Hi John, Here is an article which should address your question. It is applicable to any receiver fitted with a front-end attenuator and RF gain control. http://www.ab4oj.com/icom/dbmheaven.html See also: http://www.ab4oj.com/icom/nf.html Cheers for now, 73, Adam VA7OJ/AB4OJ Scanned for viruses by Blue Coat http://www.WinProxy.com/