usrp-users@lists.ettus.com
Discussion and technical support related to USRP, UHD, RFNoC
View all threadsunstable LO of USRP-N200 and WBX
Hi all,
I'm currently using a USRP N200 with a WBX daughterboard. We are using a
gnuradio design (with some custom blocks) to synchronize the LOs of several
USRPs to the LO of a master USRP using over-the air-signals.
While the setup was working perfectly with our old USRP-2, I have some
problems for it to work with the USRP-N200. The LOs of the latter seems to
sometimes randomly "jump" by several tens of Hz.
Even more surprising, when I untightened some of the bolts of the WBX
daughterboard, the LO of the USRP-N200 became much more stable.
Is it possible that there is some short-circuit or some mass problem between
the daughterboard and the USRP board, which would cause the LO to be fairly
unstable? Has anyone encountered this problem before?
Thanks for your help,
Francois
Hi all,
i want to use 2 x (N210 + SBX) for a laser telemetry application.
i need to synchronize clocks, align sample times and also have precise knowledge
of LO phase difference between both N210s.
At the moment, using a mimo cable, i use the following
method : i generate a 1.00005 GHz and inject it on both N210s
with a center frequency equal to 1 GHz.
I get 2 exact 50 kHz complex signals with a constant phase difference. Each time
i start a measure, i get an other phase difference, still constant.
if i change the frequency from 1 GHz to 1.1 GHz then go back
to 1 GHz, the phase difference has changed.
I can't use this for a telemetry application.
i have read this application note :
http://www.ettus.com/content/files/kb/Selecting_an_RF_Daughterboard.pdf
and find this :
Do I plan to implement beamforming or direction finding (DF) capability?
While all daughterboards can be used in a MIMO configuration, this does not necessarily imply there is phase alignment between the RF chains of one or more daughterboards. The BasicRx, BasicTX, LFRX and LFTX are exceptions to this, since they do not include local oscillators that contribute to phase ambiguity between channels.
The Ettus Research SBX daughterboard utilizes an RF PLL that includes a resynchronization feature, which can be used to align the LOs across multiple SBXs, and multiple USRP hardware devices. Using the
UHD (USRP Hardware DriverT), timed SPI commands can drive this re-synchronization feature. At the time of this writing, this feature is not supported in the mainline UHD. However, this feature is planned for release in 2012.
I can't work without phase alignment. So my question is :
when could we get this feature in UHD ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
This feature is currently supported in the master branch. I will update
the document when it is moved to release. If you search the list
archives, you can find some information on how to use this feature.
Here's a quote from one such e-mail sent by Josh Blum:
"Use set_command_time and clear_command_time around any call you wish to
schedule.
http://files.ettus.com/uhd_docs/doxygen/html/classuhd_1_1usrp_1_1multi__usrp.html#a191b78b00d051d3d51c2f719361c1fb5
Note that this will remove the tune-to-tune offset variations. But you
will probably still need to perform some level of calibration and expect
this to change a bit with temperature, etc. I'd recommend reading the
mimo and sync app note on the kb as well.
-John
On 06/21/2012 07:27 AM, Christophe ALEXANDRE wrote:
Hi all,
i want to use 2 x (N210 + SBX) for a laser telemetry application.
i need to synchronize clocks, align sample times and also have precise
knowledge
of LO phase difference between both N210s.
At the moment, using a mimo cable, i use the following
method : i generate a 1.00005 GHz and inject it on both N210s
with a center frequency equal to 1 GHz.
I get 2 exact 50 kHz complex signals with a constant phase difference.
Each time
i start a measure, i get an other phase difference, still constant.
if i change the frequency from 1 GHz to 1.1 GHz then go back
to 1 GHz, the phase difference has changed.
I can't use this for a telemetry application.
i have read this application note :
http://www.ettus.com/content/files/kb/Selecting_an_RF_Daughterboard.pdf
and find this :
_Do I plan to implement beamforming or direction finding (DF)
capability? _
While all daughterboards can be used in a MIMO configuration, this
does not necessarily imply there is phase alignment between the RF
chains of one or more daughterboards. The BasicRx, BasicTX, LFRX and
LFTX are exceptions to this, since they do not include local
oscillators that contribute to phase ambiguity between channels.
