Re: [Discuss-gnuradio] Problem with USRP!

[John Malsbury]

It doesn't matter where you put your antenna...  Ask yourself a 
fundamental question:  When you assign both a receive chain and a 
transmit chain to the same antenna port in a flow-graph, which one gets 
access?  How can you transmit and receive with the same frequency with 
the same antenna without jamming the receiver?  Take the time to 
understand these issues before you do something that will damage the 
receiver LNA's.

Insert a unpacked-to-packed block between your vector source and the 
modulator.  bits per chunk = 1.  See if this produces what you would expect.

I also strongly suggest that you simulate these by looping the output of 
the mod to the input of the demod.  This removes the USRP as a variable 
until you get a better understanding of how these blocks are working.

-John


On 04/08/2012 02:54 PM, huzaifazafar108 wrote:
> Dear John,
>
> Waiting for your response...
>
> And the reason for using TX/RX is that we connected the antennas on TX/RX
> ports on the daughtercard (in both transmitter and receiver).
>
> Thanks,
> Huzaifa
>
>
> John Malsbury wrote:
> > A few more things:
> >
> > 1)  You have both the receive and transmit portions assigned to TX/RX.
> > This only works if you run in half-duplex mode and stop streaming to the
> > USRP.  This is not the case.
> > 2)  Note the difference between sample rate, symbol rate, and bit rate.
> >
> >       symbol_rate = sample_rate / samples_per_symbol
> >       bit_rate = sample_rate/bits_per_symbol
> >
> > I think there are issues with packing/unpacking of bits.  The
> > requirements for packing and unpacking aren't completely consistent
> > across the mod/demods within GNU Radio.  Let me experiment real quick
> > and get back to you.
> >
> > -John
> >
> >
> > On 04/08/2012 02:34 PM, huzaifazafar108 wrote:
> > > Dear Marcus,
> > >
> > > I truly appreciate your prompt reply. However, I am not sure what should
> > > I
> > > put in the 'modulus' field of the block. By hit and trial, wrong outputs
> > > are
> > > emerging. Please guide.
> > >
> > > Best Regards,
> > > Huzaifa
> > >
> > >
> > >
> > > Marcus D. Leech wrote:
> > > > > We just removed the throttle blocks and the same problem remains.
> > > > > Please
> > > > > let
> > > > > us know how to achieve symbol synchronization.
> > > > Well, you're using DPSK, but not using a differential encoder on the TX
> > > > side, nor a differential decoder on the RX side.
> > > >
> > > > > huzaifazafar108 wrote:
> > > > > > Dear John,
> > > > > >
> > > > > > Thank you for such a prompt reply. Okay, we will remove the throttle
> > > > > > blocks just now. But can you guide us how to achieve symbol
> > > > > > synchronization then?
> > > > > >
> > > > > > Best Regards,
> > > > > > Huzaifa
> > > > > >
> > > > > >
> > > > > >
> > > > > > John Malsbury wrote:
> > > > > > > You do not need to use throttles when using a UHD sink/source,
> > > > > > > because
> > > > > > > the device provides timing for the flowgraph.
> > > > > > >
> > > > > > > Remove the throttles and try again.  If you still see the failure I'd
> > > > > > > say you are not achieving symbol sync.
> > > > > > >
> > > > > > > -John
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > On 04/08/2012 01:58 PM, Huzaifa Zafar wrote:
> > > > > > > > Dear all,
> > > > > > > >
> > > > > > > > I am working with 3 people on a project involving GNU Radio and
> > > > > > > > USRP1.
> > > > > > > > We have tried to implement a simple point to point digital
> > > > > > > > communication system in GRC involving DQPSK modulation. Using a
> > > > > > > > vector
> > > > > > > > source we are sending a finite stream of zeros and ones (the vector
> > > > > > > > source has Repeat set to yes). On the receiver side, what we receive
> > > > > > > > is really very strange: The same stream of zeros and ones, but with
> > > > > > > > extra zeros in between our actual data. For example, we send three
> > > > > > > > ones and three zeros, but what we receive is a one followed by seven
> > > > > > > > zeros, another one followed by seven zeros, another one followed by
> > > > > > > > seven zeros, and then a zero followed by seven zeros e.t.c. We tried
> > > > > > > > to experiment more by using the 'KEEP 1 in N' block and the
> > > > > > > > 'DECIMATING FIR FILTER', but things are not working out the way they
> > > > > > > > should.
> > > > > > > >
> > > > > > > > I am also attaching a snapshot of the .grc file for your reference.
> > > > > > > > Please tell us the reason why these extra zeros are present between
> > > > > > > > our data bits, and the way to combat this effect (remember that the
> > > > > > > > decimating fir filter and keep 1 in N block are not showing the
> > > > > > > > desired output). Any kind of help is appreciated in advance.
> > > > > > > >
> > > > > > > > --
> > > > > > > > Huzaifa Zafar
> > > > > > > >
> > > > > > > >
> > > > > > > > _______________________________________________
> > > > > > > > Discuss-gnuradio mailing list
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> > > > > > > _______________________________________________
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> > > > --
> > > > Marcus Leech
> > > > Principal Investigator
> > > > Shirleys Bay Radio Astronomy Consortium
> > > > http://www.sbrac.org
> > > >
> > > >
> > > >
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