  In the context of Radioastronomic applications where the Analog
Radio-over-Fiber technology is used for the antenna downlink, detrimental
nonlinearity effects arise because of the interference between the forward
signal generated by the laser and the Rayleigh backscattered one which is
re-forwarded by the laser itself toward the photodetector.
  The adoption of the so called dithering technique, which involves the direct
modulation of the laser with a sinusoidal tone and takes advantage of the laser
chirping phenomenon, has been proved to reduce such Rayleigh Back Scattering -
induced nonlinearities. The frequency and the amplitude of the dithering tone
should both be as low as possible, in order to avoid undesired collateral
effects on the received spectrum as well as keep at low levels the global
energy consumption.
  Through a comprehensive analysis of dithered Radio over Fiber systems, it is
demonstrated that a progressive reduction of the dithering tone frequency
affects in a peculiar fashion both the chirping characteristics of the field
emitted by the laser and the spectrum pattern of the received signal at the
fiber end.
  Accounting for the concurrent effects caused by such phenomena, optimal
operating conditions are identified for the implementation of the dithering
tone technique in radioastronomic systems.
