[USRP-users] Random long duration noise at the start of UBX captures

Perelman, Nathan nperelman at LGSInnovations.com
Tue Oct 13 13:00:21 EDT 2015


Yes, although the magnitude of the noise appears to decrease as the sample rate decreases:

12.5 MHz - +/- 0.35

6.25 MHz - +/- 0.22

3.125 MHz - +/- 0.15

1.625 MHz - +/- 0.11

It still lasts on the order of 0.4 seconds.

 

I’ve sent you privately a link to data.

-Nathan

 

From: Michael West [mailto:michael.west at ettus.com] 
Sent: Tuesday, October 13, 2015 12:18 PM
To: Perelman, Nathan
Cc: Ben Hilburn via USRP-users
Subject: Re: [USRP-users] Random long duration noise at the start of UBX captures

 

Hi Nathan,

Do you see the effect at lower sample rates?  Can you send me the data file and/or screen capture of the effect you are seeing?

Regards,

Michael

 

On Tue, Oct 13, 2015 at 8:04 AM, Perelman, Nathan <nperelman at lgsinnovations.com> wrote:

Not that I can see. I pasted the full output from the command below. I tried with UHD 3.9.1 and still see the same results.

 

$ /usr/lib64/uhd/examples/rx_samples_to_file --duration 2 --rate 25000000 --freq 1e9 --gain 38 --ref internal --setup 0

linux; GNU C++ version 4.4.7 20120313 (Red Hat 4.4.7-16); Boost_105500; UHD_003.008.005-0-unknown

 

 

Creating the usrp device with: ...

-- Opening a USRP2/N-Series device...

-- Current recv frame size: 1472 bytes

-- Current send frame size: 1472 bytes

Using Device: Single USRP:

  Device: USRP2 / N-Series Device

  Mboard 0: N210r4

  RX Channel: 0

    RX DSP: 0

    RX Dboard: A

    RX Subdev: UBX RX

  TX Channel: 0

    TX DSP: 0

    TX Dboard: A

    TX Subdev: UBX TX

 

Setting RX Rate: 25.000000 Msps...

Actual RX Rate: 25.000000 Msps...

 

Setting RX Freq: 1000.000000 MHz...

-- Successfully tuned to 1000.000000 MHz

-- 

Actual RX Freq: 1000.000000 MHz...

 

Setting RX Gain: 38.000000 dB...

Actual RX Gain: 38.000000 dB...

 

Waiting for "lo_locked": + locked.

 

Press Ctrl + C to stop streaming...

 

Done!

 

From: Michael West [mailto:michael.west at ettus.com] 
Sent: Monday, October 12, 2015 7:07 PM


To: Perelman, Nathan
Cc: Ben Hilburn via USRP-users
Subject: Re: [USRP-users] Random long duration noise at the start of UBX captures

 

Hi Nathan,

I am unable to reproduce what you are seeing.  I have an N210+GPSDO+UBX with a 3A power supply and I ran the rx_samples_to_file command you provided with RX2 terminated and all my data looks clean over multiple runs.  Are you getting any O's, errors, or warnings during your runs?

Regards,

Michael

 

On Mon, Oct 12, 2015 at 2:19 PM, Perelman, Nathan <nperelman at lgsinnovations.com> wrote:

Sorry, forgot to mention that, RX2 is terminated. I am also using a 3 amp power supply not the recommended 4 amp as I don’t have a 4 amp one.

 

I tried setting the reference to internal without disconnecting the GPSDO and then again after disconnecting the GPSDO, and saw the same issue. In the second case, the noise lasted 1.6 seconds, although I don’t suspect the duration has anything to do with the test setup, it seems random.

-Nathan

 

From: Michael West [mailto:michael.west at ettus.com] 
Sent: Monday, October 12, 2015 4:51 PM
To: Perelman, Nathan
Cc: Ben Hilburn via USRP-users
Subject: Re: [USRP-users] Random long duration noise at the start of UBX captures

 

To be clear, when I say disconnect the GPSDO, I mean disconnect the GPSDO power.  The data cables can be left in place.

Regards,

Michael

 

On Mon, Oct 12, 2015 at 1:43 PM, Michael West <michael.west at ettus.com> wrote:

Hi Nathan,

The simple answer is no, that is not expected.  What do you have connected to the RX2 port?  Also, do you see the same effect if you disconnect the GPSDO?

 

Regards,

Michael

 

On Mon, Oct 12, 2015 at 1:26 PM, Perelman, Nathan via USRP-users <usrp-users at lists.ettus.com> wrote:

I’ve been having issues with UBX daughter-boards for a little while, and I finally traced them down to a reproducible issue. Running:

./rx_samples_to_file --duration 2 --rate 25000000 --freq 1e9 --gain 38 --ref gpsdo --setup 0

 

I frequently see large amounts of random noise (up to +/- 0.5 out of 1.0), for up to 0.5 seconds. I have tested with 2 different UBX daughter-boards and seen similar noise. Is this expected with the UBX? I do not see similar noise with the SBX.

 

I am using UHD 3.8.5 with an N210.

-Nathan

 

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