Can we generate signals in reality that have non symmetric magnitude spectrum in the Fourier domain? I am reading communication systems, and have a doubt:
Is it possible to generate signals in reality that have a non-symmetric magnitude spectrum in the Fourier domain?
For example, if I have a signal
$$u(f)$$ or something like this as Fourier domain representation 
I know that their Inverse Fourier transform is going to have imaginary element $j$ in them, but does this $j$ just symbolize 90-degree phaseshift, can I generate signals in reality that have asymmetric magnitudes of their Fourier transforms.
I have read that $j/-j$ just represent a 90-degree lag or lead, but do such signals with asymmetric magnitude spectrum in the Fourier domain exist in reality?
This will also clear my doubt that whether there are such signals in reality that have just positive/negative frequency components in their Fourier domain representation.
As the answers suggest having $j$ just means phase shift, but if some practically permissible signal has representation $jm(t)$, where $m(t)$ is real, with no imaginary component, then with respect to what I have to define the phase.
Or such a condition will never arise where the inverse Fourier transform of a signal is purely an imaginary quantity.
As @Bob said, it depends of your definition of &quot;in reality&quot;. I am going to ignore images on this post and focus on signals as a function of time.

One-dimensional signals always have a symmetrical magnitude spectrum. Examples are the voltage or current on a wire, or a sequence of real numbers stored in digital memory.

Two-dimensional signals may have a non-symmetrical magnitude spectrum. Examples are complex signals, whether defined mathematically or stored in a digital memory; and the voltage or current on two wires, one of which is labeled $\sqrt{-1}$ and with the agreement of doing complex arithmetic (see $9\rm V$ Battery with $45^\circ$ phase).


In my opinon, all these signals exist in reality, and then the answer is that yes, some signals in reality may indeed have a non-symmetrical magnitude spectrum.