HFU HF Underground
Technical Topics => SDR - Software Defined Radio => Topic started by: ChrisSmolinski on May 17, 2016, 1952 UTC
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I've released version 0.2.0 of mySdrPlayback, an app that lets you quickly go through I/Q recording files made by software for RF Space and Perseus SDRs. (I personally use SdrDx: http://fyngyrz.com/?p=915 although SpectraVue produces the same format files) mySdrPlayback is free, and available for Mac OS X 10.6 and later. You can download a copy of the app here: http://www.blackcatsystems.com/software/sdr_iq_recording_playback_program.html
It makes it easy to slog through lots of recording files, looking for intresting signals. Load a file, and a waterfall for the entire file is created. You can scroll around, and if you see anything that looks interesting, you can drag select it, and then demodulate it. You can even save the demodulated audio as a WAVE file, that you can listen to later, send to someone else, or play into your digital decoding software, if it is an RTTY, SSTV, etc. transmission.
The major change to this version is to allow you to change the size of the FFT that is performed on the I/Q data, used to draw the waterfall. I wanted to improve the detectability of very weak transmissions. Here are some before and screenshots.
This waterfall shows two transmissions from May 15th on 6925 and 6935 USB, at 0332 and 0334 UTC respectively. See them? You barely can, if you know they are there. And squint a lot:
(http://i.imgur.com/P7C89TU.png)
Now here is a waterfall from the same recording file, this time with a longer FFT time, 65536 samples, vs the default 8192 samples. Much easier to spot the transmissions:
(http://i.imgur.com/aEqgrPH.png)
You can also spot three short ALE transmissions. They were visible before, but are much more clear now. My hope is this change will let me spot more bumps in the night.
This version also adds a button to generate timestamped WAVE audio files from the demodulation (I got tired of re-naming the files by hand). It also displays an audio spectrum when you demodulate in WFM (Wide FM mode), showing the various subcarriers on an FM station:
(http://www.blackcatsystems.com/pics/mysdrplayback_wide_fm_spectrum.png)
Will I add demodulation of subcarriers and RDS? Maybe. We'll see ;D
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Very nice work, I've found that increased fft samples can indeed show a much more detailed spectra, such as the individual tones in a S4285 signal. The trade off is response time of the display and perhaps increased cpu time for the app, but worth it if you want to really see what the signal looks like.
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How about AM Stereo (C-QUAM)? :o
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How about AM Stereo (C-QUAM)? :o
I've wanted to demodulate that, for XFM. I have yet to find enough technical information (or better yet sample code) to be able to do so, however.