Try this for the existing 20/17/15 LPF? ....make the three coils all 350nH with a 47pF in parallel (easy to tack on), the capacitors at the ends are both 220pF, the other two are both 360pF. Like Allison (and everyone else....) says, the spurs move with tuned frequency.....these traps are for ~39MHz and only to vary the LPF roll-off, not to "trap" any 23.xx MHz.
73 Kees K5BCQ
