Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 daughter cards

2018-04-20 Thread Stanley, John P. via USRP-users 
Thanks for the insight. Is this publicly documented anywhere? The USRP web 
manual (https://files.ettus.com/manual/page_calibration.html) still explicitly 
states to leave RF ports disconnected for calibration. Updating that page ASAP 
could save folks out there a lot of grief…

From: Michael West <michael.w...@ettus.com>
Date: Thursday, April 19, 2018 at 9:20 PM
To: "Stanley, John P." <john.stan...@jhuapl.edu>
Cc: ROBIN TORTORA <ti...@comcast.net>, "Stanley, John P. via USRP-users" 
<usrp-users@lists.ettus.com>
Subject: Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 
daughter cards

Hi John/Robin:
The calibration utilities rely on leakage across the RF switch.  The newer UBX 
boards (rev C and later) have RF switches with much higher isolation.  The 
benefit is a lot less leakage from TX onto RX.  The drawback is that the 
calibration utilities will only work if you connect the TX/RX to the RX2 port 
with a 30 dB attenuator in line.
Regards,
Michael

On Thu, Apr 19, 2018 at 11:12 AM, Stanley, John P. via USRP-users 
<usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com>> wrote:
While uncalibrated LO leakage has never been great in the UBX for us, the dc 
offset calibration procedure has given us adequate enough improvement.  We’re 
generally using offset tuning, but we still need that extra 15-20 dB 
suppression we get from the calibration procedure.

The issue we’re seeing with these newer Rev C boards, though, is that the 
calibration doesn’t just fail to improve LO suppression; it actively makes it 
worse. Offset tuning is pretty fruitless when the LO spur alone is >0 dBm at 
the mid-point of available RF gain.


From: ROBIN TORTORA <ti...@comcast.net<mailto:ti...@comcast.net>>
Reply-To: ROBIN TORTORA <ti...@comcast.net<mailto:ti...@comcast.net>>
Date: Thursday, April 19, 2018 at 1:44 PM
To: "Stanley, John P. via USRP-users" 
<usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com>>, "Stanley, John 
P." <john.stan...@jhuapl.edu<mailto:john.stan...@jhuapl.edu>>
Subject: Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 
daughter cards


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Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 daughter cards

2018-04-20 Thread The Tilla via USRP-users 
Well, that is super awesome news 

 

Glad you guys made these improvements.

 

How would I know this, I don’t think I have seen this information anywhere?

 

From: Michael West <michael.w...@ettus.com> 
Sent: Thursday, April 19, 2018 9:21 PM
To: Stanley, John P. <john.stan...@jhuapl.edu>
Cc: ROBIN TORTORA <ti...@comcast.net>; Stanley, John P. via USRP-users 
<usrp-users@lists.ettus.com>
Subject: Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 
daughter cards

 

Hi John/Robin:

The calibration utilities rely on leakage across the RF switch.  The newer UBX 
boards (rev C and later) have RF switches with much higher isolation.  The 
benefit is a lot less leakage from TX onto RX.  The drawback is that the 
calibration utilities will only work if you connect the TX/RX to the RX2 port 
with a 30 dB attenuator in line.

Regards,

Michael

 

On Thu, Apr 19, 2018 at 11:12 AM, Stanley, John P. via USRP-users 
<usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com> > wrote:

While uncalibrated LO leakage has never been great in the UBX for us, the dc 
offset calibration procedure has given us adequate enough improvement.  We’re 
generally using offset tuning, but we still need that extra 15-20 dB 
suppression we get from the calibration procedure.

The issue we’re seeing with these newer Rev C boards, though, is that the 
calibration doesn’t just fail to improve LO suppression; it actively makes it 
worse. Offset tuning is pretty fruitless when the LO spur alone is >0 dBm at 
the mid-point of available RF gain. 