The Ettus Research SBX daughterboard utilizes an RF PLL that includes
a resynchronization feature, which can be used to align the LOs across
multiple SBXs, and multiple USRP hardware devices. Using the
UHD (USRP Hardware Driver^(TM)), timed SPI commands can drive this
re-synchronization feature. At the time of this writing, this feature
is not supported in the mainline UHD. However, this feature is planned
for release in 2012.
I can't work without phase alignment. So my question is :
when could we get this feature in UHD ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
mailto:christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
hi John,
i have already read this app note (in fact, i have started with it).
I've only seen a star after phase on table 2 for SBX but no more info.
what is the basic principle used to solve the phase alignment problem ?
can i use this new feature using gnuradio ?
do you have any example (even C++ example) showing how to use it ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
----- Original Message -----
From: John Malsbury
To: usrp-users@lists.ettus.com
Sent: Thursday, June 21, 2012 4:33 PM
Subject: Re: [USRP-users] LO phase alignment
This feature is currently supported in the master branch. I will update the document when it is moved to release. If you search the list archives, you can find some information on how to use this feature. Here's a quote from one such e-mail sent by Josh Blum:
"Use set_command_time and clear_command_time around any call you wish to
schedule.
http://files.ettus.com/uhd_docs/doxygen/html/classuhd_1_1usrp_1_1multi__usrp.html#a191b78b00d051d3d51c2f719361c1fb5
Note that this will remove the tune-to-tune offset variations. But you will probably still need to perform some level of calibration and expect this to change a bit with temperature, etc. I'd recommend reading the mimo and sync app note on the kb as well.
-John
On 06/21/2012 07:27 AM, Christophe ALEXANDRE wrote:
Hi all,
i want to use 2 x (N210 + SBX) for a laser telemetry application.
i need to synchronize clocks, align sample times and also have precise knowledge
of LO phase difference between both N210s.
At the moment, using a mimo cable, i use the following
method : i generate a 1.00005 GHz and inject it on both N210s
with a center frequency equal to 1 GHz.
I get 2 exact 50 kHz complex signals with a constant phase difference. Each time
i start a measure, i get an other phase difference, still constant.
if i change the frequency from 1 GHz to 1.1 GHz then go back
to 1 GHz, the phase difference has changed.
I can't use this for a telemetry application.
i have read this application note :
http://www.ettus.com/content/files/kb/Selecting_an_RF_Daughterboard.pdf
and find this :
Do I plan to implement beamforming or direction finding (DF) capability?
While all daughterboards can be used in a MIMO configuration, this does not necessarily imply there is phase alignment between the RF chains of one or more daughterboards. The BasicRx, BasicTX, LFRX and LFTX are exceptions to this, since they do not include local oscillators that contribute to phase ambiguity between channels.
The Ettus Research SBX daughterboard utilizes an RF PLL that includes a resynchronization feature, which can be used to align the LOs across multiple SBXs, and multiple USRP hardware devices. Using the
UHD (USRP Hardware DriverT), timed SPI commands can drive this re-synchronization feature. At the time of this writing, this feature is not supported in the mainline UHD. However, this feature is planned for release in 2012.
I can't work without phase alignment. So my question is :
when could we get this feature in UHD ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
On 06/21/2012 08:48 AM, Christophe ALEXANDRE wrote:
hi John,
i have already read this app note (in fact, i have started with it).
I've only seen a star after phase on table 2 for SBX but no more info.
what is the basic principle used to solve the phase alignment problem ?
Does this example help:
http://files.ettus.com/uhd_docs/manual/html/sync.html#align-los-in-the-front-end-sbx-wbx-n-series
can i use this new feature using gnuradio ?
Yes
do you have any example (even C++ example) showing how to use it ?
Link above.
-josh
Hi Josh,
i've read the link :
Using timed commands, multiple frontends can be tuned at a specific time.
This timed-tuning ensures that the phase offsets between VCO/PLL chains will
remain constant after each re-tune. See notes below:
a.. There is a random phase offset between any two frontends
b.. This phase offset is different for different LO frequencies
c.. This phase offset remains constant after retuning
a.. Due to divider, WBX phase offset will be randomly +/- 180 deg after
re-tune
d.. This phase offset will drift over time due to thermal and other
characteristics
e.. Periodic calibration will be necessary for phase-coherent applications
I still don't understand the principle you use. is it a VCO special property
?
some questions still remain :
Q1) if i change LO freq from f1 to f2 then back to f1, should i get the same
phase offset on f1 ?
