladies, and they’ve effectively settled with a beverage. With our characterisation we had made two common men searching for ladies to visit up to in a bar, we had a quiet and smooth tone to our voices to mean this. When the two ladies entered the bar, we solidified with a despite everything picture that we utilized in the main exercise, to proceed with the presentation I claimed to murmur in to Reece’s ear ‘I’m having the one on the left. We had a spilt stage where the two gatherings talked between one another, while the other gathering emulated out of sight. This was done so the crowds could comprehend what the men and women’s aims were. Each gathering discussed their affections for the individual they need to ‘chat-up with, we did this draw in the crowd as we are uncovering our motivations in this exhibition. To end our exhibition Reece approached Lee and utilized a ‘cheesy visit up line’ so we can polish off with a touch of satire; the line was ‘Hey angel, I’ve got the pencil; and you’ve got the sharpener! Soon after that line we went straight into a despite everything picture, to show the stun on the entirety of our appearances as though to state, that was the most exceedingly awful visit up line utilized. In another exercise we needed to watch a short ad about beverage driving, and the consequences for liquor on individuals. We needed to make a short mindfulness advert that shows the impacts of alcoholic driving, and an approach to quit driving while inebriated with liquor. Our gathering comprised of, me (driver), Brandon (traveler), Binte (traveler) and Tyrell (traveler). We concocted a fundamental blueprint for a presentation. The story was the four of us went on a run of the mill ‘night out’ and become inebriated and chosen to commute home, when I put the key in the start we solidified, representing that I was having a dream, yet was ignorant of it. We at that point utilized authenticity to emulate us driving along in a key, by doing standard conventions, or missing them and afterward acknowledging what occurred, we did to show the crowd that drinking can more slow your response and thinking process . At that point unexpectedly Brandon reports that he has another beverage in his pocket, this causes a fight in the vehicle as we battle for the beverage, at that point Tyrell, who is the front seat traveler , stretches around and kicks the controlling wheel, making the vehicle roam and crash into a tree, to depict the accident we tossed our bodies in various ways as though we got tossed out, we did this as it was naturalism, as it’s common to get toss about in auto collision and go a totally extraordinary way . At that point we re-wound the entire excursion, including the accident, this was us utilizing physical theater and cross-cutting, we did this to improve and connect with the crowd as it would be considerably more fascinating to watch rather than essentially simply decreasing to the firs scene. At the point when we returned to the primary scene when I put the key in the start we halted, and afterward we cut out all solid and I had a fast idea track, while the others were emulating out of sight, I discussed my vision and what is going to occur, we came back to the exhibition by Tyrell hitting me and saying ‘hurry up lets go’ as he did the first run through, to show this was this present reality now. I unexpectedly said ‘No! We’re not driving’ then out of nowhere we imagined another vehicle hitting a tree, which would have been us, this was the anti-agents from driving.

Spring 2017 Transfer Reviews - UGA Undergraduate Admissions

Spring 2017 Transfer Reviews - UGA Undergraduate Admissions Spring 2017 Transfer Reviews Today, our office started reviewing Spring 2017 transfer applications. This is earlier than I expected, but we are way ahead of the timelines we have predicted for Fall transfers files and final HS transcripts for freshmen. The 8/15 application deadline for spring has not passed and we are still receiving applications and documents, so we cannot say how long it will take us to finish or guess when you will hear a decision. If you applied for the spring term, please be sure to check your myStatus to see if we have your most up-to-date transcript(s). If you were enrolled in coursework this summer and have not sent a transcript with your summer grades, you should have one sent as soon as possible. To be complete and ready to review, we must have a transcript from each college/university you havepreviouslyattended. If you are attending a new college starting in the Fall 2016 semester, we do not need a transcript, as there will not be any grades on the transcript. If you are admitted, we will need a transcript when fall term is done, though, as we will need to post these grades. Transfer decisions are made on a daily basis Monday through Friday, and it varies on how many decisions we can make in a day due to the complexity of some transfer files. The myStatus page is updated in the early a.m. every business morning, and decisions are posted on the myStatus page and are mailed to transfer applicants.We generally try to review files based on when a file is complete (earliest to latest), but this is not an exact science due to complexities within the transfer process. During the first few weeks of August, decisions might be a bit slower than normal due to also having to input summer work for incoming/returning students, but that should slow down by the start of class (8/11). We will be reviewing Spring Freshmen applicants sometime in mid-late September after the deadline has passed and all files are ready for review. Go Dawgs!

