ESAT Module 1: Wave Propagation, Transmission Line & Antennas PDF

ESAT MODULE 1: Wave Propagation, Transmission Line and Antennas Radiation of Electromagnetic Energy - electromagnetic radiation from an antenna Conventional Antenna- a conductor, or system...

ESAT MODULE 1: Wave Propagation, Transmission Line and Antennas Radiation of Electromagnetic Energy - electromagnetic radiation from an antenna Conventional Antenna- a conductor, or system is made up of two components, the E field of conductors, that radiates or intercepts and the H field electromagnetic wave energy - The two fields occur 90 degrees out of Factors to Consider for Antenna phase with each other - height of the radiator above the earth - These fields add and produce a single - the conductivity of the earth below it, electromagnetic field - shape and dimensions of the antenna - as the wave advances, the energy spreads Classifications of Antennas out over a greater area and, at any given Hertz (half-wave) Antennas/ Dipole/ point, decreases as the distance Doublet increases. - installed some distance above the ground Standing Wave Current- a maximum and are positioned to radiate either movement of electrons is in the center of the vertically or horizontally antenna at all times; therefore, the center of the - generally used for frequencies above 2 antenna is at a low impedance megahertz Loops- points of high current and high voltage - each half of the wire is 1/4 wavelength of Nodes- points of minimum current and minimum the output voltage MARCONI (quarter-wave) Antennas - operate with one end grounded and are Antenna Characteristics Reciprocity- property of interchangeability of the mounted perpendicular to the Earth or to same antenna for transmitting and receiving a surface acting as a ground electromagnetic field - used for frequencies below 2 megahertz Gain- ratio between the amount of energy and may be used at higher frequencies in propagated in these directions compared to the certain applications. energy that would be propagated if the antenna Parts of Antenna System were not directional 1. Coupling Device- connects the - When a transmitting antenna with a transmitter to the feeder certain gain is used as a receiving 2. Feeder- transmission line that carries antenna, it will also have the same gain energy to the antenna for receiving. 3. Antenna- radiates this energy into Polarization- The electric field determines the space direction of polarization of the wave Factors That Determine the Type, Size, and - Vertical- the electric lines of force lie in a Shape of the Antenna vertical direction 1. Frequency of operation of the transmitter - Horizontal- the electric lines of force lie 2. Amount of power to be radiated in a horizontal direction 3. General direction of the receiving set - Circular- the electric lines of force Current and Voltage Distribution on an rotating through 360 degrees with every Antenna cycle of RF energy Laws and Principles of Radiation of Polarization Requirements for Various Electromagnetic Energy Frequencies 1. MOVING ELECTRIC FIELD Ground-wave transmission CREATES a Magnetic (H) FIELD - used at medium and low frequencies 2. MOVING Magnetic FIELD -uses vertical polarization because of its CREATES an ELECTRIC (E) electric lines of force that are parallel to and touch FIELD the earth and have a minimum attenuation o these two fields will be in phase Sky-wave transmission and perpendicular to each other at - used at high frequencies any given time Either horizontal or vertical polarization because it arrives at the receiving antenna elliptically polarized Radiation Resistance - In the case of radiation, R is an assumed resistance; if this resistance were actually present, it would dissipate the same amount of power that the antenna takes to radiate the energy - antenna in free space, radiation resistance is 73 ohms - antenna located over a ground plane, resistance from 0 to approximately 100 ohms - most half-wave wire antennas, the radiation resistance is about 65 ohms - antennas constructed of rod or tubing, 55 and 600 ohms Radiation Types and Patterns Isotropic Radiation- radiate energy equally in all directions Rectangular-Coordinate Pattern- the lines used to plot the point form a rectangle Polar-Coordinate Pattern- can immediately see the direction and strength of radiation put out by the source. Anisotropic Radiation- emit (radiate) stronger radiation in one direction than in another ex. Flashlight LUMPED-Impedance TUNING or LOADING- To change the electrical length, you can insert either an inductor or a capacitor in series with the antenna ESAT MODULE 1: MCQS director Which of the following is not a part of a complete antenna system? characteristic impedance of the not a factor in determining the type, size, and shape of the antenna transmission line used antenna reciprocity property of interchangeability of the same