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[Discuss-gnuradio] [ input ] -> [ PSK mod ] -> [ PSK Demod ] -> [ output

From: abdullah unutmaz
Subject: [Discuss-gnuradio] [ input ] -> [ PSK mod ] -> [ PSK Demod ] -> [ output ] => [ input ] != [ output ] - interesting
Date: Wed, 15 Aug 2012 03:10:13 -0700 (PDT)


In gnuradio-companion I connected output of a "PSK Mod" directly to a "PSK Demod" input. Both of the blocks have the same initializations,

Number of Constellation Points:2
Gray Code:Yes
Differential Encoding:No
Excess BW:350m

in PSK Demod other properties are as follows:

Frequency BW:62.8m
Phase BW=62.8m

The output of the PSK Demod is fed into "UHD:USRP Sink" with a zero center frequency after applying some type conversion blocks, "UChar To Float" &
"Float To Complex". I connect an external oscilloscope, i.e. not in PC, not a GRC block a real one, to the output of the USRP to observe what I have after appyling PSK mod and demod. As the output of the process, I have a completely different signal from I generated in the beginning.

I also checked what happens if I directly feed the actual signal to the "UHD:USRP Sink", I got a signal nearly same as the original one, that is as expected, great.

Another surprising thing, when I apply the output of the "PSK Mod" to the "UHD:USRP Sink" and observe the output of the USRP1 output, constellation points number is 2, although I see BPSK format, 180 degree phase shift in the signals as I expected, I see 100 kHz baseband signal frequency converts into 62.42 kHz, oscilloscope says so :), Samples / Symbol rate is 8.

What might be the problem?


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