British Invasion Free Essay Example, 1000 words

The British Invasion The British Invasion is a term that is used to describe the flow of rock-n-roll performers from Great Britain to the USA, who became very popular there and started a great wave of popularization of the rock music. The peak of the British Invasion was in 1964-1966. It is interesting that the roots of this phenomenon are grounded in the USA with the explosion of the rock and roll music in America in 1955. Inspired and amazed by the new style of music and the success of the rock singers and bands, such as Elvis Presley, Bill Haley, the Comets and others, British teenagers started forming their own bands trying to copy their American idols. They did not only copy their music style, but their rebellious images that were close to British youth. Thanks to that a few successful British artists appeared, namely The Shadows and Cliff Richard, but their popularity was nothing close to that of the American musicians, and therefore their influence on the American music charts was limited. In 1962 the single Telstar by the British band The Tornadoes became number one in the USA. We will write a custom essay sample on British Invasion or any topic specifically for you Only $17.96 $11.86/pageorder now This event marked the initial stage of the British Invasion. But the real start of this great wave of music was in December 1963, when the song I Want to Hold Your Hand by The Beatles appeared on American radio stations and became extremely popular. On February 9th 1964, the Beatles performed live on The Ed Sullivan Show and from that day on Beatlemania swept the United States. â€Å"This appearance was a remarkable social and cultural milestone of the 1960s, and marked the dramatic start of the British Invasion† (The British Invasion) The special flavor that the British musicians added to the initially American sound, made this music very popular. At it is known, there were two schools in the British invasion. The groups representing the first school were called â€Å"skiffle† bands. Skiffle is a modern folk-country-blues. â€Å"The genesis of skiffle lay in the "trad-jazz" tradition of music that had itself sprung from New Orleans "Dixieland" jazz† (Fontenot) The instruments that these bands used were simple and inexpensive, mostly homemade – â€Å"tea chests fashioned into standup basses, guitars made from cigar boxes, washboards for percussion, and an occasional acoustic guitar or piano† (Fontenot) The typical representatives of the style were the Ken Colyer Skiffle Band and Lonnie Donegan, who established skiffle as the musical phenomenon. Even though skiffle music is considered the one to be played by simple folks, who could not afford expensive instruments, such great rock groups as The Beatles and The Kinks started out their careers and road to popularity as the skiffle bands.

Using High School Graduation Essay Topics

Using High School Graduation Essay Topics High school is the ideal time to practice delivering a persuasive speech, and therefore don't miss the chance to learn to deliver a persuasive speech. In case the job of delivering a graduation speech has fallen on you, there are a few things to remember. Each region of the procedure for creating and delivering great graduation speeches has lots of distinctions and should you have enough time you may spend it improving your speech through various practices. To produce and deliver a graduation speech isn't really any different. Finding High School Graduation Essay Topics on the Web Not many people wind up paying the whole cost printed on college sites. Buying a graduation invitation set from the school is simple, but there are a lot of disadvantages to doing so. So for instance, you could be giving a presentation about the market for coffee in a particular city. There are many ways to earn a cash gift more personal and distinctive. Choosing Good High School Graduation Essay Topics Sure, today it appears that getting your hands on any sort of information is straightforward. Take what you've learned throughout the previous 12 decades and set it to good use. If you're following several directions, and you've got a great emergency kit that's ideal for college living, then whether you're a college student or whether you're the parent of one, you are going to know that everything was accounted for and everything is going to be taken care of. Your college student will require a flashlight and a great battery powered radio with a reversal of batteries also. You might choose to pursue a career right after graduation or maybe you opt to enroll directly into college. If your student is interested in attending colleges more than a couple of hours from your house, you are going to want to think of a game plan to see college campuses. Many students spend an excessive amount of money on textbooks annually. Always ma ke certain that your college student knows where they ought to meet you. High School Graduation Essay Topics - the Story Perhaps, you will find precisely what you need in different categories. To choose which subject you're likely to discuss, it's crucial to see the complete collection of good persuasive speech topics from the special area of study. When you have chosen a topic, conduct research. For this reason, you might have to look for good topics for high school research papers on the net. Life, Death and High School Graduation Essay Topics You will be able to keep in mind, and so will they. The graduation party will require the correct plan which makes all the correct moves at the perfect moment. Every day marks the start of the next day of your life but there are particular days that represent big milestones. The Benefits of High School Graduation Essay Topics What you say in those High School graduation speeches ought to be something they'll remember whether they g et Olympic swimmers or simply splash around in the neighborhood