Mark, I posted this question a few days ago and I received a very helpful response that came through private email. There are two programs available DX2ADIF and ADIF2CBR that will do this for you. The first will take the DX4WIN ADIF and output a new ADIF with the frequency field included. It cleverly extracts it from the notes field. The second will create the Cabrillo file from the new ADIF. Here is the web site, click on Converters:
http://sp7ps.pl/sp7dqr/eng/index_en.html Hope this helps. 73, David - N5USH

