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Re: [Discuss-gnuradio] New UHD seems to break a lot...

From: Ian Buckley
Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
Date: Mon, 20 Apr 2015 11:05:10 -0700

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.

On Apr 18, 2015, at 12:24 AM, "Ralph A. Schmid, dk5ras" <address@hidden> 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.
From: Ian Buckley [mailto:ianb@ionconcepts.com] 
Sent: Saturday, April 18, 2015 03:45
To: Ralph A. Schmid, dk5ras
Cc: 'Martin Braun'; address@hidden; 'GNU Radio Discussion List'
Subject: Re: [Discuss-gnuradio] New UHD seems to break a lot...
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.
On Apr 17, 2015, at 11:48 AM, "Ralph A. Schmid, dk5ras" <address@hidden> wrote:

I have put it all here, flow graphs and screenshots of the flow graphs:


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.


-----Original Message-----
From: Ian Buckley [mailto:address@hidden] 
Sent: Friday, April 17, 2015 19:25
To: Ralph A. Schmid, dk5ras
Cc: 'Martin Braun'; address@hidden; '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.


On Apr 17, 2015, at 10:00 AM, "Ralph A. Schmid, dk5ras" <address@hidden>

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

Adjusting the channel bandwidth in the uhd sink block from 0 to a 
sensible value changes nothing.

Btw., the dvb-t2 package behaves identical.


-----Original Message-----
From: Martin Braun [mailto:address@hidden]
Sent: Wednesday, April 15, 2015 21:14
To: Ralph A. Schmid, dk5ras; address@hidden; '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?


On 15.04.2015 12:52, Ralph A. Schmid, dk5ras wrote:

RC1, master seems to work.


-----Original Message-----
From: Martin Braun [mailto:address@hidden]
Sent: Wednesday, April 15, 2015 15:44
To: Ralph A. Schmid, dk5ras; address@hidden; '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?


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.


-----Original Message-----
From: Martin Braun [mailto:address@hidden]
Sent: Wednesday, April 15, 2015 3:15 PM
To: Ralph A. Schmid, dk5ras; address@hidden; '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:


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.


which device is this on?






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