So I’m still mad about the FM Spectrum (88-108MHz) noise I get when using a LNA or something else. So I’m still looking for a nice and easy way to filter out these signals.
Last time I posted about a TV/FM Diplexer, that works great, but doesn’t attenuate enough the signals. So the solution would be cascading several of them, but I found that is very hard to find one Diplexer or FM Trap filter those days.
So I started looking out how to make my own filters. So I reopened Adam’s Website (LNA4ALL) that have a small filter he did for FM Trap and tried (again) to make my own.
So it has been a time since my last post (again). Today I’m writting about a TV/FM Diplexer that I bought to address a issue that I’m having here with my NOAA stuff.
So the biggest problem is that in São Paulo the FM Radio (88-110MHz) are VERY strong. I can receive a -40dBm signal with a RTL-SDR with no gains in almost all channels. This is a big issue since the RTL-SDR does not have a input filter (actually it has, see my patches at https://github.com/librtlsdr/librtlsdr ) the LNA gets very easily saturated when getting gains over 25dB (usually needed by APT Signals). So I start to search for a FM Band Stop Filter. But it turned that it was not so simple to do a good FM Band Stop Filter.
So I started searching for a commercial filter, and I noticed that most of the FM Filters were discontinued a few years ago and the only thing I could find was a FM/TV Diplexer.