# Sine wave frequency 2

Discussion in 'Electronic Design' started by thejim, Dec 13, 2005.

1. ### thejimGuest

I wasn't very clear in my first post regarding sine wave frequency.
What i am trying to say is if can we have a sine wave of frequency 40
or 50 or 60 Hz.
Suppose we have a sine wave frequency. By decreasing or increasing
the frequency from a limit and on the wave stops from being sine or is
not?

Thank you

2. ### Paul BurkeGuest

It's not dreadfully clear what you are asking; though if I asked a
question in wg=hatever is your native language (Greek?) I doubt if it
would make any sense at all.

This is an answer to what I think is your question.

A sine wave is defined as a voltage/ frequency/ whatever which varies as
a function of time such that the instantaneous value V = Vm sin wt. Vm
is the peak absolute value, w is 2*pi*frequency, and t is time.

Obviously, any deviation from that relationship makes it, strictly
speaking, not a sinewave. The deviation could be noise, distortion,
maximum amplitude variation, frequency variation etc. A Fourier analyser
attached to the signal would show these up as the base level, harmonics
etc. as well as the pure single fundamental of a sinewave.

You are talking of a signal which can be expressed as V = Vm sin w(t) t,
where w(t) is itself a function of time- in your case, I think, a ramp.
You can plug that function into the Fourier calculation, do the sums and
come up with the answer, for any function of time that you choose.

But we are a bit lax, and basically if it LOOKS like a sinusoidy
squiggle on the scope, we call it a sine wave. Most of the time,
everybody understands, or don't care anyway.

Now, why do you need to know?

Paul Burke

3. ### PeteSGuest

I think what you are asking is:

Start with some sine wave at arbitrary v = ASinw(1)t and vary the
frequency to some new signal v = ASinw(2)t.

Is that correct?

You are then asking, if one does this, will the result still be a sine
wave?

Is that also correct?

At all instantaneous points (time) during the transition, you will have
a single sine wave, assuming you are simply changing the frequency of a
single source.

Cheers

PeteS

4. ### theJackalGuest

I am guessing what you are trying to say. Possibly you want to vary
the frequency of a Sine wave oscillator you have designed or have.
Your question is by simply changing a component value or 2 do I still
have a Sine Wave? If you are using an Analog oscillator I'd think
No. Don't believe what the books say it won't work so easily . You
have to redesign the whole thing.
With a digital oscillator ... Yes very likely.

If your question is about Sine wave purity ... Yes it can be
compromised by changing the frequency. It all depends on the details
on what you are using to generate the thing.

"Go easy on the whisky"

theJackal

5. ### Peter BennettGuest

A sine wave may be any frequency you wish - from one cycle per week or
more, up to Gigahertz.

6. ### Charles SchulerGuest

I think you might be asking about frequency modulation. If you are, the
result is a group of sine and cosine functions (frequencies) that can be
predicted with Bessel functions.

7. ### Phil AllisonGuest

"theJackal"

"theJackass"

** This laughing Jackass piece of *Eurotrash* is a pure vermin.

Must be posting straight from an asylum for the criminally insane.

....... Phil

8. ### Rich GriseGuest

I understood well, I've just been reading your thread waiting for someone
else to get it.

A sine wave can be at any frequency, and still be a sine wave. The term
"sine wave" just defines the _shape_ of the wave, but the wave can be
at any frequency you wish. (well, within limits, of course).

If you put a small pen sticking out the bottom of a pendulum bob, and
drag a piece of paper under it at a constant speed, it will draw a
sine wave.

And someone else has already typed the trig expression, which boils
down to y = sin x.

Hope This Helps!
Rich

9. ### theJackalGuest

LMAO Phil you are too repetitious.

But better die than live mechanically a life that is a repetition of
repetitions.
D. H. Lawrence

"Go easy on the whisky"

theJackal

10. ### Phil AllisonGuest

"theJackal"
"theJackass"

** This laughing Jackass & psychopath is pure usenet vermin.

Likely posting direct from an asylum for the criminally insane.

His comments are all plagiarised from Google.

Would almost be funny - if he was not so dangerous.

......... Phil