USRP N210 Signal Phase Issue

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

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

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 7:11 PM, Marcus D. Leech [email protected]
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 L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org


Discuss-gnuradio mailing list
[email protected]
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

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

Matt

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: [email protected]lid
[mailto:[email protected]lid] On Behalf Of
Matt
Ettus
Sent: Wednesday, January 08, 2014 2:25 AM
To: Jonathan F.
Cc: GNURadio D.ion 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 F.
[email protected]
wrote:

On Tue, Jan 7, 2014 at 7:11 PM, Marcus D. Leech [email protected]
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 F.
[email protected]
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
[email protected]
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com


Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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


Discuss-gnuradio mailing list
[email protected]
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

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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