band filter

I made a bandfilter for 7 MHz. It should filter the input/output to/from the 7 MHz port of the mixer.

It consists of 3 tuned circuits. The coils are made by 18 turns on a T50-2 core. Coupling between then is done by a 1 turn link coupling.

It works but I am not satisfied. It is probably good enough but it can be made sharper. I think the link coupling is too tight. The link coupling is a piece of wire (ring) between two cores. This coupling is good, probably too good.
I will change the coupling by a capacitor coupling.