Forum: GNU Radio USRP N210 Signal Phase Issue

Afbb56f25f6c6a2d88882cd10606d791?d=identicon&s=25 Jonathan Fox (Guest)
on 2014-01-08 00:04
(Received via mailing list)
Attachment: normal.GIF (20 KB)
Attachment: odd.GIF (20 KB)
A colleague and I are sending a simple signal in GNU Radio (sine wave, 1
MHz, amplitude of 1) to the USRP sink and have the center frequency at
500
MHz. The N210 USRP is hooked up to an Agilent spectrum analyzer. On the
analyzer we are seeing a weird phenomena every two seconds. At first we
see
the carrier frequency and two sidebands from the sine wave (see attached
normal.gif). Then after two seconds we get two bursts of multiple
harmonics
(see odd.gif).

The question is, why is this happening? Does the phase of the 1 KHz
signal
become discontinuous before or after being sent to the USRP?

Thanks,

Jon Fox
3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2014-01-08 00:30
(Received via mailing list)
Try reducing the amplitude to 0.7.  Another possibility is that your
computer can't keep up.  If you are using one of the standard programs,
are
there U's printing in the terminal?

Matt
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2014-01-08 01:13
(Received via mailing list)
>
> Try reducing the amplitude to 0.7.  Another possibility is that your
> computer can't keep up.  If you are using one of the standard
> programs, are there U's printing in the terminal?
>
> Matt
>
Also, what RF gain are you setting?  Does it exceed the maximum input
level of the spectrum analyser?

Are you connected directly, or with an antenna?
Afbb56f25f6c6a2d88882cd10606d791?d=identicon&s=25 Jonathan Fox (Guest)
on 2014-01-08 02:19
(Received via mailing list)
On Tue, Jan 7, 2014 at 7:11 PM, Marcus D. Leech <mleech@ripnet.com>
wrote:

> Are you connected directly, or with an antenna?
>> normal.gif). Then after two seconds we get two bursts of multiple harmonics
>> USRP-users mailing list
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> Discuss-gnuradio@gnu.org
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>


I don't recall seeing any U's but I can recheck tomorrow. The gain on
the
USRP was set to -2. The USRP was connected directly with an SMA cable.
The
analyzer is an Agilent E4440A, the Analyzer is rated for at least 1 Watt
on
average, 100 Watt on a peak pulse (with the built-in attenuator in use).
While I am not ruling out the maximum input I thought the N210 tops out
at
0.5 Watts due to FCC regulations.

Thanks

Jon
3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2014-01-08 02:27
(Received via mailing list)
It could be the usrp digitally clipping, not the analyzer.

Matt
0c86c3b09550eaad22e8a35a3a189672?d=identicon&s=25 Ralph A. Schmid, dk5ras (Guest)
on 2014-01-08 10:28
(Received via mailing list)
May it be just some lost packet or smth. like that? It looks very
similar
when USB does not catch up when using my USRP1 and BladeRF... Missing
samples can create funny signals.



Ralph.





From: discuss-gnuradio-bounces+ralph=schmid.xxx@gnu.org
[mailto:discuss-gnuradio-bounces+ralph=schmid.xxx@gnu.org] On Behalf Of
Matt
Ettus
Sent: Wednesday, January 08, 2014 2:25 AM
To: Jonathan Fox
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] [USRP-users] USRP N210 Signal Phase
Issue





It could be the usrp digitally clipping, not the analyzer.



Matt



On Tue, Jan 7, 2014 at 5:17 PM, Jonathan Fox
<31fox@cardinalmail.cua.edu>
wrote:

On Tue, Jan 7, 2014 at 7:11 PM, Marcus D. Leech <mleech@ripnet.com>
wrote:



Try reducing the amplitude to 0.7.  Another possibility is that your
computer can't keep up.  If you are using one of the standard programs,
are
there U's printing in the terminal?



Matt



Also, what RF gain are you setting?  Does it exceed the maximum input
level
of the spectrum analyser?

Are you connected directly, or with an antenna?







On Tue, Jan 7, 2014 at 3:03 PM, Jonathan Fox
<31fox@cardinalmail.cua.edu>
wrote:

A colleague and I are sending a simple signal in GNU Radio (sine wave, 1
MHz, amplitude of 1) to the USRP sink and have the center frequency at
500
MHz. The N210 USRP is hooked up to an Agilent spectrum analyzer. On the
analyzer we are seeing a weird phenomena every two seconds. At first we
see
the carrier frequency and two sidebands from the sine wave (see attached
normal.gif). Then after two seconds we get two bursts of multiple
harmonics
(see odd.gif).



The question is, why is this happening? Does the phase of the 1 KHz
signal
become discontinuous before or after being sent to the USRP?



Thanks,



Jon Fox


_______________________________________________
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users...




_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio






--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org


_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio



I don't recall seeing any U's but I can recheck tomorrow. The gain on
the
USRP was set to -2. The USRP was connected directly with an SMA cable.
The
analyzer is an Agilent E4440A, the Analyzer is rated for at least 1 Watt
on
average, 100 Watt on a peak pulse (with the built-in attenuator in use).
While I am not ruling out the maximum input I thought the N210 tops out
at
0.5 Watts due to FCC regulations.



Thanks

Jon
Afbb56f25f6c6a2d88882cd10606d791?d=identicon&s=25 Jonathan Fox (Guest)
on 2014-01-08 22:58
(Received via mailing list)
It works now, although with some U's on the console, they were there
before
anyways. I forgot to run systctl -w net.core.rmem_max=50000000 and
net.corewmem_max=1048576. As soon as I ran it the harmonics went away.
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