Differences

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--- gnuradiotips [2021/08/25 23:54] – mm3iig
+++ gnuradiotips [2021/09/13 22:27] (current) – [Using Baseband I/Q Recordings] mm3iig
@@ Line 9: / Line 9: @@
 ===== Using Baseband I/Q Recordings =====
-Depending on the specifics of your recording you may need to change bits of this. You’ll want to use a WAV file sync, set the channels to two, and then immediately convert from float to complex to do useful things with the data. Then you’ll want a throttle block to set your desired sample rate. If you have recordings in a format other than 16-bit stereo you may need to add extra conversion steps, or convert your input file first with other software.
+Depending on the specifics of your recording you may need to change bits of this. You’ll want to use a WAV file sync, set the channels to two, and then immediately convert from float to complex to do useful things with the data. Then you’ll want a throttle block to set your desired sample rate. If you have recordings in a format other than RIFF 16-bit stereo you may need to add extra conversion steps into your flowgraph, or convert your input file first with other software.
-If your chosen signal is in the middle of the baseband, you’re done! If it isn’t, you will need to “tune in” to the signal with a Frequency Xlating FIR or FFT Filter first.
+One thing you will have to look out for is the 4 GB wav file size limit in GNU Radio. WAV File Source blocks use the metadata of the file which can only store a maximum value of of 4 GB in its 32-bit size variable. Other apps can store more in a WAV container by reading file size information directly via the operating system, and typically ignore any useful data in the header. Apps that support this include SDR Console and SDR++
+To get around this you can use a tool such as sox to chop up your file into smaller chunks. You can estimate using different times and see if you get the chunk sizes you want - the following command will continue to make chunks of the chosen mm:ss length until there’s no more data and iterate a number after the outfile name:
+**sox --ignore-length infile.wav outfile.wav trim 0 mm:ss : newfile : restart**
+For RF64 WAV files you can use a File Source followed by an iShort to Complex to effectively skip the header and send out valid data.
+If you’ve got the opposite issue - a bunch of smaller basebands that need joining together, you can try:
+**sox --ignore-length infile1.wav ... infile[n].wav outfile.wav**
+After all of that: if your chosen signal is in the middle of the baseband, you’re done! If it isn’t, you will need to “tune in” to the signal with a Frequency Xlating FIR or FFT Filter first.
 ===== Adding, Subtracting, and Multiplying Signals =====
@@ Line 23: / Line 34: @@
 ===== Working with bits and bytes =====
-To follow. Some basic advice for digital signals on how to actually convert from bytes to signals you can modulate, and how to go from a stream of demodulates bits to something your computer can do things with.
+To follow. Some basic advice for digital signals on how to actually convert from bytes to signals you can modulate, and how to go from a stream of demodulated bits to something your computer can do things with.
 ===== Useful Flowgraphs =====
-Add a list of useful GRCs with explanatory text here. You can build your own projects off these.
+Add a list of useful GRCs with explanatory text here. You can build your own projects off these basic ideas.
 To be added:
@@ Line 35: / Line 46: @@
   * NFM Modulation
   * NFM Demodulation
+  * WFM Stereo Modulation
+  * WFM Stereo Demodulation
   * QPSK Modulation
   * QPSK Demodulation
   * BPSK Modulation
   * BPSK Demodulation