Distill:FM Barebones - Broadcast FM Bandstop (Notch) Filter for Software Defined Radio (SDR) Applications

If you have an SDR and you live next to an FM radio transmitter than this is your device. It will filter those signals so that you can listen to stuff just outside the FM broadcast band. It works fine.

Installed this on my SDR dongle due to strong FM stations nearby. It works. Completely eliminated FM reception in the 88-108 MHZ FM band. No noticeable loss to other frequencies, although I am sure there is some. The complete FM BCB elimination is not an issue for me, so if your looking for something to "deafen" FM reception, this is it.

I have an older (when it was analog) "flying saucer" RCA TV antenna, which I added a digital TV 45 db "mast amp". In the path towards my city "antenna farm" location, I found 3 cell towers; one of them less than 3 miles. I also have an "amateur FM station", which has a low power setting (+/- 5 watts). And a 15 watts ERP "high power" mode. There's a similar rack version of this same 75 ohm setup, at 5, 10 & 150 watts, using another 5/8 wave Ramsey antenna. This low setting was... is an experiment using Blonder-Tonge ZFMSM CATV FM modulators (yeap, it's 75 ohms). Both, the 75 ohms dipole I built using RG-8 cable & the 5/8 wave Ramsey antennas are 5 meters away from the "saucer" TV antenna. That "saucer" omni has a Radio Shack (RS) 12 db FM filter, but I wanted a bit more; just to overkill. So I took the connectors off. Soldered a pair of "F" female connectors & put the tiny board inside a sealed Altoids metal case. Then placed this Distill "SDR" FM filter between that RS FM filter. In hopes that the Distill's 50 ohm mismatched impedance, gets equalized with the next stage; an Antra ATF-600 4 & 5G LTE MATV cell phone filter (avoiding having to add a 25 ohm resistor load). The MATV mast amp is at 3/4 of gain (33.75 db's) & the FM transmitters audio chain includes a Behringer 15 band dual EQ. A Behringer SX3040 or an Aphex 104 Aural Enhancers... & lastly, the amazing Behringer DEQ-2496 feeding both modulators. Even as the FM mods have audio cut offs below 40 & over 15k, the DEQ-2496 is my last limiter/leveler/expander & audio band pass filter. If I'm listening or watching web radio or video streams, the audio gets an extra "FM DSP" treatment; using an old i7 4 core "lappy". Either with Winamp/Stereo Tool, or an EMU USB audio "dongle" & Stereo Tool Stand Alone version. Oh yeah, by the way. Both the 75 ohm dipole & the 5/8 wave antennas have Ramsey's FMLP1 FM band pass filters. Plus a single specific FM channel band pass I built, for the empty FM channel in my area which I'm "borrowing" (can't afford cavity filters). The audio is as good & even better than some public & commercial FM stations & as you can see, I take RF & audio filtering very, very seriously. I have an old not lately calibrated RF spectrum analyzer, but borrowed an FM Deviation analyzer & other FM measurement tools from... an engineer at a local radio station. Did tests & guess what ?. My "amateur FM station" does not overmodulates; drifts & pretty much "signal legal", even as legally... . Heck, my side bands won't interfere with any adjacent or far off FM channels... measuring or listening right next to my FM antennas. RF filtering is a delicate proposition & I'm so glad this Distill FM filter worked as good as I envisioned it will. My SDR "musings"... also use this filter with excellent results.

Edit: This is accurate per the description of >40dB at peak -48.24dB attenuation at 91.4Mhz. Revised review as the description is accurate. See picture of VNA for filter shape. It does it's job and I assume in some places it gets close to 40dB, so it's a fairly accurate description. $10, it's not bad, but there is better out there. The official RTLSDR blog one is much better.

Good specs

I live about 4 miles from a 100kW FM station, and it really messes with my software defined radio front ends. Putting this in front made a noticeable difference. I've read some other reviews that say it doesn't attenuate enough, but for the price it did just fine in my situation to make my SDRs more usable.

Needed to block the very strong FM radio stations in my area. I brought two one from my NOAA system and one spare. connected to the SDR and fired up SDR# and went to the FM broadcast band and was able to pickup all the local stations. (See Screen shot of SDR#) It didn't block any of the FM stations at all. I Even can see the carrier of 107.9 WSRZ out of Sarasota FL is over 30miles to the south of my location. so it doesn't even block what is normally a weak signal at my location.. I also tried it before and after my LNA and saw no change. AND On top of all that one of the Notch Filters came with the RF shield crushed.. See Pictures

Works well, tried it out with an rtlsdrblog v3 for listening to cb, this filtered out the broadcast fm images that usually appeared there

Salve ho letto tante recensioni su questo filtro molte positive altre un po meno. Quindi ho deciso di fare una prova strumentale con analizzatore di spettro con TG. La curva non è lineare attenua poco agli estremi ma a 94 mhz oltre 50 db . Considerando il costo d' acquisto non male. Chiaramente ci sono filtri che hanno altre caratteristche ma hanno costi molto elevati

Remplis très très bien son objectif, indispensable avec un ampli .

work very well it block a lot of undesirable signals in a noisy place like in big city i love it!

very good product

This filter are for people who wants to preserve full signal at 118MHz and above and at 82MHz and below. It attenuates 20dB at 90Mhz and 103MHz. A 94MHz it has it deepest null at 40dB. It still has 30dB at 92MHz and 101MHz. There are other filters for people who needs much more attenuation at the FM broadcast band edges and doesn't care so much for VHF air band and the upper end of VHF-LOW. For most people if will do its job and are an excellent filter at this low cost. My scanner with CloseCall immediately detected a 390MHz transmitter in a tower 3km away and a mobile guy transmitting at 69Mhz 1km away when the filter was installed.