Re: [Discuss-gnuradio] Problem receiving square wave

[Francesco B.]

This post is a bit old... but I'm having a similar problem. Created a
modified gr_sig_source_c block such that attributes are assigned by
pseudo-randomly generated numbers (restricted to ranges such as would be
proper, as well as swapping waveform types for integers 0-5 and randomly
assigning one). It compiles and runs. Amplitude and frequency appear to
vary, but sine/cosine waves are the only ones which generate properly. Is
there a known solution to this?

~ Francesco B.


Syed Faisal Shah wrote:
> 
> Hi fellows
> 
> We are trying to transmit and receive train of square wave over
> wireless using RFX 2400. We modified the usrp_siggen.py file
> accordingly to generate square wave. We used
> 
> ./usrp_siggen.py -f 2450M -w 100000
> 
> Is the value with -f option correct? We assume that -f option refers
> to center frequency at antenna but in an  
http://lists.gnu.org/archive/html/discuss-gnuradio/2006-07/msg00097.html 
> earlier post   it was mentioned that it is the DUC frequency. Which
> one is correct?
> 
> On the receiver side, we used usrp_rx_cfile.py script to write the
> received signal samples on a file. The received signal does not look
> like a square wave rather a sinusoid. In some cases, the sinusoid
> appears to be as harmonic of the square wave, sometimes as a modulated
> sinusoid.
> 
> If anyone knows the cause and solution for this problem, please guide us.
> 
> 1. Are we missing anything here? Without communicating with USRP, we
> made sure that gr_sig_source_c.cc (underlying function that
> usrp_siggen.py calls) generates a square wave.
> 
> 2. Do we need to do anything with the USRP tune function? Can we
> specify the IF frequency at the transmitter and receiver explicitly?
> 
> 3. Or we cannot transmit/receive square wave through GNU radio. We
> understand that may be some filters on the usrp board or daughter
> board will not allow high frequency signals that will distort the
> corners of the square wave but getting only a sinusoid does not seem
> right....
> 
> 4. Our ultimate interest is not in square wave. For our purpose, we
> need to generate a shortest possible pulse, say Gaussian pulse,
> transmit it over the air and implement some ranging algorithms. We
> started with square wave and got stuck.
> 
> Any help/ideas will be highly appreciated.
> 
> Thanks
> 
> Faisal
> 
> 
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> 
> 

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