communication

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Please be more specific.

Are you talking about AM or FM?

Then we could talk about DSB SSB, SSBSC, PM, PFM, FSK. . .

Have you searched Google and Wikipedia?
 
Hero999 said:
Please be more specific.

Are you talking about AM or FM?

Then we could talk about DSB SSB, SSBSC, PM, PFM, FSK. . .

Have you searched Google and Wikipedia?
Click to expand...

As one of the dots kept by Hero999, I would add DSC (for DSB SC)

Now a new term like OFDM has come in for Digital Radio Mondiale (DRM).
 
virajtolia said:
hello friends..........
pls i want clear explanation of modulations. pls help me.
Click to expand...
This is a gross oversimplification, but think about it as multiplying two signals together. To see what happens, take two sinusoids of different frequencises and multiply them together. Then ask yourself, "What frequencises are present in the product waveform". There are four of them, now your homework is to tell us what they are. The tigonometry is moderately tough, but you asked the question.

Code: 
sin(at) * sin(bt) = ?
for frequencies a, b such that a != b
 
yes, OFDM, DFSS, and QAM are important too.

AM - the amplitude of a high frequency signal changes. modulation can have a carrier (AM), no carrier (DSB-SC), and may remove a redundent sideband (SSC-SC)
FM - the frequency of a high frequency signal changes (PM, the phase changes)
QAM - both amplitude and frequency change.
OFDM - the signal is transmitted on multiple carriers (maybe at the same time, maybe not)
DFSS - and it changes carriers in a predictable pattern.

ASK/FSK/PSK are AM, FM, and PM used with digital signals.
 
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