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.

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.

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.

When I bought this the listing claimed a much higher attenuation (like 24 db) this device doesn't even come close to that. In fact it says 6db right on the circuit board (fine print on the back of the circuit board)Note that this is a "band stop" filter or "notch" filter.My apologies for blurry close up phone pictures, but I have one and it says:"<-3db 82MHz - 115MHz" (this description lacks important details like FWHM? or what measurement was actually taken)"<-6db 87.5MHz - 108MHz" (see note above)What this means is that it will reduce the power of a US or Euro FM radio station about the same amount as doubling your distance from the actual radio source (a factor of 4) this is not very much attenuation if you are 2 miles from a powerful FM station so you may want to keep shopping.I"m satisfied with mine, it deloads the front end of my SDR radio. Do note when you are using this it needs to be in an RF cage of some sort, out in the air (on your desk) it will be noisy.

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.ANDOn top of all that one of the Notch Filters came with the RF shield crushed.. See Pictures

Worked great. Local FM stations where over driving the front end on my RedPitaya SDR.

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.

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

Buen producto. Todo muy bien.

Substantialy reduced mirror signals from strong broadcast fm when using sdr on hf bands

Très bon filtre anti fmM’a totalement supprimé l’es onde fm sur mon sdrJe recommande.Ps: aucun besoin de l’alimente

rispetta la curva di attenuazione 20 db