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Radio Frequency Bands Source: J.Jayastree (132242601007) M.Tech(COS) The Electromagnetic Spectrum  Frequency Band Is a specific range of frequencies in the radio frequency (RF) spectrum. Radio frequency (RF) is a rate of oscillation in the range of aroun...

Radio Frequency Bands Source: J.Jayastree (132242601007) M.Tech(COS) The Electromagnetic Spectrum  Frequency Band Is a specific range of frequencies in the radio frequency (RF) spectrum. Radio frequency (RF) is a rate of oscillation in the range of around 3kHz to 300 GHz, which corresponds to the frequency of radio waves and the alternating current which carry signals.  Very Low Frequency ranges from 3 KHz to 30 KHz. Wavelength ranges from 10 to 100 km. Low Frequency ranges from 30KHz – 300 KHz. also known as kilometer band or kilometer wave. Medium Frequency (MF) ranges from 300KHz to 3MHz it follows ground wave and sky wave propagation High Frequency (HF) ranges from 3MHz to 30MHz. Wavelength ranges from 1 to 10decameters. Very High Frequency (VHF) Very High Frequency ranges from 30MHz to 300MHz. Wavelength ranges from 1 to 10 meters.  Ultra High Frequency (UHF) ranges from 300MHz and 3GHz. Also known as decimeter band or decimeter wave. Super High Frequency (SHF) ranges from 3GHz to 30GHz. also known as centimeter band or centimeter wave. Wavelength ranges from 1 to 10cms. Extremely High Frequency (EHF) ranges from 30 to 300GHz. also known as millimeter band or millimeter wave Wavelength ranges from 10 to 100mm. Frequency Bands Frequency Bands  Limitations of a Communication System  BANDWIDTH - a range of frequencies within a given band, in particular that used for transmitting a signal. for AM System --- 30kHz for FM System --- 200 kHz for TV System --- 6MHz  ELECTRICAL NOISE A. External Noise a. Man-made – noise from external sources such as powerlines and ignition systems. b. Atmospheric - radio noise caused by natural atmospheric processes. c. Solar Noise - noise that originates from the Sun. Under normal conditions there is constant radiation from the Sun due to its high temperature. Electrical disturbances such as corona discharges, as well as sunspots can produce additional noise. d. Cosmic Noise - is experienced at frequencies above about 15 MHz when highly directional antennas are pointed toward the sun or to certain other regions of the sky such as the center of the Milky Way Galaxy. B. Internal Noise a. Thermal Noise – Due to random motion of electrons. – It is found everywhere (resistors, speakers, microphones, antennas. – It is directly proportional to absolute temperature. – Also called Johnsons Noise or White noise - frequency independent up to 1013 Hz.  Thermal Noise Modeling The noise power is represented by the rms value: According to J. B. Johnson,  b. Shot Noise - is due to the random arrivals of electrons at the potential barrier of forward biased P/N junctions. - It is always associated the a dc current flow in diodes and BJTs.  Shot Noise Modeling The noise amplitude is represented by the rms value: in = 2qI D f −19 where q = 1.6 10 C  Sample Problem Determine the noise power and noise voltage generated by 3-1kohm resistors in (a) series (b) parallel operating at 100Mhz bandwidth and a temperature of 27 OC (c) at the same bandwidth, determine the shot noise produced by a diode with a dynamic resistance of 26Ω.  Modulation & Demodulation Modulation - is a process of impressing a low frequency signal(audio signal) onto a high frequency signal(carrier signal) for effective transmission. Demodulation – is a process of extracting a low frequency signal(audio signal) from a high frequency signal(carrier signal). Why is there a need for Modulation-Demodulation process? a. Length of Antenna b. Narrow Banding of Signal c. Frequency Multiplexing d. Effective Radiated Power Equation of the Carrier Signal eC = Em Sin (ωt + θ ) where Em - amplitude ωt - angular frequency θ - phase angle  If the amplitude of the carrier signal is varied, Amplitude Modulation ( AM ) audio signal carrier signal AM signal Source: https://www.physics-and-radio-electronics.com/blog/amplitude-modulation/  If the frequency of the carrier signal is varied, Frequency Modulation ( FM ) audio signal carrier signal FM signal Source: https://www.physics-and-radio-electronics.com/blog/frequency-modulation/  If the phase angle of the carrier signal is varied, Phase Modulation ( PM ) audio signal carrier signal PM signal Source: https://www.physics-and-radio-electronics.com/blog/amplitude-modulation/ Block Diagram of Basic Communication System Noise ELEMENTS OF BASIC COMMUNICATION SYSTEM 1.Input transducer. 2.Transmitter. 3.Communication channel. 4.Receiver. 5.Output transducer.  1. INPUT TRANSDUCER The information in the form of sounds, picture signal can not be transmitted as it is first it has to be connected into a suitable electrical signal the input transducer done this job.  2. Transmitter The function of transmitter block is to convert the electrical signals to the information of a suitable form. The transmitter consists of the electronic circuit such as amplifier oscillator & power amplifier.  3. Communication Channel The communication channel is the medium used for transmission of signal from one place to another. The communication medium can be conducting optical fiber depending two types of communication medium which exist they are. (i)wire communication (II)wireless communication  Noise Noise is an unwanted electrical signal which gets added to the transmitted signal when it is travelling towards the receiver the noise can be natural or man made. The source of natural noise one lighting or radiation from the sum and stars etc. the man made noise includes the noise produce by electrical ignition system of the automobile machine etc.  4. RECEIVER The reception is exactly the opposite process of transmission demodulation and connected into a suitable form the receiver consists of electronic circuit line oscillator amplifier etc.  5. OUTPUT TRANSDUCER It connects the electrical signal at the output of the receiver back to the original form that is sound, picture, video etc.