# Why only odd harmonics after signal is amplified? *Plots inside*

Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve.

I make an input signal and the power of this will saturate the amplifier.

So the details of the amplifier is that I have a a transfer curve for power in and power out. I also have a transfer curve for power in and phase deviation. Then I make a phasor that amplifies each point on the signal to do AM and PM of the amplifier.

This is basically how I do it

My input signal, x(t), is the sum of two sine waves


For each point on the transfer curve above I apply Amplitude and Phase modulation by using this array

modulating_phasor[] = (power_out / power_in) * exp(i*phase_deviation)


Then I look at my input signal and lookup where its value matches the input power of the transfer curve and use that location in the modulating_phasor array

output_signal[] = x(t) * modulating_phasor[location]


This makes the output signal complex array so I take the absolute value and for parts that should be negative, I multiply that location on by -1 by finding the correct location on input signal.

Now this is my output and no matter what my input level on my signal is, I always get odd harmonics!

• You are leaving out the details of the amplifier -- the one that's leads to the note "Amplifier Saturat..." (presumably "Saturation") in the upper right plot on your set of four. The amplifier is clearly distorting with a function that is odd-symmetric, which leads to odd harmonics. May 23, 2019 at 15:14
• She is asking why only odd harmonics, not even harmonics also. Any symmetrical wave will only produce odd harmonics, but why? Symmetrical defined in this context as one period can be reversed in time and still be the same (or inverted). May 23, 2019 at 15:19
• So the details of the amplifier is that I have a a transfer curve for power in and power out. I also have a transfer curve for power in and phase deviation. Then I make a phasor that amplifies each point on the signal to do AM and PM of the amplifier. May 23, 2019 at 15:19
• Try adding a DC offset to the amplifier input (I assume its response goes to 0Hz)...then watch those even harmonics appear. May 23, 2019 at 15:35
• Looks to me like your amplifier is saturating, which makes its output look a lot more like a square wave, which contains only odd harmonics (and quite a lot of them). May 23, 2019 at 15:40