antenna for transmitting and receiving loop points of high current and high voltage on an antenna node points of minimum current and minimum voltage on an antenna ratio between the amounts of energy propagated in these directions compared to the energy antenna gain that would be propagated if the antenna were not directional vertical antennas type of antenna can be used if communications must take place from a moving vehicle horizontal type of polarization does VHF and UHF transmission use vertical polarization does MF and HF transmission use isotropic radiation radiation that radiate energy equally in all direction assumed resistance that would dissipate the same amount of power that the antenna takes to radiation resistance radiate the energy current loop Radiation resistance is always measured at 73 ohms radiation resistance of an antenna in free space rigor mortis NOT an indication that a person has received a severe electric shock radiation pattern plot of the radiated energy from an antenna bandwidth range of frequencies over which the antenna can operate correctly directivity to focus energy in a particular direction when transmitting, null a zone in which the effective radiated power is at a minimum has a high impedance not true about the grounded end of the quarter-wave antenna reduce losses in the ground in the purpose of a ground screen in vertical quarter-wave antennas immediate vicinity of the antenna counterpoise same purpose as the ground screen, but it is usually elevated above the earth It is composed of a series of conductors arranged in a radial physical arrangement of a ground screen pattern and buried 1 to 2 feet below the ground. ordinary half-wave antenna that has one or more additional conductors connected across its folded dipole ends element of an antenna array that similar to the dipole and is connected directly to the driven transmission line. element of antenna array that is not connected to the transmission line but located near the parasitic driven element from which it gets its power as close as possible to A low pass filter in an HF station is most effective when connected the transceiver output as close as possible to the linear amplifier A low pass filter in an HF station is most effective when connected output In designing an HF station, which component would you use to reduce the effects of harmonic Low pass filter radiation  component in an HF station is the most useful for determining the effectiveness of the antenna SWR bridge system In HF, which component would normally be connected closest to the antenna, antenna tuner Antenna switch and dummy load in HF, which component would be used to match impedances between the transceiver and Antenna tuner antenna Dummy load In an HF station, which component is temporarily connected in the tuning process most antennas when operating below 14 In an HF station, the antenna tuner is usually used for matching the transceiver with MHz with most antennas when operating below In an HF Station, the antenna tuner is commonly used 14 MHz microphone In a frequency modulation transmitter, the input to the speech amplifier is connected to the speech amplifier In a frequency modulation transmitter, the microphone is connected to the modulator In FMT, the is in between the speech amplifier and the oscillator oscillator In FMT, the is located between the modulator and the frequency multiplier frequency multiplier In FMT, the is located between the oscillator and the power amplifier power amplifier In FMT, the is located between the frequency multiplier and the antenna antenna In FMT, the power amplifier output is connected to the In a frequency modulation receiver, the is connected to the input of the radio frequency antenna amplifier. radio frequency In FMR, the is in between the antenna and the mixer amplifier mixer In FMR, the output of the high frequency oscillator is fed to the high frequency In FMR, the output of the is connected to the mixer oscillator filter In FMR, the is in between the mixer and the intermediate frequency amplifier 1 GHz The microwave frequency range is considered to start at below the microwave The UHF range is: range the shape of the The dominant mode of a waveguide depends on: waveguide TE10 The dominant mode of a rectangular waveguide is TE11 The dominant mode of a circular waveguide is of its circular symmetry Circular waveguides use TM 01 mode because The threshold point in FM detection occurs if the signal power is nearly _____ times the noise ten power Amplitude Modulation AM stands for: the baseband signal The "envelope" of an AM signal is due to: m = Va / Vc If the audio Va sin(ωat) modulates the carrier Vc sin(ω ct), then the modulation index, m, is Distortion and Splatter Overmodulation causes m = (Emax – Emin) / The peak voltage of an AM signal goes from Emax to Emin. The modulation index, m, is (Emax + Emin) half