both of the filters I am using the braid breaker type of high pass filter. I have one right on the input to the freeview box and another in the attic to the input of the tv distribution amp. Every lead out to other tvs has ferrite blocks. The mains in also has ferrite choke and the gain is wound back so not to overload the tvs. I run the Vhf fm radio feed via a separate amp so no interaction there. The tv antenna is an (expensive) high gain (no preamp) on a mast outside the house away from transmitting antennas and i had the cable renewed too at the time of fitting. The mains supply to the freeview box if of the rfi filter type as is the feed to all tx gear.
Ask Humax for tech advice !!!! They could not even tell me what the dial on the front does or why it is not mentioned in the user guide!!
Duplexer notch sounds a good idea. i need a local rally.
73 ken G4apb