[USRP-users] [Discuss-gnuradio] New UHD seems to break a lot...

Ian Buckley ianb at ionconcepts.com
Mon Apr 20 14:05:10 EDT 2015


To close the loop on this thread, 3.8.3-RC1 has a bug in new code that automatically calculates master_clock_rates when they are not explicitly stated. This specifically affects B2x0 and E3x0 since they are AD9361 based with a very flexible master_clock_rate. In this case Ralph asked for a sample_rate of 9.142857 MHz and UHD erroneously forced a master_clock_rate of 8MHz. An explicit master_clcok_rate request (in this case for 9.142857MHz) works around the bug as shown (green without, yellow with): http://ianbuckley.net/ralph_spectrum.jpg. The master_clock_rate override does print a warning in the UHD log so you can see that this is happening:

UHD Warning:
    The hardware does not support the requested TX sample rate:
    Target sample rate: 9.142857 MSps
    Actual sample rate: 8.000000 MSps

There is also another bug in RC1 that also prints incorrect warnings. Warnings of this form can currently be ignored until this is fixed should you know that you have actually set sensible sample_rates:

UHD Warning:
    The requested decimation is odd; the user should expect CIC rolloff.
    Select an even decimation to ensure that a halfband filter is enabled.
    decimation = dsp_rate/samp_rate -> 37 = (9.142857 MHz)/(0.250000 MHz)

NOTE: Ralph, your flow graph used a TX gain of 99…this is way too high for the signal being driven to the USRP, you were driving the output amp into saturation.
-Ian

On Apr 18, 2015, at 12:24 AM, "Ralph A. Schmid, dk5ras" <ralph at schmid.xxx> wrote:

