🚀 go-pugleaf

  A fair technique would be to use a tuned stub - a piece of coax cut so as
to be (I believe) 1/4 wavelength at the frequency you want to notch.

  At 100 MHz, this would be on the order of a few feet of coax; doesen't
seem like a problem.

  It's how we routinely notch out signals from a tower radiating several
megawatts only a mile away (megawatts because at least six stations use
the tower).

  The nice thing about it, is that since you make it yourself, you can tweak
it by trimming it shorter until attenuation is max.  Careful, though-can't
make it longer if you cut too much.

  The response is periodic, but since you're looking at a narrow band I don't
expect you'll see any but the fundamental response.