DOCSLIB.ORG

A Double-Edged Sword Be Smart When You Design a Climate Room

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Double-Edged Sword Be Smart When You Design a Climate Room BY THEO TEKSTRA, MARKETING MANAGER GAVITA HOLLAND EMI CAN DISRUPT OR DEGRADE THE FUNCTIONING OF OTHER ELECTRONIC DEVICES E.M.I. A DOUBLE-EDGED SWORD BE SMART WHEN YOU DESIGN A CLIMATE ROOM The introduction of high frequency electronic remote ballasts into the market has created a new problem: electromagnetic interference (EMI). EMI consists of high frequency signals which are either conducted (through for example your power cord back to the grid), or emitted in the form of radio waves (for example by your lamp cord connecting a high frequency remote ballast to the lamp). EMI can disrupt or degrade the functioning of other electronic devices. In some cases, this may even lead to life threatening situations, for example, if medical systems or emergency communication systems are influenced. So what is that EMI, and what can we do to avoid it? What are the rules and regulations? 74 E.M.I. I GARDEN CULTURE Standards Let’s get the dull stuff out of the way first: there are two classes which define how much EMI a device may emit: a) Class A for industrial use - Conducted EMI travels through the power cord of the b) Class B for residential or medical use device back to the grid, and is distributed over your mains ca- In industrial environments the EMI levels are allowed to be bles. All devices that are plugged into the same mains supply a bit higher. Class B, for residential use, is more strict than will receive this automatically. The interference does not stop the industrial standard. In Europe, as well as North America, at your house though: a complete block of houses or more, class A and B are used, and are connected to the same supply, can very similar. Manufacturers of THE INTERFERENCE be influenced. The frequencies are I. electrical devices need to make approximately 9 kHz to 30 MHz. sure they do not emit more than DOES NOT STOP AT Radiated EMI can, for example, the applicable standard. YOUR HOUSE hinder cell phone reception, wire- less devices such as intercom sys- EMI, however, is a double-edged sword: manufacturers of tems, monitoring systems and radio amateurs, but it can also electronic devices should also make sure that their electri- induce bad readings of sensitive instruments such as pH and cal devices are protected against the influence of EMI from ec meters. A DOUBLE-EDGED SWORD other apparatus to a certain degree. This, of course, makes Conducted EMI can influence anything that is connected to things a bit more complicated. Interference you experience the same mains supply, and can cause routers to disconnect, is not necessarily from a device emitting too much, it could computers to fail, loss in data, interference on audio and ca- BE SMART WHEN YOU DESIGN A CLIMATE ROOM well be that the receiving device is not sufficiently protected ble TV systems, etc. against EMI. Of the two, the conducted EMI may well be a worse problem than the emitted EMI. There are many devices that emit EMI, because they emit radio frequent radiation, for example, cell phones and radio transmitters. In certain environments it is therefore not al- Electronic ballasts and EMI lowed to use these, because they would possibly interfere Electronic ballasts have become popular because they are with sensitive systems. Examples are radio studios and the- efficient, lightweight, run relatively cool, provide a stable aters (interference with audio systems and wireless micro- output regardless of mains voltage fluctuations, and can be phones), hospitals and airplanes (possible interference with controlled. Traditional (low frequency) core-coil ballasts are critical electronic systems). Still, these devices all comply to quite heavy and become very warm. They can be noisy, as regulations. in humming, and some components degrade over time. But they are cheap, reliable, and cause no interference whatso- ever, because they work on the mains frequency: 50/60 Hz! Radiated and conducted EMI So why don’t manufacturers make a low frequency electronic There are two different types of EMI: ballast? They do. - Radiated EMI works like radio waves, and is emitted by There are low frequency electronic ballasts as well. Because the equipment like a radio transmitter. Radio waves are very of the electronic nature of the ballast they can still cause EMI high frequency: frequencies from 30 kHz and up (long wave) though, and because of the low frequency they are often big can cause radiated interference. Medium wave, for example, and more expensive. Especially square wave low frequency ranges from approximately 500 kHz to 1.7 MHz. This emis- ballasts can be noisy on lamps, resulting