pool of life. Graduation is a process which goes on until the previous day of your life. An invitation might include word of mouth, email, or an official invitation. Along with price, the graduation invitation sets offered by the majority of schools aren't unique. You're able to select any country that's at war with a different one, addressing the citizens to hate citizens from another nation. In the future, it opens lots of opportunities for folks to be successful. To begin with, high schools are places that help to acquire people ready to operate in the adult world. All in all, they are definitely a vital institution that young people need to attend in order to get the basic book skills and society type of skills so that they can cope with the adult world, do well in their prospective jobs and do well when interacting with other people. Up in Arms About High School Graduation Essay Topics? High school essay writing is a typical classroom activity and is also part of several normal examinations. You have to demonstrate facts employing colorful language instead of merely telling. You are able to use narrative essay examples high school to find out more. P.S. Keep in mind you're able to contact online academic writers to aid in topic selection along with writing the entire paper from A to Z. Ultimately, if you are going to write and essay but have very little knowledge or interest in the topic, remember there are lots of custom essay writers which will gladly do the task for you. With endless possibilities and a deadline just around the corner, it's no surprise that you have turned to Google for a tiny inspiration and suggestions on ways to get the ideal paper topic. Another good idea is to receive some totally free essay examples of different sorts and on various subjects to find a general idea of the way in which a prosperous debatable paper looks. The last write-up needs to be concise with firm language. The Upside to High School Graduation Essay Topics Think of one privilege which you would love to have that you don't have now. Certainly, the admissions essay has become the most challenging portion of the graduate school application. Also, keep in mind that you'll have to offer some factual evidence for your opinion (after all, any academic paper needs to be supp orted by academically recognized sources), thus don't go for subjects which are purely opinionated and don't have any possibility of justification. Within the body section, you must give supporting arguments for each point which you make. Indeed even the simple fact that you may have to compete against other graduation parties could just offer you a few concerns. Write an essay to convince your principal your idea is one that ought to be adopted. Very often it becomes tough to choose a single topic either due to the many ideas in the student's head, or due to their complete absence. Want to Know More About High School Graduation Essay Topics? Going away to college can be a great time for somebody to mature and start their adult life, but in addition, it can provide a person the chance to go downhill in life decisions. It's OK to wonder but, I also think it's important to realize our future isn't just something which happens to us. The first thing is vital in getting you started is choosing the proper topic for you as well as the audience. Think of yourself and a few of your pals.

Design a Repeater for Digital Rf Signal Free Essays

string(91) " improvement over the old analog signals, which required separate streams of transmission\." 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. We will write a custom essay sample on Design a Repeater for Digital Rf Signal or any similar topic only for you Order Now 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 Analogue 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 Digital 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 frequency22 Figure 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 error41 Figure 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 utilisation 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| Han dheld| 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 satellite 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 routinely 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. You read "Design a Repeater for Digital Rf Signal" in category "Essay examples" 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 frequencies. 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 coverage 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 regenerat ed. 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 noise 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 t he 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 repeater But, 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 have 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 together 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 interference Inter-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 Time Figure 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 symbols 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 initial 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 compone nts 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 frequency 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 wavelength The 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. )  Ã‚  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  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Wavelength  (in meters) VLF  Ã‚  Ã‚  Ã‚  Ã‚  very low frequency  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  3 KHz – 30 KHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   100 Km – 10 Km LF  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  low frequency  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   30 KHz – 300 KHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚      