Define Pulse Code Modulation.?
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pulse-code modulation - \na system of radio transmission in which successive electromagnetic waves of short duration are sampled periodically, quantized, and transmitted by code. \nEx. The result was the rapid development of pulse-code modulation ... as a rival to amplitude modulation (AM) and frequency modulation (FM)
180045
93320 Medicine Doppler echocardiography, pulsed wave and/or continuous wave with spectral display (list separately in addition to codes for echocardiographic imaging 93307, 93308, 93312, 93314, 93315, 93316, 93317, 93350); complete.  $87.81 \n93321 Medicine Doppler echocardiography, pulsed wave and/or continuous wave with spectral display (list separately in addition to codes for echocardiographic imaging 93307, 93308, 93312, 93314, 93315, 93316, 93317, 93350); follow-up or limited study.  $50.13 \n93325 Medicine Doppler color flow velocity mapping (list separately in addition to code for echocardiography 76825, 76826, 76827, 76828, 93307, 93308, 93312, 93314, 93320, 93321, 93350).  $104.96 \n\nFound this on a website when I searched "Doppler". They are CPT-4 codes.
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modem\n(MOdulator-DEModulator) Until the late 1990s, the term stood for a device that allowed a computer or terminal to transmit data over a standard dial-up telephone line. Since the advent of high-speed cable and DSL connections, modem may refer to devices for low-speed dial-up or high-speed broadband.\n\nThis definition pertains only to dial-up modems, which convert digital pulses from the computer to audio tones that an analog telephone line is set up to handle and vice versa. V.92 is the last dial-up standard, providing a data rate of 56 Kbps (see V.92). For high-speed broadband modems, see cable modem, DSL and cellular modem.
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the ground is being use as one line and a wire hangs on air to the other with batteries connected to the circuit. either end has switching device (key) and magnetic sounder. when an operator press the key (short and long) several times with different pressing lenght, this represent letters and the other end operator hears the long and short combination. he know about the code (Moorse Code) so he can spell the message
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there will stretching to the string, and the amplitude and frequency will be tranmitted....but the cycles wont be at light speed...so they wont allow for instantaneous communication.  Now if the cable was fiberoptic...and pulses were transmitted...hmm
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go to http://ucp.ece.gatech.edu/content/3042/3042_WA2_fall03.pdf#search='pulse%20width%20modulator%20with%20555%20timer%20and%20LM311%20comparator\n\nor\nwww.colorado.edu/~ecn4618/lab2.pdf\n\nI hope this helps you somewhat.
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sender , message , channel , receiver
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I don't believe there is modulation within CDMA.  You are confusing yourself.\n\nCode division multiple access (CDMA) is a form of multiplexing (not a modulation scheme) and a method of multiple access that does not divide up the channel by time (as in TDMA), or frequency (as in FDMA), but instead encodes data with a special code associated with each channel and uses the constructive interference properties of the special codes to perform the multiplexing. CDMA also refers to digital cellular telephony systems that make use of this multiple access scheme, such as those pioneered by Qualcomm, or W-CDMA.
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Electromagnetic Pulse (EMP), the short, powerful electromagnetic field produced by atmospheric ionization during the explosion of a nuclear weapon. An EMP may extend long distances, depending on the height of the burst, and can severely damage modern electronic equipment, including communications systems. For this reason EMP is a significant aspect of national security in planning nuclear-war strategies.
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http://en.wikipedia.org/wiki/Modulation_index
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it is a unit regarding telephone signals
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Here are two web sites with the code listings:\nhttp://www.radiolabs.com/police-codes.html\nhttp://www.tracone.com/police_scanner/police-codes.htm\n\nAlso, next time you're looking for something like this, I recommend http://www.ixquick.com  It's a great meta search engine.
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In general, a transmitted signal can be described as s=A*cos(omega + phi).  In AM modulation, you change the amplitude "A".  In FM, you modify the fundamental frequency, omega.  In PM, you modify the phase, phi.\n\nPhase Modulation is heavily used in digital communications.  Modems, satellite TV, GPS, and Wireless LANs (802.11a/b/g) all use variants of binary and quadrature phase shift keying.
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Let's try a slightly different explanation.  A Decoder is used to change a pattern of voltage pulses or digital signals into a different pattern with a smaller pulse width.  Generally, a Decoder and Coder pair are used to place data from different sources into the same circuit.  The decoder simply breaks out these signals to multiple circuits.\n\nA mux/demux pair performs a similar task for analog or sinusoidal signals.  Generally, the digital signals coming in to a multiplexer will have a specific frequency assigned to it the multiplexer mixes these different frequencies together into a composite signal.  On the other end the signals reach a demux, or de-multiplexer.  Here the different frequencies are broken out into different digital signals.\n\nDave Cooke
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Amplitude modulated radio radiation is the result of a disturbance in space. The signal travel in all directions and can be received at a wide range of location. However Am transmission is very suceptible to noise. Hence a lack of fidelity.\n\nFrequence modulation is really Power modulation rather than amplitude.Since the signal can vary as a fucntion of frequency there is better clarity in the reception. But the .Television signal Use the same principle as FM.Hower since the wave lenght of the signal carrier is much shorter. Hence they are more directional.The transmison cannot be as wide spread as the long wave in Am.
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aefhiklmqtwxy\nbcdgjnoprsuvz
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Are you asking for the mathematical representation of a frequency modulated signal (FM)?  If so, it is:\n\nXc(t)=Ac*cos[omegaC*t + fDelta*X(t)]\n\nWhere t is time, Xc is the the modulated carrier, Ac is the amplitude of the carrier, omegaC is the frequency of the carrier (in radians per second), fDelta is the modulation index (amount of frequency change allowed), and X(t) is the message.\n\nSee chapter 5 of reference in "source(s)".