I know that this receiver from 0,03 to 30 MHz has 11 RF filters (3 low-pass and 8 bandpass). When I tuning from 0,03 to 30 MHz, ONLY at 15 MHz the double click of the change of filter is audible and for an instant the green led on the front panel is off. Is it normal or this means that the other filters are not activated? Thanks to everybody. Aldo Briga