10 Km – 1 Km MF  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  medium frequency  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  300 KHz – 3 MHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   1 Km – 100 m HF  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  high frequency 3 MHz – 30 MHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   100 m – 10 m VHF  Ã‚  Ã‚  Ã‚  very high frequency  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  30 MHz – 300 MHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   10 m – 1 m UHF  Ã‚  Ã‚  Ã‚  ultra high frequency  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  300 MHz – 3 GHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   1 m – 100 mm SHF  Ã‚  Ã‚  Ã‚  super high frequency  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   3 GHz – 30 GHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚      100 mm – 10 mm EHF  Ã‚  Ã‚  Ã‚  extremely high frequency  Ã‚  Ã‚  Ã‚   30 GHz – 300 GHz  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   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 specifie s a video bandwidth of 5. 0 MHz and an audio carrier at 6 MHz. The DVB-T transmissions 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)  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  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 to 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. Transm ission 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:  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Centre conductor:  Ã‚  Ã‚  Ã‚  Cable diameter:   Ã‚  Ã‚  Ã‚  RG-59  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  20-23 gauge  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  0. 242 inches   Ã‚  Ã‚  Ã‚  RG-6  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  18 gauge  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  0. 265 inches   Ã‚  Ã‚  Ã‚  RG-11  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  14 gauge  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  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 standards. If the mast-mounted amplifier gain exceeds the cable loss then it shouldn’t matte r 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. )  Ã‚  Alternatively, frequency compensated amplifiers will work. 2. 6 Signal Amplifiers There are two types of signal amplifiers: Preamplifiers  Ã‚  (Mast-mounted amplifiers)  Ã‚  Ã¢â‚¬â€œÃ‚  Ã‚  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  Ã‚  Ã¢â‚¬â€œÃ‚  Ã‚  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 overload 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:   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  0. 5 dB  superb (anything better runs into thermal atmospheric noise)   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  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 i ts 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 radians 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 solution The 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 Systems Amplifier 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 input 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 beà ‚  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 Amplifier In 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 than 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 transistor 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 Transistor 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 Cu rrent Gain (hFE). . . . . . . . . . . . . . . . . . . . . . . . . 60 * PNP Early Voltage (VA) . . . . . . . . . . . . . . . . . . . . . . . .20V * Noise Figure (50? ) at 1. 0GHz . . . . . . . . . . . . . . . . . 3. 5dB * Collector to Collector Leakage . . . . . . . . . . . . . . . . . .1pA * Complete Isolation Between Transistors Pin Compatible with Industry Standard 3XXX Series Arrays * Pb-Free Plus Anneal Available (RoHS Compliant) Applications * VHF/UHF Amplifiers * VHF/UHF Mixers * IF Converters * Synchronous Detectors Specifications: * Collector Emitter Voltage V(br)ceo: 8 V * Current Ic Continuous a Max: 11. 3 mA * DC Collector Current: 37 mA * DC Current Gain: 130 * Gain Bandwidth ft Typ: 8 GHz * Module Configuration: Five * Mounting Type: SMD * Number of Pins: 16 * Number of Transistors: 5 * Package / Case: SOIC * Power Dissipation Pd: 150 mW * SVHC: No SVHC (15-Dec-2010) * Supply Voltage Min: 12 V * Transistor Case Style: SOIC * Transistor Polarity: NPN * RoHS: Yes (Datashe et, 2005) Figure 15 HFA3127 transistor array As this project is to design and build a repeater incorporating transmission delay, so any of those or both amplifiers can be used to convert weak high frequency signal to strong signal. 3. 1. 3 Surface mounts technology: Surface mount technology  (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board. SMT components have a flat surface that is soldered to a flat pad on the face of the PCB. Typically, the PCB pad is coated with a paste-like formulation of solder and flux. With careful placement, SMT components on solder paste remain in position until elevated temperatures, usually from an infrared oven, melt the paste and solder the component leads to the PCB pads. Industry-standard pick-and-place equipment can mount SMT components quickly, accurately, and cost-effectively. SMT is a widely used alternative to mounting processes that insert pins or terminals through holes and solder leads into place on the opposite side of the board. 3. 1. 4 Surface Mount Monolithic Amplifier: Figure 16 MAV-11SM amplifier Features: * Wideband, 0. 05 to 1GHz * High output power, up to +17. 5 dBm typ. * Low noise, 3. 