Is the transmission in comm. always analog ?

[desperado1]

I recently read that both in analog communications and digital communications, the transmission is always analog. Is it correct ? Then what abt PCM, ADPCM ,PWM. they are digital. Can't they be transmitted ?

 

[dipnirvana]

well digital transmission is there like RS232, RS485 etc . there are lotz of other example , too

 

[hamdard]

Transmission may be for both types analog and digital.
In analog transmission, the data is analog.
In digital transmission, the data is digital and processing is digital as well.

 

[Communications_Engineer]

Analog is only due to necessity when our channel is unable to carry digital information. Otherwise we always prefer digital

Like a wireless channel is not good enough to carry digital so analog is used while your Ethernet cables are able to carry digital data so we use digital there.

 

[desperado1]

Thanks Communications_Engineer...........but why a wireless channel is not good enough to carry digital data....?

 

[Communications_Engineer]

because digital data is on/off so imagine your transmitter turning on/off every symbol time.

Secondly, the power in the digital signal is very less it would not be able to travel a large distance

Third and perhaps the most important, digital data is base band in nature meaning it would want to occupy 'all' frequencies..... of course no one would allow that

 

[FvM]

in analog communications and digital communications, the transmission is always analog

To my opinion, this simple remark is containing more truth than some of the following explanations in this thread.

An analog signal is continuous in amplitude and time. A digital signal is always amplitude-discrete, but (also depending on your definition) may be time-continuous or discrete. E. g. PCM is time-discrete, PWM, if generated by an analog modulator, can be understood as time continuous.

An ethernet physical layer signal has obviuosly analog properties, particularly a complex analog waveform altough it's representing digital data.

Looking at wireless transmission, that is apparently addressed with the original question, I don't see a basic difference to wired transmission. The carrier is also an analog signal, but it can of course represent a digital signal. Simple modulation methods as BPSK are illustrating this obvious fact.