Q2) if i turn off the N210s then on, should i get the same offset on the
same freq ?
Q3) if the Q1, Q2 answers are yes, what kind of phase offset precision
should i expect ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
----- Original Message -----
From: "Josh Blum" josh@ettus.com
To: usrp-users@lists.ettus.com
Sent: Thursday, June 21, 2012 5:53 PM
Subject: Re: [USRP-users] LO phase alignment
On 06/21/2012 08:48 AM, Christophe ALEXANDRE wrote:
hi John,
i have already read this app note (in fact, i have started with it).
I've only seen a star after phase on table 2 for SBX but no more info.
what is the basic principle used to solve the phase alignment problem ?
Does this example help:
http://files.ettus.com/uhd_docs/manual/html/sync.html#align-los-in-the-front-end-sbx-wbx-n-series
can i use this new feature using gnuradio ?
Yes
do you have any example (even C++ example) showing how to use it ?
Link above.
-josh
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
On 06/22/2012 01:58 AM, Christophe ALEXANDRE wrote:
Hi Josh,
i've read the link :
Using timed commands, multiple frontends can be tuned at a specific
time. This timed-tuning ensures that the phase offsets between VCO/PLL
chains will remain constant after each re-tune. See notes below:
a.. There is a random phase offset between any two frontends
b.. This phase offset is different for different LO frequencies
c.. This phase offset remains constant after retuning
a.. Due to divider, WBX phase offset will be randomly +/- 180 deg
after re-tune
d.. This phase offset will drift over time due to thermal and other
characteristics
e.. Periodic calibration will be necessary for phase-coherent applications
I still don't understand the principle you use. is it a VCO special
property ?
Its a simple principal. When you tune the SBX, the last thing that
happens is that the accumulators reset to zero.
So if you time the event of tuning across multiple devices, the
accumulators will all reset at the same time. Ergo, the phases of the
LOs march in lock step.
some questions still remain :
Q1) if i change LO freq from f1 to f2 then back to f1, should i get the
same phase offset on f1 ?
Q2) if i turn off the N210s then on, should i get the same offset on the
same freq ?
Q3) if the Q1, Q2 answers are yes, what kind of phase offset precision
should i expect ?
Essentially no. There is no absolute phase reference to come back to. A
group of LOs simply become phase aligned upon tuning.
-josh
so the only solution is to share
the same LO across multiple SBX ?
is there any "simple" way to do this ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
----- Original Message -----
From: "Josh Blum" josh@ettus.com
To: "Christophe ALEXANDRE" christophe.alexandre@cnam.fr
Cc: usrp-users@lists.ettus.com
Sent: Friday, June 22, 2012 6:13 PM
Subject: Re: [USRP-users] LO phase alignment
On 06/22/2012 01:58 AM, Christophe ALEXANDRE wrote:
Hi Josh,
i've read the link :
Using timed commands, multiple frontends can be tuned at a specific
time. This timed-tuning ensures that the phase offsets between VCO/PLL
chains will remain constant after each re-tune. See notes below:
a.. There is a random phase offset between any two frontends
b.. This phase offset is different for different LO frequencies
c.. This phase offset remains constant after retuning
a.. Due to divider, WBX phase offset will be randomly +/- 180 deg
after re-tune
d.. This phase offset will drift over time due to thermal and other
characteristics
e.. Periodic calibration will be necessary for phase-coherent
applications
I still don't understand the principle you use. is it a VCO special
property ?
Its a simple principal. When you tune the SBX, the last thing that
happens is that the accumulators reset to zero.
So if you time the event of tuning across multiple devices, the
accumulators will all reset at the same time. Ergo, the phases of the
LOs march in lock step.
some questions still remain :
Q1) if i change LO freq from f1 to f2 then back to f1, should i get the
same phase offset on f1 ?
Q2) if i turn off the N210s then on, should i get the same offset on the
same freq ?
Q3) if the Q1, Q2 answers are yes, what kind of phase offset precision
should i expect ?
Essentially no. There is no absolute phase reference to come back to. A
group of LOs simply become phase aligned upon tuning.
