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[Discuss-gnuradio] Help to build a loop modulating / de-modulating syste

From: Arturo Rinaldi
Subject: [Discuss-gnuradio] Help to build a loop modulating / de-modulating system
Date: Sun, 15 Nov 2009 21:30:49 +0100
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv: Gecko/20090915 Thunderbird/3.0b4

I'm trying to build this kinda of system for my degree thesis. It is a loop system in the sense its structure could be described in this way

file source (byte) ---> Digital modulator (QAM , PSK , MSK etc) ----> Digital de-modulator -----> File sink (byte)

file source is a text file or a jpeg photo just for example. I read  the de-modulator loses the first 5 bits due to the clock recovery, so i wrote a few lines in python, my steps were :

1) I made a function to read a text file and put its content after converting the single chars in int with the type converter ord( ). Then i put the intS i got  in an array with also adding a byte of empty stuffing as the first one ( a single zero). And putting the content in a byte file source.

2)I connected this byte file source to the modulator (GMSK for example) to get a complex file sink. Then i try to put this last one like complex file source for my de-modulator.

3)The output of the de-modulator is a byte file sink. but i don't get the data i transmitted ! ! ! ! (i.e. the text file doesn't open)

4)I tried a different approach by scanning the complex sink output of 2), converting the contents to int and then putting it in a complex vector to feed the de-modulator. the resulting byte file sink is a text file i can open but i only see the bytes in the text file ! ! ! (the little squares with 1,0 etc)

5)I tried another approach by converting the complex content of the modulator output to int and feeding the intS into a byte file sink. The file  is then scanned and its contents are put as the array arguments of a complex vector. The de-modulator is fed with this complex vector and its output its a byte file sink ( the demodulated one).

in all these cases i don't succeed in get any good de-modulated data (i.e. the original text file or a jpeg photo). where am i wrong ? can i get some hints from anyone of you ?

 thx in advance

@ Richard Clarke

Regarding GNUradio installation on Ubuntu 9.10 i used a little cheat :D. I added the 9.04 repositories to the 9.10  ones and then i was able to install smoothly the DEBs from the gnuradio repository,both  the stable and the un-stable ones. So you also get full dependencies if you want to compile from the git code.

Bye Arturo

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