He's getting RFI at one frequency. I was thinking an open quarterwave
coaxial stub tuned to 100.5 MHz would serve to trap the offending signal,
and be easy to implement. Cut it a tad long from the calculated length,
connect it to the analyzer input using a tee adapter, and "tune" it up in
frequency using a pair of wire cutters:

246/100.5 = 2.45' (or 2' 5-3/8") * Vf

Bryan WA7PRC

What will that stub look like above and below the notch frequency? It sure
won't be invisble.
eg: 50 Ohm cable is around 27pF/'.
Dale W4OP