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Analog Communications. Overview. Communication systems Analog Modulation AM FM Digital Modulation ASK FSK Modems. Communication systems. The block diagram on the top shows the blocks common to all communication systems. Digital. Analog.
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Simple Communications

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Overview Communication frameworks Analog Modulation AM FM Digital Modulation ASK FSK Modems

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Communication frameworks The square outline on the top demonstrates the pieces normal to all correspondence frameworks Digital Analog

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Remember the segments of an interchanges framework: Input transducer: The gadget that changes over a physical flag from source to an electrical, mechanical or electromagnetic flag more reasonable for conveying Transmitter: The gadget that sends the transduced flag Transmission channel: The physical medium on which the flag is conveyed Receiver: The gadget that recoups the transmitted flag from the channel Output transducer: The gadget that changes over the got motion once more into a valuable amount

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Analog Modulation The motivation behind a correspondence framework is to transmit data signals (baseband signals) through a correspondence channel The term baseband is utilized to assign the band of frequencies speaking to the first flag as conveyed by the info transducer For instance, the voice motion from an amplifier is a baseband flag, and contains frequencies in the scope of 0-3000 Hz The "welcome" wave is a baseband flag:

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Since this baseband flag must be transmitted through a correspondence channel, for example, air utilizing electromagnetic waves, a proper technique is expected to move the scope of baseband frequencies to other recurrence ranges appropriate for transmission, and a relating shift back to the first recurrence run after gathering. This is known as the procedure of regulation and demodulation Remember the radio range: For instance, an AM radio framework transmits electromagnetic waves with frequencies of around a couple of hundred kHz (MF band) The FM radio framework must work with frequencies in the scope of 88-108 MHz (VHF band) AM radio FM radio/TV

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Since the baseband flag contains frequencies in the sound recurrence run (3 kHz), some type of recurrence band moving must be utilized for the radio framework to work attractively This procedure is expert by a gadget called a modulator The transmitter hinder in any interchanges framework contains the modulator gadget The recipient obstruct in any correspondences framework contains the demodulator gadget The modulator tweaks a transporter wave (the electromagnetic wave) which has a recurrence that is chosen from a suitable band in the radio range For instance, the recurrence of a bearer wave for FM can be looked over the VHF band of the radio range For AM, the recurrence of the transporter wave might be been around a couple of hundred kHz (from the MF band of the radio range) The demodulator separates the first baseband motion from the got adjusted flag To Summarize: Modulation is the way toward awing a low-recurrence data flag (baseband flag )onto a higher recurrence bearer flag Modulation is done to convey data motions up to the Radio Frequency (or higher) flag

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Basic simple interchanges framework Baseband flag (electrical flag) EM waves (balanced flag) Transmitter Input transducer Transmission Channel Modulator EM waves (regulated flag) Carrier Baseband flag (electrical flag) Receiver Output transducer Demodulator

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Types of Analog Modulation Amplitude Modulation (AM) Amplitude balance is the way toward changing the abundancy of a transporter wave in extent to the sufficiency of a baseband flag. The recurrence of the bearer stays consistent Frequency Modulation (FM) Frequency regulation is the way toward changing the recurrence of a transporter wave in extent to the adequacy of a baseband flag. The plentifulness of the bearer stays consistent Phase Modulation (PM) Another type of simple tweak system which we won\'t talk about

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Amplitude Modulation

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Amplitude Modulation Uses a higher recurrence transporter Most proficient utilization of recurrence Time and Frequency Domain Susceptible to Noise

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Sine Wave Peak Amplitude (A) greatest quality of flag volts Frequency (f) Rate of progress of flag Hertz (Hz) or cycles every second Period = time for one reiteration (T) T = 1/f Phase ( ) Relative position in time, from 0-2*pi General Sine wave

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S(t) = A c (1 + K a m(t))cos(2f c t) Where K a will be a steady. m(t) is the baseband message. For a sound flag, the range of m(t) would ordinarily be in the scope of 300 Hz - 3 kHz. f c is the transporter recurrence m(t) = A m cos(2f m t) Where f c >> f m .

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Varying Sine Waves

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Higher Frequency Carrier Signal time Carrier time

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Higher Frequency Carrier Power Spectral Density watts Carrier Signal recurrence Baseband

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Time Domain Signal time Carrier time

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Time Domain Continued

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Amplitude Modulation Carrier wave Baseband flag Modulated wave Amplitude changing recurrence consistent

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Some AM Waveforms

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Detection of Signal time

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Frequency Domain Unmodulated watts Carrier Signal recurrence Baseband watts Modulated Carrier Signal recurrence Baseband

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The AM Waveform The three parts that frame the AM waveform are recorded underneath: 1. The lower-side recurrence (fc - fi) 2. The transporter recurrence (fc) 3. The upper-side recurrence (fc + fi) If a radio flag of recurrence with1000KHz is blended with a sound flag of 1 KHz the yield will be A flag at 1000 KHz (Carrier wave) A flag at 1001 KHz (upper sideband) A flag at 999 KHz (bring down sideband)

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Upper and Lower Sidebands

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Upper and Lower Sidebands In many frameworks the insight flag is a perplexing waveform containing segments from around 200Hz to 3KHz. On the off chance that this mind boggling waveform is utilized to adjust the bearer there would be an entire band of side frequencies. The band of frequencies over the transporter is term the upper sideband. The band of frequencies underneath the bearer is known as the lower sideband.

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Example A 1.4MHz transporter is tweaked by a music flag that has recurrence parts from 20Hz to 10kHz. Decide the scope of frequencies created for the upper and lower sidebands.

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Percentage Modulation Determination

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Example 2 An unmodulated bearer is 300Vp-p. Compute %m when its greatest p-p esteem comes to: a. 400 b. 500 c. 600

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Answers 33.3% b. 66.7% c. 100%

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Points to be Remembered Amplitude adjustment is the way toward differing the sufficiency of a bearer wave in extent to the plentifulness of a baseband flag. The recurrence of the transporter stays consistent The capacity of the bearer in AM is basically to give a flag to heterodyne (blend) with the adjusted sound, to change over all the AF segments to a higher recurrence. The data transfer capacity of an AM flag is equivalent to double the most elevated freq. [ In business AM communicate tx\'s the freq of the regulating sound is allowed to be as high as 4.5 KHz, and since a twofold side framework is utilized , business stations subsequently have a transmission capacity of 9 KHz] The transfer speed does not rely on upon the force of the balancing signal.

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