about 17 inches by 24 inches 43 18 cm by 60 96 cm for comparison purposes a typical ku band transponder usually operates at a data rate of approximately 30 mbps using conventional vsat antennas using a standard digital video broadcast dvb waveform the forward link signal typically occupies less than 8 mhz out of a total transponder width of 27 mhz however concentrating the transponder power in less than the full transponder bandwidth could create a regulatory concern fcc regulations presently regulate the maximum effective isotropic radiated power eirp spectral density from a transponder to prevent interference between closely spaced satellites accordingly in one preferred embodiment of the system 10 spread spectrum modulation techniques are employed in modulator 70 to u201c spread u201d the forward link signal over the transponder bandwidth using well known signal spreading techniques this reduces the spectral density of the transponded signal thus eliminating the possibility of interference between two or more mobile terminals 20 it is also equally important that the transmit antenna 74 meets regulatory requirements that prevent interference to satellites adjacent to the target satellite 18 the transmit antennas used in most mobile applications also tend to be smaller than conventional vsat antennas typically reflector antennas that are 1 meter in diameter mobile transmit antennas used for aeronautical applications should have low aerodynamic drag be lightweight have low power consumption and be of relatively small size for all these reasons the antenna aperture of the transmit antenna 74 is preferably smaller than a conventional vsat antenna vsat antennas are sized to create an antenna beam that is narrow enough to illuminate a single fss satellite along the geosynchronous arc this is important because fss satellites are.