🚀 go-pugleaf

I need a VERY sharp notch filter (or actually 3, if sharp enough) to reject
FM broadcast stations from an antenna signal. The requirements are tough:
a. VERY sharp - I need to measure spectra of broadband noiselike signals and
the present LC filters make a far too visible hole.
b. No other holes (or even ripples) in the pass band - 57 to 180MHz.
c. Low loss.

LC type circuits are not sharp enough. Using a crystal is out as it is too
lossy and has many other smaller holes. A carefully made cavity may be the
answer, but while I can find many ways to use a cavity to reject one
frequency and pass another (standard diplexers), I can't see how to use one
to only reject a frequency, while passing all others. Any help?