WHAT IS THE MEANING OF NEGATIVE MODULATION IN AM MO0DULATIO

 

If your talking about a TV signal, the lower the carrier amplitude the lighter the picture, the bigger the carrier amplitude the darker the picture, this is to reduce noise spots,.

 

All voltages are relative. With AM modulation, it is most convenient to reference the signal voltage against the center, mean level, and to call that 0V. That requires half of the signal to be at a negative voltage.

Is that what you were asking?

 

positive and negative modulation are terms usually used in cb radio language, meaning that a watt meter goes up or down with modulation. 100 % modulation has the same amount in both dirrections.

 

WHAT IS THE MEANING OF NEGATIVE MODULATION IN AM MO0DULATIO

And be aware, you can never exceed 100% negative modulation, while it's possible to have much more than 100% modulation, if using an asymmetrical audio signal. A.M. broadcasting allows 130% positive modulation peaks (in the U.S.)

 

I mean when we say that there are three frequencies that is f+f1 and f-f1 which is ploted in negative axis

 

Neither you're talking about SSB modulation, Upper and Lower carriers are just separated by about 10khz bandgap.

 

When you superimpose two sine waves, the carrier and the modulation, they beat, or form interference patterns, and you will find power appearing at the frequency of the carrier plus the modulation frequency, and at the carrier minus the modulation.

If your prefer math, go see this. A more visual description here.