 

 

From: ROBIN TORTORA <ti...@comcast.net <mailto:ti...@comcast.net> >
Reply-To: ROBIN TORTORA <ti...@comcast.net <mailto:ti...@comcast.net> >
Date: Thursday, April 19, 2018 at 1:44 PM
To: "Stanley, John P. via USRP-users" <usrp-users@lists.ettus.com 
<mailto:usrp-users@lists.ettus.com> >, "Stanley, John P." 
<john.stan...@jhuapl.edu <mailto:john.stan...@jhuapl.edu> >
Subject: Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 
daughter cards

 


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Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 daughter cards

2018-04-19 Thread Stanley, John P. via USRP-users 
While uncalibrated LO leakage has never been great in the UBX for us, the dc 
offset calibration procedure has given us adequate enough improvement.  We’re 
generally using offset tuning, but we still need that extra 15-20 dB 
suppression we get from the calibration procedure.

The issue we’re seeing with these newer Rev C boards, though, is that the 
calibration doesn’t just fail to improve LO suppression; it actively makes it 
worse. Offset tuning is pretty fruitless when the LO spur alone is >0 dBm at 
the mid-point of available RF gain.


From: ROBIN TORTORA <ti...@comcast.net>
Reply-To: ROBIN TORTORA <ti...@comcast.net>
Date: Thursday, April 19, 2018 at 1:44 PM
To: "Stanley, John P. via USRP-users" <usrp-users@lists.ettus.com>, "Stanley, 
John P." <john.stan...@jhuapl.edu>
Subject: Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 
daughter cards

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Re: [USRP-users] DC Offset Calibration Issue for Rev. C UBX-40 daughter cards

2018-04-19 Thread ROBIN TORTORA via USRP-users 
Hi John,


LO Leakage in general has ALWAYS been a problem for us as well in general on 
the UBX.  The WBX was fine, we migrated to the UBX quite early and had 
significant problems that really were never resolved.  Most of the chatter 
revolved around being continuously in high power mode, but honestly was mostly 
discussions.  Not sure if any actions came out as a result...


Our only mitigation approach was offset tuning, which does work pretty well, 
although this caused us other problems that we had to deal with.

> On April 19, 2018 at 1:32 PM "Stanley, John P. via USRP-users" 
>  wrote:
> 
> 
> I’ve run into an issue with TX LO leakage/DC offset that appears to 
> affect the “Rev. C” hardware version of the UBX-40 daughter cards. When 
> running without any calibration data, LO leakage power is in line with 
> expectations (i.e. about -50 to -45 dBm with 0 dB of RF gain). But if the 
> uhd_cal_tx_dc_offset routine is run, LO leakage actually gets significantly 
> *worse*. When running with the newly generated calibration data, the LO 
> leakage power can get 15-30 dB higher. This is in stark contrast to the 
> behavior seen in older “Ver. B” and “Ver. A” UBX-40 boards, which 
> consistently show a 15-20 dB reduction in LO leakage power.
> 
>  
> 
> I’ve observed this behavior across all 3 Rev. C boards I have checked so 
> far, and I have been unable to reproduce it on any Ver. A or Ver. B boards. 
> I’ve tested different daughter cards across different N210 and N200 main 
> boards and eliminated the main boards as a contributing factor; the behavior 
> follows the stamped hardware revision on the UBX daughter cards.
> 
>  
> 
> I’ve attached a couple signal analyzer screenshots to illustrate the 
> issue. All 4 screenshots come from a UBX-40 board at 0 dB of RF gain being 
> fed with zero-valued samples at 12.5 Msps. The “Ver. B” board goes from about 
> -47 dBm before calibration down to about -69 dBm after calibration. The “Rev. 
> C” board, on the other hand, goes from about -49 dBm before calibration UP to 
> almost -15 dBm after calibration. I’ve observed this general pattern of 
> behavior across at least 2 versions of UHD, though the attached data was 
> generated using UHD 3.11.0.
> 
>  
> 
> Could this be a hardware design issue, a bad production run, or maybe a 
> UHD issue? Has anyone else run into this?
> 
> Thanks,
> 
> John
> 


 

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