in (literally!) vibrating sion can be picked up by devices that are sensitive to these arc tubes. They are also less efficient than high frequency bal- frequencies, without any electrical connection to the device lasts, and more expensive to produce. generating the EMI. gardenculturemagazine.com 75 Then there is a huge variety in operating frequency: traditional high frequency ballasts work around 35 kHz, but modern hor- Low versus high frequency ticultural double ended systems, for example, work at 120 kHz! It’s not only this base frequency that causes the problems. High Magnetic ballasts output the same frequency as the re- frequency equipment generates what we call harmonics, much ceive from mains, so 50 Hz in Europe, 60 Hz in the USA. higher frequencies than the base frequency. They easily reach This causes a “flicker” in the light, which actually switches the radio frequent spectrum your other devices are sensitive to. on and off 100/120 times per second. On digital photo- Harmonics are mostly responsible for emitted EMI problems. graphs you see this as light and dark banding. High fre- Sine wave and square wave both have higher harmonic frequen- quency electronic ballasts switch so fast that the arc in the cies. High frequency square wave ballasts in particular generate arc tube does not extinguish any more, leading to a higher lots of harmonics and EMI. output, and better efficiency. How to avoid EMI It is almost impossible to avoid EMI with a high frequency re- higher frequency, possibly even destroying the ballast. This is mote ballast. The lamp cord connecting the (metal shielded) why in horticulture only complete fixtures are used, with ballast ballast to the reflector is the biggest problem for radiated EMI: and reflector integrated. The lamp cables are integrated in the it works like an antenna. The longer the cord the bigger the an- metal design, reducing the interference to a minimum. tenna. Shielding the lamp cord is not a solution in many cases, as Conducted EMI is caused by insufficient filtering inside the bal- it dampens the ignition pulse and can lead to lamps not starting last, or just plain bad design, causing high frequency signals to be any more, causes losses in output signal, and in some cases, it delivered back to the grid. This can happen in remote ballasts, actually causes the frequency of the ballast to go up to a much as well as complete fixtures. Down to Earth Tel: +44 (0) 1223 610021 Email: [email protected] D E Kent Ltd Tel: +44 (0) 1223 500633 Website: www.downtoearthkent.co.uk E.M.I. I GARDEN CULTURE There are several ways to keep your EMI to a minimum: HARMONICS ARE MOSTLY RESPONSIBLE FOR EMITTED 1. Best option: use complete fixtures! Ballast and reflector are integrated, so there is no loose lamp cord to emit lots of EMI. EMI PROBLEMS Also they are much easier to wire than remote systems. You just need to bring power to your climate room. 2. Make sure you have a good earth connection. The use of a protective earth connection is crucial to avoid EMI in shielded systems. Always use protective earth for safety, but specifically for high frequency devices to provide good shielding. 3. Keep lamp cords as short as possible, so keep the ballasts as close to the reflector as possible. And here I am talking about just 15 cm of cable instead of 5 meters or more! 4. Keep lamp cords apart from mains cords. If you they cross or run parallel you can get induction of the high frequency out- put on your mains supply, causing conducted EMI. This feedback signal can even destroy your ballast. 5. Never coil your lamp cords, make them too short! A coil EMI measuring rooms ideally do not contain metal objects close to the sources, de tables on which the objects are placed are made of wood. can influence the frequency of your ballast, and can amplify radi- ated EMI. Keep your family and So, what should I buy? neighbors happy and safe If a device carries an FCC or CE sign it should be compliant EMI can cause all kinds of mayhem in a domestic environment: to the EMI regulations. I say should be, as in reality there are Internet routers that lose connection, Wi-Fi access points that a lot of things wrong with the testing of electronic equipment. decrease in performance or lose connection, TV’s and satellite For CE, for example, the manufacturer may choose to test receivers that show interference, remote controls (for example, the equipment himself, and declare that it is compliant to CE. to open your garage door or arm your alarm system) that do If it turns out that it isn’t compliant he will probably get a slap not work anymore, intercom systems that become unusable be- on the wrist, which in many cases is cheaper than being really cause of a loud hum, false alarms in wireless systems, amateur compliant.
