If you do the MARS modification the FT-817ND will transmit on the CB frequencies...BUT, the performance will be less than that of a made for CB radio. The little radio is 'finicky', it doesn't like to transmit outside of its factory specifications at full power. It will do the MARS freq. ok, but they are not as far outside the regular amateur freq. as the CB freq. Don't let some 'Golder Screwdriver' try to 'tweek' the power output the this radio. The 817 is far more complicated than the typical CB and the radio WAS NOT designed to run more than its 5 watts. Because of the expense of the radio and other problems that I have (and have not) mentioned, I would get a regular CB radio, it will be cheaper and more reliable. Are you not proud of me? I did not say anything about the legality of using the radio on CB freq. OOPS, I did didn't I...o'well sorry. Good luck.