3

I am new to GNU Radio, so I am learning through simple projects. I have a .txt file that I want to receive in another .txt file by sending and receiving the file through PSK Mod and Demod modules (no SDR yet).Therefor I made the following flow graph:

File Source ----> PSK Mod ----> PSK Demod ----> Throttle ----> File Sink

I chose Num._of_Const. to be 4, and chose the path for the source file and sink file. I also set the output type of the source file (and the input type of the sink file) to be 'bytes'. When I run the grc file, something is being stored in the sink file. However, when I read it, the sink file seems to contain some random symbols and numbers that completely do not match the text that was supposedly sent from the source file.

I have read online that some people use the block Unpacked_to_packed but that did not work for me either. I am trying to begin with simple projects, but I feel I am missing on something, so your help would be much appreciated.

Marcus Müller
  • 34,677
  • 4
  • 53
  • 94
Doe
  • 185
  • 3
  • 13

1 Answers1

3

as the PSK demod contains some control loops to synchronize to a frequency/timing offset, it might just be missing the first few bits, even if you parameterized the blocks completely correctly. That will lead to your output bitstream being shifted by a few bits, and then the byte boundaries do no longer match, and you're getting garbled data. You should still be seeing the right sequence of bits, if you looked at your RX file in binary, instead of as text.

You will need to correct that offset by finding a "known" bit sequency. Essentially, you need any kind of "framer", so that you know when a byte boundary happens.

Also, PSK demod has documentation that clearly states it gives you unpacked data, i.e. one bit per output byte; you will need a unpacked_to_packed to get your original bytes.

PS: please don't use "random" unrelated tags. You're not using an USRP here, neither are you using LISP nor is this related to the GNU "overproject". All tags (should) have descriptions, and you should only use a tag if you're sure it applies to your problem
Marcus Müller
  • 34,677
  • 4
  • 53
  • 94