Load more

Recommended publications
  • Kindergarten High Frequency Word List
    Kindergarten High Frequency Word List The following 40 words are the high frequency Kindergarten words. They are divided according to their probability of occurring in the corresponding DRA text levels. However, many of these words can occur throughout all levels. The goal is for all students to read, write, and use these words correctly by the end of Kindergarten. Level 1 Level 2 Level 3 Level 4 Level 5 a me to yes big I go in cat for is at on dog he the you like up she mom we my with this dad it by said look can no love play went see am do was and C:\Users\metcalfr\Downloads\K_5_High_Frequency_Word_Lists (2).docx October 2014 First Grade High Frequency Word list The goal is for all students to read, write, and use these words (and words from the kindergarten word list) correctly by the end of first grade. after have please all her saw an here should are him so as his some be I’m thank because if that but into them came just then come know they could little there day make us did many very end new want from not were get of what goes one when going or where good our who had out will has over would your C:\Users\metcalfr\Downloads\K_5_High_Frequency_Word_Lists (2).docx October 2014 Second Grade High Frequency Word List The goal is for all students to read, write, and use these words (and the words from preceding grade level word lists) correctly by the end of second grade.
    [Show full text]
  • High Frequency Communications – an Introductory Overview
    High Frequency Communications – An Introductory Overview - Who, What, and Why? 13 August, 2012 Abstract: Over the past 60+ years the use and interest in the High Frequency (HF -> covers 1.8 – 30 MHz) band as a means to provide reliable global communications has come and gone based on the wide availability of the Internet, SATCOM communications, as well as various physical factors that impact HF propagation. As such, many people have forgotten that the HF band can be used to support point to point or even networked connectivity over 10’s to 1000’s of miles using a minimal set of infrastructure. This presentation provides a brief overview of HF, HF Communications, introduces its primary capabilities and potential applications, discusses tools which can be used to predict HF system performance, discusses key challenges when implementing HF systems, introduces Automatic Link Establishment (ALE) as a means of automating many HF systems, and lastly, where HF standards and capabilities are headed. Course Level: Entry Level with some medium complexity topics Agenda • HF Communications – Quick Summary • How does HF Propagation work? • HF - Who uses it? • HF Comms Standards – ALE and Others • HF Equipment - Who Makes it? • HF Comms System Design Considerations – General HF Radio System Block Diagram – HF Noise and Link Budgets – HF Propagation Prediction Tools – HF Antennas • Communications and Other Problems with HF Solutions • Summary and Conclusion • I‟d like to learn more = “Critical Point” 15-Aug-12 I Love HF, just about On the other hand… anybody can operate it! ? ? ? ? 15-Aug-12 HF Communications – Quick pretest • How does HF Communications work? a.
    [Show full text]
  • High-Frequency Radiowa Ve Probing of the High-Latitude Ionosphere
    RAYMOND A. GREENWALD HIGH-FREQUENCY RADIOWAVE PROBING OF THE HIGH-LATITUDE IONOSPHERE During the past several years, a program of high-frequency radiowave studies of the high-latitude ionosphere has been developed in the APL Space Department. Studies are now being conducted on the formation and motion of high-latitude ionospheric electron density irregularities, using a sophisti­ cated high-frequency radar system installed at Goose Bay, .Labrador. The radar antenna is also being used to receive signals from a beacon transmitter located at Thule, Greenland. This information is providing a better understanding of the spatial and temporal variability of high-latitude propagation channels and their relationship to disturbances in the magnetosphere-ionosphere system . INTRODUCTION turbances prior to their impingement on the magneto­ At altitudes above 100 kilometers, the atmosphere sphere is quite limited. Therefore, we still have only of the earth gradually changes from a predominantly limited success in forecasting sudden changes in the neutral medium to an increasingly ionized gas or plas­ high-latitude ionosphere and consequently in high­ ma. The ionization is caused chiefly by a combination latitude radiowave propagation. of solar extreme ultraviolet radiation and, at high lati­ In order for space scientists to obtain a better un­ tudes, particle precipitation from the earth's magne­ derstanding of the various interactions occurring tosphere. Because of its ionized nature between 100 among the solar wind, the magnetosphere, and the ion­ and 1000 kilometers, this part of the atmosphere is osphere, active measurement programs are conduct­ commonly referred to as the ionosphere. In this re­ ed in all three regions.
