Hello Pawel,
I changed my HB-QDX to 30-20-17-15-12-10m. I took the LP filter 20/30m from the LB-QDX, wound the RX filter for 30-20-17/15-12/10.
You have to make a compromise, the transmission curve is not wide enough on all bands.
I wound and tuned the RX coil band by band, a calculation didn't work well for me, and only installed it properly at the end
73 Reiner
dl8lrz Reiner