6 dB typ. * Aqueous washable * Applications: * UHF – TV * Cellular * Defence communication * UHF/VHF receivers/transmitters (Monolithic Amplifier, 2002) General description: MAV-11SM+ is a wideband amplifier offer a high dynamic range. It has repeatable performance from lot to lot. It is enclosed in a plastic molded package. MAV-11SM+ uses Darlington configuration and is fabricated using silicon technology. Expected MTBF is 500 years at 85 °C case temperature. Functions| Pin number| Description| RF in| 1| RF input pin. This pin requires the use of an external DC blocking capacitor chosen for the frequency of operation. | RF-out and DC-in| 3| RF output and bias pin. DC voltage is present on this pin; therefore a DC blocking capacitor is necessary for proper operation. An RF choke is needed to feed DC bias without loss of RF signal due to the bias connection, as shown in â€Å"Recommended Application Circuit†. | GND| 2,4| Connections to ground. Use via holes as shown in â€Å"Suggested Layout for PCB Design† to reduce ground path inductance for best performance. | (Monolithic Amplifier, 2002) Figure 17 Suggested PCB layout with MAV-11SM 3. 1. 5 Loft box: 8 way home distribution unit * Fully Compatible with the Sky Digital tvLINK System. * Combines Satellite, TV, FM, DAB, CCTV on to one down cable to the living room. * Typically 8dB Gain to each output. * TV, FM Digi Channel, VCR, DAB, CCTV available at each output. * Built in switch mode power supply with LED power on indicator. * The Global LoftBox is an integrated Home Distribution system. Figure 18 Loft box home distributor Normally located in the loft, it combines TV, FM, DAB, CCTV Satellite on to one down cable, feeding to a Global triplexing wall plate or MSWP in the living room. The Loft Box takes a return feed from the living room which would typically be from the UHF2 output from the Sky digibox or from a â€Å"Y† splitter. FM DAB are diplexed onto the return feed then distributed to additional points within the house via Global TV/FM diplex wall plates. Each outlet point is able to receive normal terrestrial TV, FM, DAB, CCTV the selected Satellite channel. The LoftBox fully supports the infrared control signals from the tvLINK remote eye back to the Sky Set-top Box. But for connection problem this could not be used in this project. 3. 1. 6 Maxview signal booster It boosts digital and analogue TV, FM/DAB radio signals in weaker signal areas. This booster was bought for comparing the signal strength with amplifier built in this project. Maxview signal booster is high gain TV signal booster. Key features are; Forward gain typically per outlet: 18dB Switched gain: 6dB Noise figure typically: 4. 5dB Forward frequency coverage: 40-860MHz Reverse frequency coverage: 5-65MHz Figure 19 Maxview signal booster 3. 1. 7 Antenna: Normal TV aerial can be used to receive and transmit signal. For this project Truvision Indoor UHF TV aerial has been selected for receiving and transmitting TV signal. Figure 20 Antenna used for this project The Truvision UHF TV aerial has a striking contemporary free-standing design which simply flips up into position and is ready to use straight out of the box. Easy fingertip adjustment allows horizontal or vertical alignment for optimum signal reception. 4. 0 Design Receiving antenna receives the DVB-T signal and gives it to the repeater. Repeater amplifies the received signal and retransmits the signal through transmission line (coaxial cable). Coaxial cable has been used for incorporating transmission delay to minimize inter symbol interference. Figure 21 Interference between relay signal and main transmitted signal Although this paper talked about strong signal reception by TV antenna but there will be some interference with the transmitted signal from main transmitter. For sjort of time this project could not go through that problem. So this project is now to design the repeater, build the circuit and testing that in laboratory environment and outdoor environment. 4. 1 Circuit design The ISIS schematic drawing software is an extremely versatile application for circuit design. However it naturally takes some time to learn all of its capabilities. For this project HFA3127 transistor array was selected because of its low noise high gain capability. But there was no transistor family named HFA3127 in ISIS software. Then one new transistor family was created to draw the circuit. Figure 22 ISIS schematic of circuit design 4. 2 PCB design Circuit design has been designed in ISIS but PCB layout was not acceptable. It was suggested to design the PCB layout in ARES according to the datasheet. After that, PCB layout was made to ARES. Figure 23 PCB design according to the datasheet in ARES In PCB design there was some contact errors which could not been removed. Whenever it was trying to remove the errors it was saying not connected. As the legs of ICs and other components gap was so small, it was showing that errors. Back side of PCB was grounded plain because this circuit was for RF signal. In PCB design micro strip line has been used for ultra high frequency or very high frequency. Pin no 14 and 15 is connected with RF input socket and pin no 1 and 2 is connected with RF output socket through micro strip. Down side micro strip is for input voltage. Figure 24 3D view for PCB 5. 0 Implementation Required components: * PCB board * Resistors * Capacitors * Amplifier * Two antennas * TV card * Transmission line (Coaxial cable) * SMA connectors 5. 1 Implementation with HFA3127 As it was the circuit of surface mount components, it was really difficult to solder by hand. Components were 0603 package so it was very small. Even it is mentioned earlier in ISIS there was no package for HFA3127 so it had to make one package for this device. The dimensions of ICs legs were wrong so the IC was not fitted with PCB board. One side of ICs legs were fitted and other side’s legs were connected with small wire. Figure 25 Circuit with HFA3127 amplifier 5. 