  For the first time the linewidth of Flux-Flow Oscillator has been calculated
by direct computer simulation of the sine-Gordon equation with noise. Nearly
perfect agreement of the numerical results with the formula derived in [Phys.
Rev. B, {\bf 65}, 054504 (2002)] has been achieved. It has been demonstrated
that for homogeneous bias current distribution the linewidth actually does not
depend on the junction length for practically interesting parameters range.
Depending on the length of the unbiased tail, the power may be maximized and
the linewidth may be minimized in a broad range of bias currents. The linewidth
can be decreased further by 1.5 times by proper load matching.
