You most likely can't "fight" it: while you can request as "discovery" (information & documentation the other side must share with you) information about the calibration and testing of the radar gun and the cop's training in using it, in my experience, that information will come back showing that the gun worked right and the officer was properly trained. If that  occurs--and again, it's my experience that that's what will likely occur, since the police departments know how to use and maintain radar--then the judge will believe the sworn, allegedly impartial police office that he clocked you correctly. Only if, against expectations, such discovery shows a problem with the gun's maintenance or the officer's training with it are you likely to have any chance of convincing the judge he's wrong.You are much more likely to be able to negotiate a more favorable plea--no or fewer points, and/or a lesser fine. Speak to the prosecutor before court (show up early); be respectful and contrite; stay you thought you were at or maybe just a few (e.g. 2 - 4) miles over the limit at most, but don't get belligerant or argue the point--just state it. If you otherwise have a clean record, most prosecutors will offer you a favorable deal.