The Federal Communications Commission sent four warning letters about unlicensed use of radio transmission equipment to northern New Jersey microcasters in the past four weeks. Someone, apparently, called in two Jersey pirates on Nov. 4, and another on Nov. 8. On Nov. 29 the FCC sent a "Notice of Unlicensed Operation" to "Jain and Jain, Inc." operating on 102.3-FM from 214 Glenwood St. in East Orange. That same day they sent a nearly identical letter (except it says they learned about his operation on Nov. 8) to Perkin A. Diaz, who they contend was operating a station at 90.5-FM from 439 E. 32nd St. in Paterson. Then on Dec. 7, the FCC notified Manuel Carbajal (99.9-FM at 256 Clifton Ave., 2nd fl, in Newark) and Wayne Phillip (also on 102.3-FM at the same address in East Orange of "Jain and Jain, Inc."). So three stations in four weeks have been reported, observed, and sent letters from the FCC's New York City office.