I thought you had to have a filter in FL1? I don't know, I bought my K3 factory built and haven't even opened the case. - Keith N1AS - - K3 711 - -----Original Message----- I have filters in FL2 (2.7 KHz), FL3 (1.8 KHz), and FL4 (0.4 KHz). (I'm saving the FL1 slot for an eventual AM 6 kHz filter.)