...... I thought that a sine wave had only one frequency, the fundamental.

Not true. A sine wave is constructed using the even harmonics of the fundamental frequency. (I am trying to find some reference material that does not delve in to fast Fourier transforms but even harmonics are always present.)

 

(Note: Les, a sine wave has only one frequency unless it is full wave rectified).

Hi, addressing the main questions here,

Just to note, when you take two sine waves and multiply them together and they are both the same that is effectively squaring the sine wave so we get as output:
1/2-cos(2*w*t)/2

which contains a DC component and an AC component at twice the input frequency and half the amplitude. After removing the DC component we would be left with:
cos(2*w*t)/2
so it would be double the frequency just at half the original amplitude.

Full wave rectifying a sine wave also produces the 2nd harmonic as well as other harmonics as well as DC of about 0.6 in amplitude.
The 2nd harmonic is about 42 percent of the original amplitude so it's a sine with amplitude 0.42 of the original.
The next harmonic is the 4th, and that is about 8 percent of the original so it's about 5 times less than the 2nd.
The next is the 6th, and that is about 4 percent of the original.
We also have to look at the output frequencies too though.
The 2nd will be around 200MHz, and the 4th around 400MHz, and the 6th around 600MHz as a min.
These frequencies will all be attenuated naturally by at least some degree, so there is a chance that the frequency content will be clean enough without any more filtering.

Just a couple things to note.

 

OK, theoretically, you could have a sine wave that had no energy except at the fundamental frequency, but not in reality. Connect the best ultra pure signal sources to a spectrum analyzer and you will see even harmonics.

My question stands, why do you need a sine wave?

 

I'll bet 10 op amps that your last question is not answered by the OP (or, if it is addressed, the answer won't make sense).

I match your 10 and raise you another ten op-amps that this will make for an interesting discussion.

 

I guessed that what you were trying to say is that an electronically generated "sine wave" is never a pure sine wave and always has some amount of harmonics (or distortion if you want to call it that).

In my books,

v = A sin(ωt)

is a pure sine wave with all the energy at a single frequency.

 

Agreed, peace

 

Why do you need a sine wave?

It is something my professor assumed after getting a request (making a frequency doubler) from an external source. Actually the text isn't that specific, so he may be wrong.

I've scheduled a meeting with the guys who want it. Guess I'll find out.

 

View attachment 78716

Is the voltage source to the right really a mixing module? Not sure how you did that.

 

Is the voltage source to the right really a mixing module? Not sure how you did that.

Think of B1 as a multiplier, otherwise known as a "mixer". Note the B1 function sin(x)*sin(x) = sin(x)^2. If you remember your Trig, sin(x)^2 = 1/2 - 1/2 cos(2x).

Perhaps a ready made mixer from MiniCircuits might work for your application.

Poking around on the MiniCircuits web site turned this up:

 

Les - a sinewave has no harmonics, and a sawtooth wave has all integer harmonics. A triangle wave as only odd harmonics like a squarewave, but they fall off in amplitude much faster - as the square of the harmonic number (1/9, 1/25, 1/49, etc.).

ak