Load an old saved game file. Shoot in Highpool or Agricultural Center until someone reports you to Vargas. Travel north to the Rail Nomad Camp, and continue killing until someone reports you to Vargas again. After the first report, you can lie to Vargas about why you had to kill the people. After the second report, Vargas will get very angry and send Team Delta after you. This will be a random encounter on the world map. At this point the game may not be complete-able, which is why you want to use an unwanted saved game file. You will not be able to use the radio because you are no longer a Ranger.