> Yes, I can confirm hash 2fe3..., and the images were downloaded with the supplied uhd_image_downloader, what is configured like this:
>  
> _DEFAULT_BASE_URL         = "http://files.ettus.com/binaries/images/"
> _AUTOGEN_IMAGES_FILENAME  = "uhd-images_003.008.003-rc1.zip"
> _AUTOGEN_IMAGES_CHECKSUM  = "8522b02386f5fe0bb51baa3ba0001ef0"
>  
> The GRC filkes are accessible now, the only modifications I made were due to Ron Economos' hints regarding sampling rate, and I added a frequency slider to choose the correct European TV channel without having to know the frequency.
>  
> Ralph.
>  
>  
> From: Ian Buckley [mailto:ianb at ionconcepts.com] 
> Sent: Saturday, April 18, 2015 03:45
> To: Ralph A. Schmid, dk5ras
> Cc: 'Martin Braun'; usrp-users at lists.ettus.com; 'GNU Radio Discussion List'
> Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
>  
> Ralph,
> I'm not able to access either of the .grc files on your website, but using the original dvbt_tx_demo_8k flow graph from gr-dvbt, the spectrum I generate with 003.008.003-RC1 has a 3dB bandwidth of about ~7.5MHz the same as your uhd_master screen shot. I don't see the truncated bandwidth of your uhd_rc1 screenshot. http://ianbuckley.net/dvbt.jpg
> Can you verify please that you have UHD at the current 003.008.003-RC1 tag position git hash 2fe319d9790c7ec0bcdb9582c4fea95f3fd809b9, and that the downloaded FPGA images are from: http://files.ettus.com/binaries/images/uhd-images_003.008.003-rc1.zip
>  
> I'll need your exact flow graph if I'm to debug this anymore.
>  
> -Ian
>  
>  
>  
> On Apr 17, 2015, at 11:48 AM, "Ralph A. Schmid, dk5ras" <ralph at schmid.xxx> wrote:
> 
> 
> I have put it all here, flow graphs and screenshots of the flow graphs:
> 
> http://dk5ras.dyndns.org/tmp/DVB/
> 
> This way we can keep it on the list without sending attachments.
> 
> They were taken from the VM container before all the upgrades were made, but
> I did not change anything when upgrading.
> 
> Ralph.
> 
> 
> 
> -----Original Message-----
> From: Ian Buckley [mailto:ianb at ionconcepts.com] 
> Sent: Friday, April 17, 2015 19:25
> To: Ralph A. Schmid, dk5ras
> Cc: 'Martin Braun'; usrp-users at lists.ettus.com; 'GNU Radio Discussion List'
> Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
> 
> Great Ralph, thats a big help. Can you send me your exact flow graph used to
> generate these 2 plots off list please. I want to re run this scenario and
> see your exact configuration.
> 
> Thanks
> -Ian
> 
> On Apr 17, 2015, at 10:00 AM, "Ralph A. Schmid, dk5ras" <ralph at schmid.xxx>
> wrote:
> 
> 
> OK, here we go. The hotel TV was dvb-c only, so I had to do the tests 
> back at home.
> 
> I took my perfectly working Kubuntu 14.04 64 bit VM container together 
> with my B210, made a copy and updated this one, first I made a git 
> pull to get latest master, built it, rebuilt gnuradio, rebuilt 
> gr-dvbt, updated the FPGA images, and everything still was fine. The
> chosen dvb-t bandwidth is 8 MHz.
> 
> 
> Then I changed to 003_008_003_rc1, did the same procedure, fired up 
> grc, and the signal was not decodable both with a dvb-t PC receiver 
> and with an dvb-x analyzer. The analyzer saw the RF level, but no 
> data, no constellation, nothing, it looked to him like interference.
> 
> When you have a look at the two "uhd" screenshots here 
> http://dk5ras.dyndns.org/tmp/DVB/ made with my spectrum analyzer then 
> you will find that RC1 produces a somehow narrower signal, so it 
> really looks something gets cut at the ends with all the filtering and DSP
> stuff.
> 
> Adjusting the channel bandwidth in the uhd sink block from 0 to a 
> sensible value changes nothing.
> 
> Btw., the dvb-t2 package behaves identical.
> 
> Ralph.
> 
> 
> -----Original Message-----
> From: Martin Braun [mailto:martin.braun at ettus.com]
> Sent: Wednesday, April 15, 2015 21:14
> To: Ralph A. Schmid, dk5ras; usrp-users at lists.ettus.com; 'GNU Radio 
> Discussion List'
> Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
> 
> master works, but RC1 does not? Huh, I'm confused now. Can you give 
> some detail on what's going on, so we can try and reproduce this?
> 
> Thanks,
> Martin
> 
> On 15.04.2015 12:52, Ralph A. Schmid, dk5ras wrote:
> 
> RC1, master seems to work.
> 
> Ralph.
> 
> -----Original Message-----
> From: Martin Braun [mailto:martin.braun at ettus.com]
> Sent: Wednesday, April 15, 2015 15:44
> To: Ralph A. Schmid, dk5ras; usrp-users at lists.ettus.com; 'GNU Radio 
> Discussion List'
> Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
> 
> Thanks, Ralph. Just to clarify: When you say 'New UHD', do you mean 
> 3.8.3-RC1, or latest master?
> 
> Martin
> 
> On 15.04.2015 08:40, Ralph A. Schmid, dk5ras wrote:
> 
> It is a B210, but as a note, due to the up to now missing FPGA 
> images I used 003.008.003-RC1, not the latest master. Still I had no 
> access to a spectrum and DVB-T analyzer, so I have no idea what is 
> happening, I just can confirm that RF is transmitted, and the 
> receiver doesn't get a picture, while with the snapshot of the same 
> VM before the upgrade
> is received without problems.
> 
> I will know more in about three hours.
> 
> Ralph.
> 
> 
> -----Original Message-----
> From: Martin Braun [mailto:martin.braun at ettus.com]
> Sent: Wednesday, April 15, 2015 3:15 PM
> To: Ralph A. Schmid, dk5ras; usrp-users at lists.ettus.com; 'GNU Radio 
> Discussion List'
> Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
> 
> On 15.04.2015 06:20, Ralph A. Schmid, dk5ras wrote:
> 
> Hi,
> 
> Not only OpenBTS is affected, also gr-dvbt/t2 do not work any more 
> with latest uhd. A quick check during lunch break showed, the 
> produced output is not decodable any more. I will take a closer 
> look this evening at home, where I have more and better equipment.
> 
> Ralph,
> 
> which device is this on?
> 
> Thanks,
> Martin
>  
>  
> 
>  
> 
>  
> 
>  

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