The radio industry last year turned in its best performance since 1985, according to figures released Tuesday by the Radio Advertising Bureau.Radio advertising revenue last year grew 9.3% to $ 9.5 billion from $ 8.7 billion in 1992, the bureau reported. Locally placed advertising, which accounts for roughlythree-quarters of all radio ad revenue, jumped 9.2% in ’93, while national spot grew 10.2% and network rose 8.1% for the year, according to the RAB. RAB president Gary Fries said that early indicators signal a strong 1994, with revenue growth on par with that of last year. National spot revenue, which experienced a 6% decline in 1992, posted double-digit growth in ’93. The biggest increase came in December, when revenues were up 20%.