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

[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??

 

[Simon Bridge]

Where have you seen a negative frequency occur?
Something like http://forum.allaboutcircuits.com/archive/index.php/t-60531.html?

 

[klmnopq]

yes.

 

[Simon Bridge]

The link explains them.

 

[okami11408]

Negative frequency is nothing but phase reversal.

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

 

[marcusl]

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

That's not even close to correct.

 

[okami11408]

Im sorry its sine not cosine.

 

[marcusl]

Negative frequency is nothing but phase reversal.

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

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
$$V(t)=\Re\{\cos(\omega t)-j\sin(\omega t)]\exp(j\omega_0 t)\}$$