# Harmonic carriers

Discussion in 'Electronic Design' started by Martin Harris, Jun 23, 2007.

1. ### Martin HarrisGuest

I am trying to understand how an harmonic carrier is properly applied
and what the effect is.

For example, if I tale a 1KHz sinewave and use it to AM a 16KHz
sinewave do I get harmonics higher than the 16KHz?

Any expert insight?

Martin Harris

2. ### Hal MurrayGuest

I'm far from an expert, but that's pretty basic.

You will get energy at 16-1 and 16+1 KHz. No harmonics of the carrier.

You will get harmonics/splatter if you overmodulate.

http://en.wikipedia.org/wiki/Amplitude_modulation

3. ### Simon S AysdieGuest

Ideally, no. But, no system is perfectly linear. There will be some
level of harmonic response. How much is acceptable and why are the
questions.

4. ### Rich GriseGuest

Not harmonics - sidebands. If your 16KHz is a pure sine wave, and your
1 KHz is a pure sine wave, and your modulator is "linear" (modulation
is a non-linear function - what I mean here is that the amplitude of the
carrier exactly follows the input), then the output will consist of
a signal at 15KHz, 16KHz, and 17KHz - the two sidebands will be half
the amplitude of the carrier (16KHz)

Hope This Helps!
Rich

5. ### ChuckGuest

As has been said by the other posters,
modulate linearly, the entire output
spectrum will consist of just three pure
sine waves.

Perfect amplitude modulation wouldn't
generate harmonics of the carrier.
However, AM is often applied to a
high-level stage or power amplifer that
is operating in some mode other than
class A with less then perfect high-pass
filtering. Consequently, that stage will
generate harmonics of the carrier
frequency. And if the carrier is being
modulated, so will the harmonics. But it
is not the modulation process that
generates the harmonics of the carrier.

maybe you can supply some additional
details.

Chuck

6. ### Martin HarrisGuest

Due to the nature of my inquiry, it was assumed I wanted to minimize
harmonics. Understandable by convention. But actually, I would like to
_maximize_ them, especially on the higher side. IOW to obtain as many
higher above audio harmonics of the 16KHz as possible while still
using something like the sinewave AM approach originally described,
ie. not squarewaves. What would be the best way of achieiving this?

Martin Harris

7. ### Phil AllisonGuest

"Martin Harris"

** Physics is not game where YOU get to make up any rules you like -
fuckwit.

Harmonics are generated by distorted looking wave shapes - NOT sine waves.

A square wave has all the odd numbered harmonics included - 3rd, 5th 7 th
etc. .

Asymmetrically distorted sine waves have the even ones, 2nd 4th, 6th etc.

A mix of the two gives you the lot.

An electric guitar fuzz box does this to a sine wave input.

....... Phil

8. ### Robert BaerGuest

Not quite correct; one gets the sum (16+1), the difference (16-1),and
the originals (1 and 16) KHz.

9. ### Robert BaerGuest

Why is it that "everyone" is ignoring *both* of the original input
frequencies?
Perhaps one needs to use a spectrum analyzer...

10. ### Robert BaerGuest

Use a filter tuned to 17KHz.

11. ### ChuckGuest

Kind of depends on the circuit, doesn't
it, Robert? What if a DBM were used?

If the intent is to produce modulated
harmonics of a sine wave carrier, I
think the answer has been given: you
must modify (i.e., distort) the sine
wave carrier in order to produce
harmonics. For example, use a circuit
that distorts the sine wave by clipping
it. The modulator could perform this
function.

A pure sine wave simply contains no
energy other than at its own frequency.
If you're not willing to distort a sine
wave, you can't produce harmonics. Period.

parameters of your enterprise, it is
really difficult to respond further.

Chuck

12. ### Rich GriseGuest

Just generate a 16 KHz sawtooth; you'll get harmonics:
http://en.wikipedia.org/wiki/Sawtooth_wave

Or, if you want there to be harmonics of 1 KHz all around the 16 KHz
carrier, them AM it with a 1 KHz sawtooth.

Have Fun!
Rich