[Discuss-gnuradio] hardware impairments: phase noise generator documentation ?

I am trying to model 1/f phase noise.  There is a phase noise generator

block in gnuradio.  I have been unsuccessful in locating documentation

of this hierarchical block that describes what the two parameters mean.

There is just one line in the hardware impairments section listing that

it exists and take two parameters.

The GRC block shows the two parameters:

* Noise Magnitude (the level of the phase noise in db)

   Magnitude at what frequency?  One Hertz?   Something else?

* alpha:  can't find anything at all describing what this is.

Does this block generate 1/f noise in order to phase noise impair the signal?

Is there any documentation available?

Thanks for any help folks may be able to provide.

-- Tom, N5EG