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i'm trying to get rtl_sdr to record it's output to wav. i can in a round about way do this, because rtl_sdr allows saving the raw i/q stream to file, which i can then use sox to convert it to a wav file, but the raw data files are very large. the main goal of this is to have my pi record the audio of passing noaa weather satellites for image decoding, but so far i havent been able to do this. everthing i record is static. so, i dont know if i am converting the raw data to wav wrong or if it's something else. this is what i am doing right now:

capture the raw data:

rtl_sdr -f 137.620e6 -s 2048000 -g 29 -p 22 NOAA15.bin

and then convert to wav:

sox -t raw -b 16 -e signed-integer -r 11025 -B -c1 NOAA15.bin NOAA15.wav

then use the apt decoder to get the image:

atpdec -i rabct NOAA15.wav

but all i get is static. this may all be wrong, but i've also tried using rtl_fm to just record a local radio station, but all i get is static there also. i've played with different gain levels, tried auto gain, different sample rates, etc. if i use rtl_tcp to host the stream, i can hear the radio and decode images, using sdr# on another pc. but, after a while, the stream freezes or something, like this video (around the 1:33 mark) http://www.youtube.com/watch?v=8snz1wQSRpw

plus this requires another computer, and i would like to get it all done on the pi if possible. anyone tried to do this before, or have any suggestions? i'm open to ANY!

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  • The tiny supplied magnet mount antenna is not good. But a 2m circular open loop of solid wire, thick enough to maintain shape, with one end attached to the coax center, and the other to the shield, is OK for FM listening, 144Mhz-148 Mhz ham radio, and USA weather forecasts around 162.55 Mhz. Embed the loop in the vertical plane for instance by hanging it on the wall on a nail. It receives the most signal in the two directions perpendicular to the plane of the loop.
    – Paul
    Commented Sep 24, 2014 at 11:26

2 Answers 2

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You are recording raw data (I/Q-samples) and not the demodulated Audio. Atpdec needs the demodulated audio of the satellite. I would try

rtl_fm -f 137620000 -s 11025 -g 29 -p 22 - | sox -t raw -e signed -c 1 -b 16 -r 11025 - recording.wav

and then atpdec recording.wav

Regards, Marco

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To decode weather satellite data successfully you really need a good antenna. I have done a lot of experimenting and the bottom line is, you need a QFH antenna with a low noise amplifier right at the antenna. Google QFH and you'll find instruction on how to make one for 137MHz. This works. set SDR for WFM and at least 40kHz bandwidth. Experiment. Bob vk2byf

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