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Discussion and technical support related to USRP, UHD, RFNoC
View all threadsSymbol Synchronous recording
Dear All,
I have USRP 200 and would like to record symbol-synchronous samples at
22MSample per second. I understand that with the internal clock I can sample
at 25MSample per second, but I wonder if using an external clock that is
symbol-synchronous is possible with the board I have.
If this is not possible I would appreciate if you share thoughts of hot to
do this.
I am using SBX 400-4400 MHz Rx/Tx daughterboard.
Best regards,
Zohair
I would suggest recording at 25 MS/s and then converting to 22 MS/s. This
is easy to do with GNU Radio. You could probably even do it in real time,
but if you can't, just record to disk at 25 MS/s and then postprocess the
data.
If you really need the hardware to sample at 22 MS/s, you could replace the
main 100 MHz oscillator with one at 88 MHz (22x4), but that is not a
standard frequency, so it would be a custom part that you would need to get
from the crystal manufacturer. I would recommend against this.
Matt
On Fri, Dec 6, 2013 at 2:10 AM, Zohair ABU SHABAN zohair_ms@hotmail.comwrote:
Dear All,
I have USRP 200 and would like to record symbol-synchronous samples at
22MSample per second. I understand that with the internal clock I can
sample at 25MSample per second, but I wonder if using an external clock
that is symbol-synchronous is possible with the board I have.
If this is not possible I would appreciate if you share thoughts of hot to
do this.
I am using SBX 400-4400 MHz Rx/Tx daughterboard.
Best regards,
Zohair
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
One possibility would be replacing the original oscillator with a
programmable one, so it can be reprogrammed according to the current task.
Did this for my USRP1...
Ralph.
From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com] On Behalf Of
Matt Ettus
Sent: Friday, December 06, 2013 6:44 PM
To: Zohair ABU SHABAN
Cc: USRP
Subject: Re: [USRP-users] Symbol Synchronous recording
I would suggest recording at 25 MS/s and then converting to 22 MS/s. This
is easy to do with GNU Radio. You could probably even do it in real time,
but if you can't, just record to disk at 25 MS/s and then postprocess the
data.
If you really need the hardware to sample at 22 MS/s, you could replace the
main 100 MHz oscillator with one at 88 MHz (22x4), but that is not a
standard frequency, so it would be a custom part that you would need to get
from the crystal manufacturer. I would recommend against this.
Matt
On Fri, Dec 6, 2013 at 2:10 AM, Zohair ABU SHABAN zohair_ms@hotmail.com
wrote:
Dear All,
I have USRP 200 and would like to record symbol-synchronous samples at
22MSample per second. I understand that with the internal clock I can sample
at 25MSample per second, but I wonder if using an external clock that is
symbol-synchronous is possible with the board I have.
If this is not possible I would appreciate if you share thoughts of hot to
do this.
I am using SBX 400-4400 MHz Rx/Tx daughterboard.
Best regards,
Zohair
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
Dear Matt and Ralf,
Thank you for the information you've provided. My question was a two-fold
question and sorry for that not being clear enough.
1- The sampling rate issue which can be solved as I understand by
changing the oscillator of be resampling in software.
2- The second issue is that, assuming the first issue is sorted out;
there would be timing offset that needs to be estimated for a communication
system to function. Is it possible to use REF/PPS somehow to match the
sampling time of the ADC to an external synching clock that is already
synchronized to the symbol time?
Best regards,
Zohair
From: Ralph A. Schmid, dk5ras [mailto:ralph@schmid.xxx]
Sent: 09 December 2013 10:22
To: 'Matt Ettus'; 'Zohair ABU SHABAN'
Cc: 'USRP'
Subject: RE: [USRP-users] Symbol Synchronous recording
One possibility would be replacing the original oscillator with a
programmable one, so it can be reprogrammed according to the current task.
Did this for my USRP1...
Ralph.
