Wave Trap

I have an old tube regenerative radio, but where I live, there's a
powerful radio station that overpowers the other weaker stations, I
want to build I wave trap, already have a 2 gang variable capacitor
sitting around, unknown value, that maybe I could use. Is there any
way I can measure this using the capacitance feature on my
multimeter? What size coil wire would I need?

Thanks, Dave
.