Re: [Discuss-gnuradio] Problem DPSK Mod/ Demod - UHD USRP1 Blocks

[Tom Rondeau]

On Fri, Apr 20, 2012 at 12:07 PM, Javier Suarez <address@hidden> wrote:
> Good morning,
>
> I am working in digital communications specifically with dpsk modulation in
> gnu radio.
> I  made a very simple dpsk modulation and demodulation testing flow graph .
> this is the flow graph that I made for the transmitting part:
>
> https://picasaweb.google.com/101968292957887487468/DQPSKMODULATION#5733510080875799138
>
> And the transmitted spectrum, before the UDH USRP1 sink block  is :
>
> https://picasaweb.google.com/101968292957887487468/DQPSKMODULATION#5733510073889925042
>
> And for the receiver I did this:
>
> https://picasaweb.google.com/101968292957887487468/DQPSKMODULATION#5733510072472332802
>
> I receive this spectrum after the UHD-USRP1 source block:
>
> https://picasaweb.google.com/101968292957887487468/DQPSKMODULATION#5733510074110374626
>
> I hope to see any spectrum there! Also I hope to see a kind of cosine signal
> in the scope at the final of the flow graph but I see nothing!

Use the uhd_siggen and uhd_fft to make sure you're systems are both
transmitting and receiving. It's likely that you aren't transmitting
enough power, have the antenna on incorrectly, or something else. Use
the debug tools we provide to understand your RF setup.

> I dont know what I am doing wrong.  I am transmitting 16 samples/symbol with
> a symbol rate of 125 ksymbols/seg which is equal to a sample rate  of  2
> Msamples/s at the  TX and RX UHD - USRP block.The center frequency of the
> UHD-USRP1 block was set at 2.4 GHz because the daughter board is a RFX 2400.
>
> Also  when I run this program, I can see in the terminal :
>
> UOUOOUOUOUOUOUOUOUOUOUOUOUOUOUOUOUOUOUOUO

These are explained in many mailing list questions as well as on our
wiki. It's indicating overruns and underruns. Basically, your computer
isn't keeping up. Try using a rate less than 2 Msps.

> Please, I hope anyone can help me. I have working on this for a long time
> and I dont know what else to do. Thanks!!

Hope this helps.

Tom