John F. Crohan, founder and former president of Talk America Radio Networks, died Sunday in Canton, Mass., following a lengthy illness. He was 69. He had previously been diagnosed with a brain tumor.Crohan began his career in broadcasting as a disc jockey in Rhode Island. He later served two consecutive terms as president of the New England Broadcasters’ Assn., and managed WICE in Providence, R.I., and WCOP in Boston. He founded radio stations WPEP in Taunton and WDIS in Norfolk. He also started the New England Radio News Network in the 1970s and later established Talk Radio, a national network broadcast to more than 430 stations and over the Internet. Crohan is survived by his wife, Caroline, three daughters, two brothers and one sister.