Typical usage pattern
You can set tuning frequency either typing it in Frequency MHz box or Ctrl+Click at some point of the signal on the Chart (Line or Waterfall). Parameters depend of characteristics of the signal you want to listen to. You can choose FLAC or OGG codec but as far as I've tested FLAC is highly recommended for the Raspberry Pi B+ because of OGG high CPU usage. Pressing button "Start" sends the command to the RPi and as soon as command is executed "Stream URL" turns green and stream address shows up in it. This doesn't mean demodulation or transcoding or streaming was occurring but only the command is successfully executed on the RPi. You must select all parameters correctly in order to get audio stream. Now you can type or copy/paste stream url at your favorite stream player and listen to the audio. But I would recommend some with FLAC support, because of reason I've already mentioned.
SSH Tunnel (Experimental) check box, when checked It is going to redirect audio stream to Your local Computer by SSH connection. That way you can listen to the stream on the PC (where MNM4SDR is running) even the RPi is behind firewall, NAT translation for the SSH connection is still necessary but not for the audio stream. Here are some examples.

Professional Mobile Radio (PMR)
Channels wide is 12.5kHz and modulation is FM. It is obvious what to select as "Modulation". Rounding to first whole number gives 13kHz for "Bandwidth kHz". This 13kHz gives us conclusion about "Stream BW bit/s". Since it must be lower the only possible value is 8000 (8kbps), this is because option -r (resampling) of rtl_fm is used and set to value of stream rate (stream BW) so it doesn't make sense to resample with higher rate than the sample rate (Bandwidth kHz) is. You can also control Squelch but be careful because if transcoder doesn't get something on the input, there is nothing to be streamed.



FM broadcast stations
Channel is 200kHz wide and modulation is FM. Accordingly to help of rtl_fm option -M wbfm is equivalent to options -M fm -s 170k -o 4 -A fast -r 32k -l 0 -E deemp but not sure if explicitly stated options override it. That's why we are going to set parameters as follow:
  • Modulation: wbfm or fm, It doesn't metter.
  • Bandwidth: 200kHz, but I'll set it wider, 250kHz
  • Stream BW bit/s: less or equal to 200kbps. So we can choose any value from the list based on available network bandwidth.


Last edited Aug 8, 2015 at 4:18 PM by skrilic, version 22