    [Show full text]
  • UNIT -1 Microwave Spectrum and Bands-Characteristics Of
    UNIT -1 Microwave spectrum and bands-characteristics of microwaves-a typical microwave system. Traditional, industrial and biomedical applications of microwaves. Microwave hazards.S-matrix – significance, formulation and properties.S-matrix representation of a multi port network, S-matrix of a two port network with mismatched load. 1.1 INTRODUCTION Microwaves are electromagnetic waves (EM) with wavelengths ranging from 10cm to 1mm. The corresponding frequency range is 30Ghz (=109 Hz) to 300Ghz (=1011 Hz) . This means microwave frequencies are upto infrared and visible-light regions. The microwaves frequencies span the following three major bands at the highest end of RF spectrum. i) Ultra high frequency (UHF) 0.3 to 3 Ghz ii) Super high frequency (SHF) 3 to 30 Ghz iii) Extra high frequency (EHF) 30 to 300 Ghz Most application of microwave technology make use of frequencies in the 1 to 40 Ghz range. During world war II , microwave engineering became a very essential consideration for the development of high resolution radars capable of detecting and locating enemy planes and ships through a Narrow beam of EM energy. The common characteristics of microwave device are the negative resistance that can be used for microwave oscillation and amplification. Fig 1.1 Electromagnetic spectrum 1.2 MICROWAVE SYSTEM A microwave system normally consists of a transmitter subsystems, including a microwave oscillator, wave guides and a transmitting antenna, and a receiver subsystem that includes a receiving antenna, transmission line or wave guide, a microwave amplifier, and a receiver. Reflex Klystron, gunn diode, Traveling wave tube, and magnetron are used as a microwave sources.
    [Show full text]
  • HF Radio Propagation
    Introduction to HF Radio Propagation 1. The Ionosphere 1.1 The Regions of the Ionosphere In a region extending from a height of about 50 km to over 500 km, most of the molecules of the atmosphere are ionised by radiation from the Sun. This region is called the ionosphere (see Figure 1.1). Ionisation is the process in which electrons, which are negatively charged, are removed from neutral atoms or molecules to leave positively charged ions and free electrons. It is the ions that give their name to the ionosphere, but it is the much lighter and more freely moving electrons which are important in terms of HF (high frequency) radio propagation. The free electrons in the ionosphere cause HF radio waves to be refracted (bent) and eventually reflected back to earth. The greater the density of electrons, the higher the frequencies that can be reflected. During the day there may be four regions present called the D, E, F1 and F2 regions. Their approximate height ranges are: • D region 50 to 90 km; • E region 90 to 140 km; • F1 region 140 to 210 km; • F2 region over 210 km. At certain times during the solar cycle the F1 region may not be distinct from the F2 region with the two merging to form an F region. At night the D, E and F1 regions become very much depleted of free electrons, leaving only the F2 region available for communications. Only the E, F1 and F2 regions refract HF waves. The D region is very important though, because while it does not refract HF radio waves, it does absorb or attenuate them (see Section 1.5).
    [Show full text]
  • International High Frequency Broadcasting Agreement (Mexico
    This electronic version (PDF) was scanned by the International Telecommunication Union (ITU) Library & Archives Service from an original paper document in the ITU Library & Archives collections. La présente version électronique (PDF) a été numérisée par le Service de la bibliothèque et des archives de l'Union internationale des télécommunications (UIT) à partir d'un document papier original des collections de ce service. Esta versión electrónica (PDF) ha sido escaneada por el Servicio de Biblioteca y Archivos de la Unión Internacional de Telecomunicaciones (UIT) a partir de un documento impreso original de las colecciones del Servicio de Biblioteca y Archivos de la UIT. (ITU) ﻟﻼﺗﺼﺎﻻﺕ ﺍﻟﺪﻭﻟﻲ ﺍﻻﺗﺤﺎﺩ ﻓﻲ ﻭﺍﻟﻤﺤﻔﻮﻇﺎﺕ ﺍﻟﻤﻜﺘﺒﺔ ﻗﺴﻢ ﺃﺟﺮﺍﻩ ﺍﻟﻀﻮﺋﻲ ﺑﺎﻟﻤﺴﺢ ﺗﺼﻮﻳﺮ ﻧﺘﺎﺝ (PDF) ﺍﻹﻟﻜﺘﺮﻭﻧﻴﺔ ﺍﻟﻨﺴﺨﺔ ﻫﺬﻩ .