From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com] On Behalf Of
Matt Ettus
Sent: Friday, December 06, 2013 6:44 PM
To: Zohair ABU SHABAN
Cc: USRP
Subject: Re: [USRP-users] Symbol Synchronous recording
I would suggest recording at 25 MS/s and then converting to 22 MS/s. This
is easy to do with GNU Radio. You could probably even do it in real time,
but if you can't, just record to disk at 25 MS/s and then postprocess the
data.
If you really need the hardware to sample at 22 MS/s, you could replace the
main 100 MHz oscillator with one at 88 MHz (22x4), but that is not a
standard frequency, so it would be a custom part that you would need to get
from the crystal manufacturer. I would recommend against this.
Matt
On Fri, Dec 6, 2013 at 2:10 AM, Zohair ABU SHABAN zohair_ms@hotmail.com
wrote:
Dear All,
I have USRP 200 and would like to record symbol-synchronous samples at
22MSample per second. I understand that with the internal clock I can sample
at 25MSample per second, but I wonder if using an external clock that is
symbol-synchronous is possible with the board I have.
If this is not possible I would appreciate if you share thoughts of hot to
do this.
I am using SBX 400-4400 MHz Rx/Tx daughterboard.
Best regards,
Zohair
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
Yes, the purpose of the 10 MHz reference and PPS is to provide precise time
information. You can determine down to the exact sample when each sample
occurred. You will still need to do symbol timing recovery in most
systems, however, because the exact over the air delay is not known and
varies over time and with mobility.
Matt
On Mon, Dec 9, 2013 at 6:21 AM, Zohair ABU SHABAN zohair_ms@hotmail.comwrote:
Dear Matt and Ralf,
Thank you for the information you’ve provided. My question was a two-fold
question and sorry for that not being clear enough.
1- The sampling rate issue which can be solved as I understand by
changing the oscillator of be resampling in software.
2- The second issue is that, assuming the first issue is sorted out;
there would be timing offset that needs to be estimated for a communication
system to function. Is it possible to use REF/PPS somehow to match the
sampling time of the ADC to an external synching clock that is already
synchronized to the symbol time?
Best regards,
Zohair
From: Ralph A. Schmid, dk5ras [mailto:ralph@schmid.xxx]
Sent: 09 December 2013 10:22
To: 'Matt Ettus'; 'Zohair ABU SHABAN'
Cc: 'USRP'
Subject: RE: [USRP-users] Symbol Synchronous recording
One possibility would be replacing the original oscillator with a
programmable one, so it can be reprogrammed according to the current task.
Did this for my USRP1...
Ralph.
From: USRP-users [mailto:usrp-users-bounces@lists.ettus.comusrp-users-bounces@lists.ettus.com]
*On Behalf Of *Matt Ettus
Sent: Friday, December 06, 2013 6:44 PM
To: Zohair ABU SHABAN
Cc: USRP
Subject: Re: [USRP-users] Symbol Synchronous recording
I would suggest recording at 25 MS/s and then converting to 22 MS/s. This
is easy to do with GNU Radio. You could probably even do it in real time,
but if you can't, just record to disk at 25 MS/s and then postprocess the
data.
If you really need the hardware to sample at 22 MS/s, you could replace
the main 100 MHz oscillator with one at 88 MHz (22x4), but that is not a
standard frequency, so it would be a custom part that you would need to get
from the crystal manufacturer. I would recommend against this.
Matt
On Fri, Dec 6, 2013 at 2:10 AM, Zohair ABU SHABAN zohair_ms@hotmail.com
wrote:
Dear All,
I have USRP 200 and would like to record symbol-synchronous samples at
22MSample per second. I understand that with the internal clock I can
sample at 25MSample per second, but I wonder if using an external clock
that is symbol-synchronous is possible with the board I have.
If this is not possible I would appreciate if you share thoughts of hot to
do this.
I am using SBX 400-4400 MHz Rx/Tx daughterboard.
Best regards,
Zohair
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com