Why would the winding of toroids be a problem only for QRP Labs filter kits and not for *any* project that has toroids to wind?Bill,
Yes, The QRP Labs LPFs and BPF use standard designs.
It seems to me that very often that when I have wound toroid coils for any project the inductance is a little high. Possibly due to the ferrites being at the high end of their spec.
A tested-accurate inductance meter may help otherwise it is trial and error as detailed in the assembly instructions.
73 Alan G4ZFQ