2 Implementation with MAV-11SM amplifier This amplifier has been designed with MAV-11SM amplifier. This picture shows two amplifiers have been used for this circuit but actually two amplifier circuit has been joined together to get more gain. This is also surface mount circuit board. This amplifier’s gain is 10dB each. Figure 26 MAV-11SM amplifier circuit board As this paper was expecting an amplifier with more than 30dB reverse gain so HFA3127 has been also connected with these two. 6. 0 Test result 6. 1 Laboratory test result Amplifier circuit with HFA3127: Figure 27 HFA3127 gain with soldering error Figure 28 HFA3127 amplifier gain Amplifier circuit with MAV-11SM: Figure 29 One MAV-11SM amplifier gain Figure 30 Two MAV-11SM amplifier circuits give more gain Figure 31 Three amplifiers together was the maximum gain 6. 2 Field test result Figure 32 Low quality picture with normal antenna Figure 33 Picture with repeater connected antenna Figure 34 Rebroadcasting connection 7. 0 Result Discussion Laboratory test: Results with transistor array: Figure-27 shows the return loss is -6. 2573 dB at input power -20dB in the place of 15-20 dB. From this result it was understood that something problem with soldering. After examining the circuit soldering, it was found that at pin 4 the voltage is 0V instead of 0. 7-0. 8V. Then it was soldered again and checked it. This time it was 0. 8V but still it was not ok. After that from supervisor suggestion, transistor was changed to amplify the signal. This time the gain was high 25 dB but it was rolling over. Figure-28 shows initial gain was 25 dB but it was rolling over. The average gain was nearly 10 dB. According to data sheet this gain should be 15-20 dB. Probably if the soldering would very good, it would be possible to get good result with this amplifier. Even if it is possible to use all five transistors at a time then it is very possible to get 120 dB gains which are really incredible. Results with MAV-11SM amplifier: Figure-29 shows MAV-11SM amplifier circuit was working expectedly. With one amplifier its gain should be around 10 dB. It was showing 8. 94 dB. Figure-30 shows when two MAV-11SMs was connected together the gain was increased to 15. 93dB at -20 dBm power. Now it was connected three amplifiers together and the gain was burst! Figure-31 shows the gain was 31. 276 dB for which the project was waiting. Field Test Now time to outdoor test, for outdoor test a TV card/TV, three antennas, and coaxial cable were needed with repeater. First, TV card was installed in the computer and connected with antenna without amplifier. After scanning the channel, only 6 free channels were found and most of their picture qualities were very low (figure-32). After that the repeater was connected with antennas and directly connected with TV card. Now it got 67 free channels from scanning and the picture quality was very high (figure-33). When voltage was keeping 0V from power supply connected with repeater, the picture was becoming worse and when voltage was going to be high the picture quality was going to high. Now the final stage of testing, because until now it can be said that repeater is working perfect. But the purpose the repeater has been built is to rebroadcast the signal. For rebroadcasting the signal input side of the repeater was connected with one receiver antenna and output side was connected with transmitter antenna with long transmission line (figure-34) which would incorporate delay to minimize inter symbol interference. But it was connected for 24 hours and TV was on with normal antenna but no improvement was made by rebroadcasting issue. End of this experiment it was found that probably the transmit power was too low to retransmit the signal because power supply was 5V 1A input or the antenna could not transmit the signal around the room or antenna transmitted too low signal that the signal was not good enough to capture good quality video. Two possible reasons for failure: * Too low power for retransmit * Transmit antenna Time was a big factor for test. According to Gantt chart, only 20 days have been used for testing because of all other assignment. This delay was coming from previous task as well. Design and implementation took a long time. When testing has been started, then there was not extra time to resolve any problem identified. 8. 0 Conclusion The aim of this project was to design a digital repeater incorporating transmission delay (coaxial cable) to minimize inter symbol interference. The project main part was to design an amplifier circuit, build the circuit and test the circuit. If everything goes right then it can be tested by rebroadcasting DVB-T signal checked in TV. Though this project has not reached its final target, still this project is a complete concept of amplify signal theory. At the very beginning this project was expecting to design a digital repeater which will minimize inter symbol interference incorporating transmission delay. At first, HFA transistor array has been selected for designing amplifier where the circuit was built by surface mount components. For soldering problem the gain was -5dB. After that only one transistor has been used from five transistors of HFA3127 by supervisor’s suggestion to get good performance. Though initially that design gave 25 dB gains but it was rolling over. Still average gain of HFA3127 was 10 dB. As for high frequency amplifying and transmission needs a very high gain amplifier (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 repeater 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 Cited Antenna 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 Interferance (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| 525. 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| How to cite Design a Repeater for Digital Rf Signal, Essay examples

Why does group polarisation occur Essay Example

