December 7, 2015

Low Pass Filter

If you want to save some money on a custom FM Notch filter but spend a little more vs a $5.00 Radio Shack FM Trap then I strongly suggest you check E-Bay for a 2nd hand Mini Circuits BLP-21.4+. They go for about $20.00 used and will notch out everything from 27 Mhz threw 200 Mhz.These are very useful to notch out local and strong FM broadcast bands, NOAA, Hospital Pagers and anything like falls within 27-200. Data sheet is here. I will post some before and after pictures showing how well this inline filter really works


  1. I live near Wash DC and want to try one of these. My SDR MW waterfall has bars every 10 kHz but many of these have no audio. Question I'm mainly interested in MX DX and pirate radio. Is it worth upgrading my Afedri to an Elad-FDM-S2 or is my high noise floor the limiting factor?

  2. Bars every 10Khz is a sign of RFI/Noise from within the shack. Most noise is from switching power supplies. I would sweep the whole shack and disconnect each one from the socket while looking at the waterfall. The Afedri is a very capable SDR and is most likely not the issue.