I bought a cheap FM bandstop filter and measured it using a unreasonably expensive R&S Spectrum Analyzer. The bandstop seems pretty good for the price. : r/RTLSDR
88-108 MHz bandstop filter for FM rejection
Broadcast Fm Band Stop Filter (88 - 108 Mhz Fm Trap) By Rtl-sdr Blog | eBay
PISWORDS - FM BandStop Block Filter For 88 - 108 MHz
1-3000mhz Fm Band Stop Filter 88-108Mhz For Rtl-sdr Blog Shortwave Ham Radio - Walmart.com
FM-Band LC Band Pass Filter - AWG RF
1-3000mhz Fm Band Stop Filter 88-108Mhz For Rtl-sdr Blog Shortwave Ham Radio | eBay
Amazon.com: 88-108M Band Stop Filter Stop Band 76-120MHZ Passive Notch Filter Anti-Fm Interference Filter Low Insertion Loss : Industrial & Scientific
88-108 MHz band stop filter radio accessory communication system FM transmission - Walmart.com