Re: [Discuss-gnuradio] No Digital Modulation Working

[Josh Blum]

On 10/22/2012 03:03 PM, Ahmed Zaheer wrote:
> Hi all, I was trying to make a transceiver working on any digital
> modulation. I have tried GMSK, PSK, QPSK, QAM and other blocks
> available in gnuradio companion. But non of them works. All of them
> works in loop back manner but when ever I try to transmit and receive
> on air it simply doesn't work. In the attached file I am using GMSK
> while transmitting a video file. I have also tried audio file, and
> even a simple sine wave but all in vain. I am using USRP N210 with
> SBX daugherboard with VERT 2450 antenna. All of the equipment works
> as I was succeeded in transmitting my voice while doing frequency
> modulation. If anybody can tell me about any mistake while seeing the
> attached file or provide me with any transceiver using any digital
> modulation which should work on latest gnuradio with USRP N210 that
> would really be a great help. I really appreciate your help. 
> Regards. Ahmed.
> 

One issue is that all the TX samples are clipping.
You actually want a transmit amplitude < 1.0

-josh

PS this project may also interest you:
https://github.com/buoyboy/pre-cog

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