There is no reason you are limited by your undergraduate degree. Degree in English is perfectly fine to pursue graduate school. Furthermore, your professional background working in radio broadcasting sure helps your resume in the admission/application.
As for choice of school, it is probably the best to look under School of Journalism. Some websites, such as usnews.com, give you a list of top schools in the field of journalism. I would suggest you to look in their websites and see if broadcasting is one of their strength. For example: Medill (Northwestern University) offers concentration in Videography and Broadcasting.
Wikipedia lists more details info on J-school: http://en.wikipedia.org/wiki/Journalism_school, you can find a list of top schools in the article. “Schools such as New York University, University of Texas, Ohio University, Indiana University, Columbia University, University of Maryland, University of Kansas, University of Missouri, Michigan State University, Northwestern University, Syracuse University, University of Minnesota, University of Florida, University of North Carolina, Chapel Hill, University of California, Berkeley, and University of Wisconsin-Madison are typically considered among the best in the United States based upon the success of those who attended these institutions.”
Comment: watch out, J-school is expensive and competitive.