-josh
On 06/22/2012 09:26 AM, Christophe ALEXANDRE wrote:
so the only solution is to share
the same LO across multiple SBX ?
is there any "simple" way to do this ?
Maybe I misunderstood the question and answered incorrectly.
If you tune all N channels at the same time,
they will have the same phase.
-josh
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
----- Original Message ----- From: "Josh Blum" josh@ettus.com
To: "Christophe ALEXANDRE" christophe.alexandre@cnam.fr
Cc: usrp-users@lists.ettus.com
Sent: Friday, June 22, 2012 6:13 PM
Subject: Re: [USRP-users] LO phase alignment
On 06/22/2012 01:58 AM, Christophe ALEXANDRE wrote:
Hi Josh,
i've read the link :
Using timed commands, multiple frontends can be tuned at a specific
time. This timed-tuning ensures that the phase offsets between VCO/PLL
chains will remain constant after each re-tune. See notes below:
a.. There is a random phase offset between any two frontends
b.. This phase offset is different for different LO frequencies
c.. This phase offset remains constant after retuning
a.. Due to divider, WBX phase offset will be randomly +/- 180 deg
after re-tune
d.. This phase offset will drift over time due to thermal and other
characteristics
e.. Periodic calibration will be necessary for phase-coherent
applications
I still don't understand the principle you use. is it a VCO special
property ?
Its a simple principal. When you tune the SBX, the last thing that
happens is that the accumulators reset to zero.
So if you time the event of tuning across multiple devices, the
accumulators will all reset at the same time. Ergo, the phases of the
LOs march in lock step.
some questions still remain :
Q1) if i change LO freq from f1 to f2 then back to f1, should i get the
same phase offset on f1 ?
Q2) if i turn off the N210s then on, should i get the same offset on the
same freq ?
Q3) if the Q1, Q2 answers are yes, what kind of phase offset precision
should i expect ?
Essentially no. There is no absolute phase reference to come back to. A
group of LOs simply become phase aligned upon tuning.
-josh
To clarify here, as long as all LOs are tuned at the same time, you
will always get the same phase offset. If you retune one, you have to
retune the others simultaneously.
Matt
On Fri, Jun 22, 2012 at 1:58 AM, Christophe ALEXANDRE
christophe.alexandre@cnam.fr wrote:
Hi Josh,
i've read the link :
Using timed commands, multiple frontends can be tuned at a specific time.
This timed-tuning ensures that the phase offsets between VCO/PLL chains will
remain constant after each re-tune. See notes below:
a.. There is a random phase offset between any two frontends
b.. This phase offset is different for different LO frequencies
c.. This phase offset remains constant after retuning
a.. Due to divider, WBX phase offset will be randomly +/- 180 deg after
re-tune
d.. This phase offset will drift over time due to thermal and other
characteristics
e.. Periodic calibration will be necessary for phase-coherent applications
I still don't understand the principle you use. is it a VCO special property
?
some questions still remain :
Q1) if i change LO freq from f1 to f2 then back to f1, should i get the same
phase offset on f1 ?
Q2) if i turn off the N210s then on, should i get the same offset on the
same freq ?
Q3) if the Q1, Q2 answers are yes, what kind of phase offset precision
should i expect ?
regards.
Christophe ALEXANDRE
Conservatoire National des Arts et Métiers (CNAM)
Laboratoire CEDRIC-LAETITIA
Département EASY
Accès 17-1-32, Case 2D2P10
292 rue Saint Martin
75141 PARIS CEDEX 03
FRANCE
email : christophe.alexandre@cnam.fr
tel. 0140272699
mob. 0651087311
fax. 0140272994
----- Original Message ----- From: "Josh Blum" josh@ettus.com
To: usrp-users@lists.ettus.com
Sent: Thursday, June 21, 2012 5:53 PM
Subject: Re: [USRP-users] LO phase alignment
On 06/21/2012 08:48 AM, Christophe ALEXANDRE wrote:
hi John,
i have already read this app note (in fact, i have started with it).
I've only seen a star after phase on table 2 for SBX but no more info.
what is the basic principle used to solve the phase alignment problem ?
Does this example help:
http://files.ettus.com/uhd_docs/manual/html/sync.html#align-los-in-the-front-end-sbx-wbx-n-series
can i use this new feature using gnuradio ?
Yes
do you have any example (even C++ example) showing how to use it ?
Link above.
-josh
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com