There is an article on such a filter in the February, 1986 QST, p15ff written by N4UU. It splits the audio and processes it in two channels. There is a CW version and an SSB version. Good luck, 73 and 161 Don K5AQ -- FAQ on WWW: http://www.contesting.com/FAQ/topband Submissions: topband@contesting.com Administrative requests: topband-REQUEST@contesting.com Problems: owner-topband@contesting.com