2/23/2023 0 Comments 4 byte bit slicer![]() One thing to notice is that the M&M usually works on complex samples, so you need to change the sample type to float. ![]() Its easy to use and since the singnal does not have much noise on it, it will work perfectly. There are several blocks that can do that, but I usually prefer the M&M Clock Recovery block. After that we need something to synchronize our bits and find where to sample the bits we want. I selected the option Repeat to be false, so it will not run foverer repeting the file. In GNU Radio the first thing we should do is get a Wav File Source to open the file: So now we have enough information then we can go to GNU Radio! Since the wav sample rate is 32000 we can expect the baudrate to be something close to 8000. Then you can see that there is 4 samples selected (just check these dots, they’re the samples in the file) which means that there is 4 samples per bit in the wav signal. I got one negative and one positive short peak, which would represent a 0 to 1 transition or a 1 to 0 transition. That’s probably the minimum period of the signal which usually tells us a bit change. Just find two peaks that are closer to each other than other any other. That can be done manually in the audacity itself. We can use GNU Radio to transform that in a bitstream, but before we need to know the baud rate (or bit rate). The 0 is usually the transistion, and in a 2-FSK 1 and -1 represents the bits itself. I said 2-FSK besides other ones, because there is clearly almost only three values there: 1, 0 and -1. When you demodulate a 2-FSK I/Q from correctly from a Radio, it will convert the frequency to voltage leading to a pattern like the one saw. ![]() ![]() That looks like a 2-FSK demodulated file (see ). If we open in audacity we will se a very interesting pattern: The zip file itself contains a wav file which they told us is not an audio but an radio signalįile command to show what the wave file is And everyone that knows me know that I love SDR stuff. I got really excited about it because its a SDR one. ![]()
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