ﻭﺍﻟﻤﺤﻔﻮﻇﺎﺕ ﺍﻟﻤﻜﺘﺒﺔ ﻗﺴﻢ ﻓﻲ ﺍﻟﻤﺘﻮﻓﺮﺓ ﺍﻟﻮﺛﺎﺋﻖ ﺿﻤﻦ ﺃﺻﻠﻴﺔ ﻭﺭﻗﻴﺔ ﻭﺛﻴﻘﺔ ﻣﻦ ﻧ ﻘ ﻼً 此电子版（PDF版本）由国际电信联盟（ITU）图书馆和档案室利用存于该处的纸质文件扫描提供。 Настоящий электронный вариант (PDF) был подготовлен в библиотечно-архивной службе Международного союза электросвязи путем сканирования исходного документа в бумажной форме из библиотечно-архивной службы МСЭ. INTERNATIONAL HIGH FREQUENCY BROADCASTING AGREEMENT Mexico City, 1949 FINAL PROTOCOL ANNEXED TO THE INTERNATIONAL HIGH FREQUENCY BROADCASTING AGREEMENT MEXICO CITY PLAN OF THE DISTRIBUTION OF CHANNEL HOURS FOR HIGH FREQUENCY BROADCASTING ANNEXED TO THE INTERNATIONAL HIGH FREQUENCY BROADCASTING AGREEMENT BASi.C_.PL A N INTERNATIONAL TELECOMMUNICATION UNION, G April 1949 Note of the General Secretariat of the I#T,U# The following divergencies were found between the English text of the Mexico City Agreement and the French text which is authoritative: Page 2A. § 5, 3rd line, read: • #••# and, in the Interest of these administrations, ask all administrations ••##.• III# Terms of reference, a), 5th-6th lines, read: This index shall be determined by the T#P#C# Page 31.
    [Show full text]
  • Satellite Communications in the New Space
    IEEE COMMUNICATIONS SURVEYS & TUTORIALS (DRAFT) 1 Satellite Communications in the New Space Era: A Survey and Future Challenges Oltjon Kodheli, Eva Lagunas, Nicola Maturo, Shree Krishna Sharma, Bhavani Shankar, Jesus Fabian Mendoza Montoya, Juan Carlos Merlano Duncan, Danilo Spano, Symeon Chatzinotas, Steven Kisseleff, Jorge Querol, Lei Lei, Thang X. Vu, George Goussetis Abstract—Satellite communications (SatComs) have recently This initiative named New Space has spawned a large number entered a period of renewed interest motivated by technological of innovative broadband and earth observation missions all of advances and nurtured through private investment and ventures. which require advances in SatCom systems. The present survey aims at capturing the state of the art in SatComs, while highlighting the most promising open research The purpose of this survey is to describe in a structured topics. Firstly, the main innovation drivers are motivated, such way these technological advances and to highlight the main as new constellation types, on-board processing capabilities, non- research challenges and open issues. In this direction, Section terrestrial networks and space-based data collection/processing. II provides details on the aforementioned developments and Secondly, the most promising applications are described i.e. 5G associated requirements that have spurred SatCom innovation. integration, space communications, Earth observation, aeronauti- cal and maritime tracking and communication. Subsequently, an Subsequently, Section III presents the main applications and in-depth literature review is provided across five axes: i) system use cases which are currently the focus of SatCom research. aspects, ii) air interface, iii) medium access, iv) networking, v) The next four sections describe and classify the latest SatCom testbeds & prototyping.
    [Show full text]
  • Historical Survey of Fading at Medium and High Radio Frequencies
    PB161634 *#©. 133 jjoulder laboratories HISTORICAL SURVEY OF FADING AT MEDIUM AND HIGH RADIO FREQUENCIES BY *- ROGER &. SALAIS4AN U. S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS THE NATIONAL BUREAU OF STANDARDS Functions and Activities The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the na- tional standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agen- cies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic and applied research, development, engineering, instrumentation, testing, evaluation, calibration services, and various consultation and information services. Research projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover. Publications The results of the Bureau's research are published either in the Bureau's own series of publications or in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections, presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining the best frequencies to use for radio communications throughout the world.