Why does group polarisation occur Essay Group polarisation refers to the tendency for groups to make more extreme decisions or judgements after discussion when compared to the initial views of group members. This phenomenon has interested psychologists since 1961, when Stoner discovered the risky shift, and is central to understanding social influence in groups; therefore the major theories of social influence have been invoked to explain it, so far with little conclusive success. This essay will cover the origins of group polarisation and examples of it in everyday life, and will then proceed to discuss a number of theories proposed to explain it. It will then be attempted to ascertain which of these best explains group polarisation and why. Until the 1960s it was generally accepted that a groups attitudes were the mean or average of its comprising individuals attitudes. In 1961 Stoner asked some business students to make judgements on a choice dilemma questionnaire, this was done individually and then in groups. Group decisions were found to be, on average, more risky than average pre-discussion, individual decisions. This was known as the shift to risk, and was quickly replicated by Wallach et al. (1962). Wallach et al. evised twelve hypothetical choice dilemmas, and asked participants to rate the lowest level of risk that they found acceptable for somebody to take a risky course of action. They found that 92% of group decisions were riskier than the average individual decision; and importantly, that it resulted in permanent cognitive change, with 39% taking riskier actions after the group decisions (Wallach and Kogan, 1965). Early explanations for this shift were based around the idea that groups have a diffusion of responsibility; with no-one individually held responsible, they can afford to take risks. We will write a custom essay sample on Why does group polarisation occur specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Why does group polarisation occur specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Why does group polarisation occur specifically for you FOR ONLY $16.38 $13.9/page Hire Writer However, the shift to risk was soon found to be a shift to extremity, with several experiments finding that groups are not always risky. Stoner (1968) found reliable shifts to caution on issues of well being and safety; e. g. prisoner to attempt escape, if the prisoner escapes he lives, but if not he will die. It was concluded that groups polarise, they shift to extremities, the more extreme a group is to begin with, the more extreme it seems to become (Brown, 2000, p. 199). This was a very important discovery which challenged the classic conformity theory experiments which typically showed convergence on the group norms. Sherifs 1935 auto kinetic experiment showed groups converging on a range of judgements close to the mean or median of preliminary individual judgements. Aschs line experiments produced similar results (1952, 1955 1956). The risky shift experiments show simultaneous convergence and shift to a more extreme group norm be it negative or positive. Polarisation doesnt just occur in theoretical choice dilemmas, it is a general phenomenon that may be observed in everyday life. Kalven and Ziesel (1966) studied jury decisions in America and found that the initial majority were predictive of 90% of decisions. Blacovich et al. (1975) found that groups bet more than individuals in Blackjack; while McCauley et al. found groups to be more cautious than individuals when betting on horses. Moscovici and Zavalloni (1969) asked French students their attitudes towards President de Gaulle and the USA, the students then formed groups and gave group attitude responses. These group responses were more extreme than their individual responses with de Gaulle being seen more positively and the USA more negatively than previously. However, almost all the studies conducted into group polarisation have been within laboratories using ad-hoc groups and with no realistic outcome for the participants. Therefore it could be argued that these results cannot be generalised Of the experiments that have been conducted with real-experiment groups, the results have been less reliable (e. g. Semin and Glendon, 1973) though it is a phenomenon that is occurring regularly. The first theory that tried to account for group polarisation was by Wallach and Kogan (1965); based on diffusion of responsibility, they held that discussion reduced any anxiety felt about the negative consequences of making a choice, because the responsibility is shared. This didnt explain why shifts to caution or shifts on decisions which resulted in no consequences occurred. The group decision schemes theory (Davis, 1979), was one of the first influential theories in the field; Davis held that groups have implicit rules for combining individual positions on decisions; the most common rule being majority rule. This means the group decision will be more extreme or skewed whenever the majority is biased towards a particular extreme. There were many criticisms levelled at the theory which didnt adequately resolve why polarisation actually occurred. It was rejected, as skewness does not account for shifts in dyads where no majority can exist; it doesnt explain why there are shifts in the group median as well as the mean and the shift may also runs counter to the initial majority. Also it didnt justify why the group shift was internalised and even affected non-participating observers (Lamm, 1967). Lastly, as Graesser (1975) points out, the theory is not falsifiable because group decision schemes theory is based upon infinite maths calculations and therefore it is always possible to claim that the correct scheme has yet to be discovered. A number of other theories were proposed, including familiarisation theory (Bateson, 1965) and various leadership theories, none proved to be watertight and were dismissed. Only two theories have survived and both have tended to rework one of the two dual processes recognised by the social dependency paradigm: normative and informational influence. First