Tom says: >That can be as simple as a below chassis/above chassis pressure differential >switch. Tom, is there a source of cheap differential switches that will operate down to, say, 0.1 inch WG? 73 Peter G3RZP -- FAQ on WWW: http://www.contesting.com/FAQ/amps Submissions: amps@contesting.com Administrative requests: amps-REQUEST@contesting.com Problems: owner-amps@contesting.com