    [Show full text]
  • High Frequency Words
    High Frequency Words High-frequency words are the words that appear most often in printed materials. Students are encouraged to recognize these words by sight, without having to “sound them out.” Learning to recognize high-frequency words by sight is critical to developing fluency in reading. Students should be able to read these words individually and in sentences and stories. Automatic recognition of high frequency words provides an essential starting point for your child becoming a confident reader. It is important to note that 12 high frequency words make up 25% of words we read and write. 100 high frequency words make up 50% of words we read and write. about 300 high frequency words account for 75% of words we read and write. Seven Simple Tips to Help Your Child Learn High-Frequency Words 1. Write high-frequency words on index cards. Click on the grade levels below for printable word cards. a. PreK word cards b. Kindergarten cards c. First Grade cards d. Second Grade cards e. Third Grade cards 2. Help your child create sentences with the index cards. (ex. Look at me. I like red.) 3. Have your child say or write sentences using each word. 4. Have your child write the words in shaving cream, play dough, sand, or sugar. 5. Add movement when reading or spelling the words. For example, if the word is look, your child says look three times while jumping, clapping, stomping, or snapping fingers. 6. Read a story to your child. After reading, have him/her find the high frequency words on each page.
    [Show full text]
  • Fading Correlation Bandwidth and Short-Term Frequency Stability Measurements on a High-Frequency Transauroral Path
    *>Uo„al Bureau of standard library, ». w . Bldg FEB 4 1963 ^ecknical v2©te 165 FADING CORRELATION BANDWIDTH AND SHORT-TERM FREQUENCY STABILITY MEASUREMENTS ON A HIGH-FREQUENCY TRANSAURORAL PATH J. L. AUTERMAN U. S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS THE NATIONAL BUREAU OF STANDARDS Functions and Activities The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the na- tional standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,- devices, and structures; advisory services to government agen- cies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic and applied research, development, engineering, instrumentation, testing, evaluation, calibration services, and various consultation and information services. Research projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover. Publications The results
    [Show full text]
  • Introduction to Wireless Electromagnetic Channels & Large
    EE-546 Wireless Communication Technologies Spring 2005 Introduction to Wireless Electromagnetic Channels & Large Scale Fading* Rahul N. Pupala [email protected] Department of Electrical Engineering – Rutgers University, Piscataway, NJ 08854 Abstract- This article provides a brief introduction to atmosphere reflects, absorbs or scatters radio waves. wireless channels – frequency range classification of the The layers most relevant to terrestrial radio propagation electromagnetic spectra and large-scale propagation in are shown in fig 1 below. such channels. I. INTRODUCTION/MOTIVATION The term wireless communication refers to the transfer of information using electromagnetic (EM) or acoustic waves over the atmosphere rather than using any propagation medium that employs wires. Not requiring an explicit network of wires and permitting communication while on the move were the main factors which motivated the study of wireless th communication in the early 20 century. Wireless communication evolved remarkably since Fig 1: Atmospheric Layers relevant to terrestrial radio Marconi first demonstrated radio’s ability to provide propagation. continuous contact with ships sailing the English Channel in 1897. Since then, particularly during the last The troposphere is the first layer above the surface decade, the mobile radio communications industry has of the earth, and contains approximately half of the grown by orders of magnitude fueled by digital and RF earth’s atmosphere. This is the layer at which weather circuit fabrication and miniaturization techniques that takes place. The ionosphere is where ions and electrons make portable radio equipment smaller, cheaper and exist in sufficient quantities to reflect and/or refract the more reliable. Digital switching techniques have radio waves.
    [Show full text]
  • High Frequency Words
    High and Medium Frequency Words This resource is designed to support the teaching and marking application of AO6. These lists can be amended by deleting or adding words to make them relevant for your students. The lists can be used diagnostically to test a student's ability to recognise and spell each word. Equally, they can be used as a reference guide when marking the writing tasks of each NEA. High frequency words I up look we like and on at for he is said go you are this going they away play a am to come day the big my mum no dad all get in went was of me she see it(s) yes can about after again an another as back ball be because bed been boy brother but by call(ed) came can’t could did do don’t door down first from girl good got had half has have help her here him his home house how if jump just last laugh little live(d) love made make man many may more much must name new next night not now off old once or our out over people pull push put ran saw school seen should sister so some take than that their them then there these three time too took tree two us very want water way were what when where who will with would your Monday Tuesday Wednesday Thursday Friday Saturday Sunday January February March April May June July August September October November December red yellow blue green orange pink purple black white brown Medium frequency words ask asked began being brought can’t change coming didn’t does don’t found goes gone heard I’m jumped knew know leave might opened show started stopped think thought told tries turned used walk walked
    [Show full text]