No Digital Modulation Working

[Ahmed Zaheer]

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.

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[sumitstop]

Did you compensate for the LO offset between Tx and Rx ?

[Ahmed Zaheer]

Can you give me any clue how to do that?

Regards.

---

From: sumitstop <[hidden email]>
To: [hidden email]
Sent: Monday, October 22, 2012 9:18 PM
Subject: Re: [Discuss-gnuradio] No Digital Modulation Working

Did you compensate for the LO offset between Tx and Rx ?



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[Josh Blum-3]

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

>
>
> _______________________________________________ Discuss-gnuradio
> mailing list [hidden email]
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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[sumitstop]

Have a look on this http://sumitgnuradio.blogspot.in/2012/10/problem-of-frequency-offset.html

[senthil murugan]

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.
>

Hi,

If things are working fine for FM modulation,then it's surely due to LO offset between Tx & Rx. I hope

you know on how to correct LO offset. 

Sumit: If possible, could you please post some videos and tutorials on LO Offset Correction. 

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[sumitstop]

Yeah ..Done already

[Sakib Chowdhury]

Apart from what everyone said, what I can see from your attached file is that you are multiplying with 5000 before sending to USRP sink, isn't it? There is possibly a clipping issue here. Also in the receiver side, you should remove the throttle. Throttle is needed only when there is no hardware involved. If any hardware (such as USRP, audio source/sink) is involved in your flowgraph you don't need throttle.

On Tue, Oct 23, 2012 at 10:58 PM, sumitstop <[hidden email]> wrote:

Yeah ..Done already



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[Ahmed Zaheer]

Thanks Sakib, the issue was solved when I changed the multiplying constant to 100 mili. They were not communicating due to clipping. 

Regards.

Ahmed.

---

From: Sakib Chowdhury <[hidden email]>
To: [hidden email]
Cc: [hidden email]
Sent: Wednesday, October 24, 2012 8:43 AM
Subject: Re: [Discuss-gnuradio] No Digital Modulation Working

Apart from what everyone said, what I can see from your attached file is that you are multiplying with 5000 before sending to USRP sink, isn't it? There is possibly a clipping issue here. Also in the receiver side, you should remove the throttle. Throttle is needed only when there is no hardware involved. If any hardware (such as USRP, audio source/sink) is involved in your flowgraph you don't need throttle.

On Tue, Oct 23, 2012 at 10:58 PM, sumitstop <[hidden email]> wrote:

Yeah ..Done already



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