A question about digital-modulated signal amplification

[BigDogBear]

Why the non-constant envelope modulated signal can not be amplified by the non-linear amplifier?

 

[alex_vettoriale]

Hi...
One non constant envelope modulated signal has information into its phase and amplitude (AM).
So if u use a non linear amp, like a class C amplifier
that works in saturation, the signal's envelope will be flatted and the information that was on the envelope lost. Another problem is that u will have in band intermodulation of your signal, losing again information. For this reasons u will need linear amplifiers, losing in efficiency vs non linear amps.
Regards
Alex_vettoriale

 

[springf2000]

because the AM-AM AND AM-PM characterstic of the non-linear shall corrupt the modulated waveform, certainly corrupt the modulated information!

 

[johnseven]

Hi...
One non constant envelope modulated signal has information into its phase and amplitude (AM).
So if u use a non linear amp, like a class C amplifier
that works in saturation, the signal's envelope will be flatted and the information that was on the envelope lost. Another problem is that u will have in band intermodulation of your signal, losing again information. For this reasons u will need linear amplifiers, losing in efficiency vs non linear amps.
Regards
Alex_vettoriale

Great explanation Alex.

My two cents:
Many young bright students of the art of electrical engineering have been ignoring the "ANALOG" world, equating it with old fashioned, primitive, passe', etc.
Not so fast digital geniuses! Back to physical basics.

The spectrum of usable frequencies in the real world is "de-facto" analog!
And it's FINITE!
In order to transmit signals through space (air) You have to decide about bandwidth, speed and center frequency. There's no room here to write about the theory of communications. Spend a couple of hours reading about the basic principles available in thousands of books. Want it digested? Read the ARRL "Radio Amateurs Handbook". Easy and smooth.
A little technical about amplifying and transmitting digital signals. One has to use modulation methods like FSK, AFSK, PSK, and many more.
i.e: digital signals have to be transformed into analog to be processed for "air" transmission. Then these signals can be de-mofied back to digital.

Keep on. Electronics is fun!

J7