we shall consider normative influence and social comparison theory; an extension of Festingers (1954) social comparison theory, Sanders and Baron (1977) have modified it to explain polarisation. Normative influence is being liked; fulfilling and conforming to the groups expectations so as to boost positive feeling about oneself. Sanders and Baron tried to prove that people often value more extreme values than they actually hold; however they are generally scared of being too extremist. However when in a group it is actually found that they hold only moderate views, and so shift them further in the group direction to be seen more positively. The key factor in this social comparison explanation is peoples knowledge of other group members positions relative to the dominant social values in question (Brown, 2000, p. 202). Therefore, as Teger and Pruitt (1967) found, there is no need for any discussion, as long as group members positions can be inferred, their will be no need for a verbal exchanging of views. As the values become more explicit so people polarise more extremely; Baron and Roper (1976) adapted Sherifs (1936) auto kinetic effect paradigm by effectively informing participants that light distance was correlated with high intelligence. This inevitably led to participants estimating higher distances depending upon the claim made by the participant beforehand. However Burnstein and Vinokur (1977) claim that by associating light movement with intelligence, they have provided the participants with a persuasive argument to estimate larger distances (Burnstein and Vinokur, 1977, p. 27). Burnstein and Vinokur have taken a totally opposing stance towards solving the polarisation phenomenon. They hold that it is a result of informational influence, of persuasive arguments which cause people to accept information as the truth. Vinokur and Burnsteins persuasive arguments theory (1974) holds that a culturally given pool of arguments exist for and against the decision in question, which participants can delve into and exchange during discussion. For a shift to occur it depends upon the persuasiveness of the new arguments generated in discussions. However, availability, direction and persuasiveness of these arguments vary, which may allow for experiments whereabouts the arguments do not result in group polarisation. A persuasive argument is defined as a statement judged to have a certain cogency (Burnstein and Vinokur, 1977, p. 326), but the arguments impact can only be effective within certain social contexts; for otherwise it wouldnt be possible to determine its impact. Sanders and Baron have conceded that a persuasive argument also has an effect on group polarisation, and that the two theories work in conjunction with one another. This was rejected on the grounds that it was too complicated and that persuasive arguments can explain polarisation and convergence. There is a huge wealth of evidence lending credence to the persuasive arguments theory; including polarisation when exposed to arguments without exposure to others positions and polarisation when just thinking about an issue. Burnstein and Vinokur found that (i) if an individual could argue but not compare, then polarisation occurred (1973), (ii) if he could compare but not argue, polarisation vanishes or is greatly reduced (1973, 1975). Burnstein et al. conceded that social comparison may play an indirect role in influencing polarisation as information about others may guide the person in generating arguments (Burnstein and Vinokur, 1977, p. 318). Myers and Lamm also disagree with the persuasive arguments theory, they concluded that (although) the evidence for (informational theories such as persuasive arguments) is compelling it also appears that group polarisation is not fully explained by a passive process of cognitive learning. More dynamic processes of cognitive rehearsal and verbal commitment are also likely contributors (Myers and Lamm, 1976 cited in Burnstein and Vinokur, 1977, p. 316). Burnstein and Vinokur argue that this is invalid because persuasive arguments involves a dynamic process whereabouts the persons brain acts like a central processing unit. Another criticism of the persuasive arguments theory is that their research generally involves the use of choice dilemma questionnaires introduced by Kogan and Wallach (1964); as these only measure shifts involving a risk-caution dimension they cant really be used to generalise to choice shifts in general. Many debates have taken place between exponents of the social comparison theory and the persuasive arguments theory ultimately leading to an inconclusive end. An alternative to Turners (1987) self categorisation theory, formulated by Wetherell (1987), proposes that for convergence to lead to polarization rather than just conformity; arguments have to be persuasive and extreme positions desirable only to the degree that they represent the norms of a group with which the person is psychologically identified. What group members converge upon is not the ingroup average, but the ingroup norm. This idea was tested on students by Mackie and Cooper (1984) who confirmed that participants attitudes were significantly more affected when they knew the arguments were coming from an ingroup rather than an outgroup. Sanders and Baron admit that there are probably several processes responsible for group induced choice shifts (Sanders Baron, 1977, p. 303). Burnstein and Vinokur still remain convinced that persuasive arguments can adequately explain group polarisation; but in conclusion (and as Lamm and Myers (1978) deduce) in a naturalistic setting there is no neat dichotomy. There is no clear cut separation between the two main theories, they operate unconsciously within each other and therefore both are necessary in daily life, probably along with several other factors, in order to produce the phenomenon known as group polarisation.