# What's negative frequency in analysis of s domain and w domain

1. Feb 13, 2013

### klmnopq

what's negative frequency???

can we say s=-3 in example bode plot !!!!!
or we can say it's unstable at w=-3 rad/s

that's I mean is there negative frequency????????????

2. Feb 13, 2013

### Simon Bridge

Re: what's negaive frequency in analysis of s domain and w domain

Where have you seen a negative frequency occur?
Something like this?

3. Feb 13, 2013

### klmnopq

Re: what's negaive frequency in analysis of s domain and w domain

yes.

4. Feb 14, 2013

### Simon Bridge

Re: what's negaive frequency in analysis of s domain and w domain

5. Feb 14, 2013

### okami11408

Re: what's negaive frequency in analysis of s domain and w domain

Negative frequency is nothing but phase reversal.

eg. sin(2pi(-f)t)=-sin(2pi(f)t)

Last edited: Feb 14, 2013
6. Feb 14, 2013

### marcusl

Re: what's negaive frequency in analysis of s domain and w domain

That's not even close to correct.

7. Feb 14, 2013

### okami11408

Re: what's negaive frequency in analysis of s domain and w domain

Im sorry its sine not cosine.

8. Feb 15, 2013

### marcusl

Re: what's negaive frequency in analysis of s domain and w domain

The concept of negative frequencies makes sense for complex or quadrature data, that is, when you consider both sine and cosine components impressed on a carrier according to
$$V(t)=\Re\{[\cos(\omega t)+j\sin(\omega t)]\exp(j\omega_0 t)\}$$versus
$$V(t)=\Re\{\cos(\omega t)-j\sin(\omega t)]\exp(j\omega_0 t)\}$$