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I recorded some transmitted data using the Noo-Elec RTL2832 software-defined radio. The data is transmitted at a carrier frequency of 1.3GHz and sampled at 2.4MHz. The transmitted data is a set of line codes, each linecode starts with an ASCII space and is followed by 21 ASCII characters with short spaces between linecodes. I imported the raw 8 bit IQ data into python and split up each burst of data into seperate arrays to begin classifying each linecode individually. The IQ samples are converted to complex samples \$I +jQ\$ for ease of use. These complex samples are stored in a single column python list data type. The first plot shows the real component of the line code plotted against time, the second shows the phase plotted against time (I have applied an unwrapping algorithm to it) and the last is the power spectral density against frequency. I'm having trouble identifying the following two line codes:

unknown linecode 1

unknown linecode 2

How can I use this data to make an informed decision about what these line codes are?

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What you need is to plot the I and Q values out to decide what kind of encoding scheme the transmitter used.

This can be done by using plot(I,Q) or scatter(I,Q) for whatever data you have. You should get a plot kind of like the ones below, but with noise added.

enter image description here Source: https://www.researchgate.net/publication/228380492_conceptual_background_to_radio/figures?lo=1

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  • \$\begingroup\$ Is the modulation scheme different from a linecoding? I plotted the constellation graph for each linecode and got the same thing for all of them - a concentration of dots around 0 and then a larger ring of dots around 1. \$\endgroup\$ – Blargian Aug 31 '18 at 18:49

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