In this letter, a large scale investigation is carried out, utilizing several spectral shapes as the source for direct modulation based frequency dithering (DMFD). DMFD mitigates the nonlinear effect of long term evolution (LTE) radio-over-fiber (RoF) systems. The dithering signal shapes are; sine, square, saw, sinc and Gaussian with different spectral width characteristics. We show that by varying the dithering signal with increasing spectral width, no additional distortion is introduced in the linear and optimum optical launch power regions, which are dominated by the frequency chirp and chromatic dispersion (CD). Additionally, it is revealed herein that introducing dithering signals with varying spectral widths does not change the nonlinear compensator characteristic towards suppression of nonlinearity. The reason for this is that as long as the optical source linewidth is larger than stimulated Brillouin scattering (SBS) linewidth, the proposed method completely suppresses SBS. Finally, the degree of freedom for the dithering signal is infinite, with an optical power budget improvement of up to 8 dB at an optical launch power of 10 dBm, which can in turn be used towards connecting multiple relay nodes (RNs).