the carrier power At 100% modulation, the total sideband power is: 10 kHz If a 5-kHz signal modulates a 1-MHz carrier, the bandwidth of the AM signal will be Louder audio, SNR increases, RF signal If an AM radio station increases its modulation index, you would expect increases Time-domain and Frequency-domain The modulation index can be derived from signal incompatibility with The main problem in using quadrature AM would be: ordinary AM radios More efficient, requires more complex As compared to plain AM, SSB AM demodulator circuit and less bandwidth suppressed-carrier The SC in SSB SC stands for Peak Envelope Power PEP stands for: If an SSB transmitter radiates 1000 watts at peak modulation, what will it radiate with no 0 watts modulation commercial AM stations have a narrow Music on AM radio stations is "low-fidelity" because: bandwidth Audio, video and The type of information that can be sent using AM is digital data Two tones modulate an AM carrier. One tone causes a modulation index of m 1 and the other sqrt(m12 + m22) tone causes a modulation index of m2. The total modulation index is Be set to USB mode and To demodulate a USB SSB signal, the receiver must reinsert the carrier If the plate supply voltage for a plate modulated class C amplifier is V, the maximum plate- 2V cathode voltage could be almost as high as linear devices In a low-level AM system, amplifiers following the modulated stage must be If the carrier of a 100 percent modulated AM wave is suppressed, the percentage power saving 66.66 will be prevent excessive grid Leak type bias is used in a plate modulated class C amplifier to current grid modulated class C The output stage of a television transmitter is most likely to be a amplifier transmission line This is defined as a device designed to guide electrical energy from one point to another characteristic ratio of voltage to current at any point on that transmission line would be some particular impedance value of impedance This line consists of two wires that are generally spaced from 2 to 6 inches apart by insulating two-wire open line spacers twin lead used to connect a television receiving antenna to a home television set twisted pair consists of two insulated wires twisted together to form a flexible line without the use of spacer shielded pair parallel conductors separated from each other and surrounded by a solid dielectric Whenever current flows through one of these conductors, some energy is dissipated in the copper loss form of heat. This heat loss is a power loss and referred to as A loss in transmission line that results from the heating effect on the dielectric material dielectric loss between the conductors A loss in transmission line that occurs when the electromagnetic field about a conductor cuts induction loss through any nearby metallic object  A loss in transmission line that occurs because some magnetic lines of force about a conductor radiation loss do not return to the conductor when the cycle alternates its physical length is short compared to a λ/4 A transmission line is considered to be electrically short when of the energy it is to carry Voltage is reflected without change in What happens when a dc voltage is sent through an open-ended transmission line polarity, amplitude, or shape Current is reflected with opposite polarity In an open-ended transmission line and without change in amplitude or shape The reflected voltage has the opposite polarity but the same In a short-circuited transmission line amplitude as the incident wave The reflected current has the same polarity and the same What can you say about the reflected current in a short-circuited transmission line amplitude as the incident current. nonresonant line A line that is either infinitely long or terminated in its characteristic impedance Resonant lines are also Which of the following is NOT true for resonant lines called as flat lines voltage is minimum and current is On an open-ended resonant line, at all odd λ/4 points maximum voltage is maximum and current is On an open-ended resonant line, at all even λ/4 points minimum this refers to the measurement of maximum voltage (current) to minimum voltage (current) on standing wave ratio a transmission line and measures the perfection of the termination of the line. This refers to a logarithmic ratio measured in dB that compares the power reflected by the return loss antenna to the power that is fed into the antenna from the transmission line. This refers to a miniature quick connect / disconnect connector that features two bayonet lugs BNC connector on the female connector, and mating is achieved with only a quarter turn of the coupling nut. These are precision, subminiature units that provide excellent electrical performance up to 18 SMA connector GHz. These high-performance connectors are compact in size and mechanically have outstanding durability.