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Re: [Discuss-gnuradio] [ input ] -> [ PSK mod ] -> [ PSK Demod ] -> [ ou

From: Josh Blum
Subject: Re: [Discuss-gnuradio] [ input ] -> [ PSK mod ] -> [ PSK Demod ] -> [ output ] => [ input ] != [ output ] - interesting
Date: Wed, 15 Aug 2012 08:34:59 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120714 Thunderbird/14.0

If this helps, the psk mod inputs packed bytes, however the demod
outputs unpacked bytes, where each byte is a decoded symbol. Obviously
you need some kind of framer correlate to reconstruct the packed byte
boundaries outside of the demod. It might be more comparable to use a
unpacked to packed block before the demod. That way both input and
output data is unpacked.


On 08/15/2012 03:10 AM, abdullah unutmaz wrote:
> Greetings,
> 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 Samples/Symbol:8 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?
> Thanks, Abdullah
> _______________________________________________ Discuss-gnuradio
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