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Today's Topics:
1. LO frequency offset (Francois Quitin)
2. Re: LO frequency offset (Nick Foster)
3. Re: LO frequency offset (Francois Quitin)
----------------------------------------------------------------------
Message: 1
Date: Fri, 8 Jun 2012 14:41:32 -0700
From: "Francois Quitin" <[email protected]>
To: <[email protected]>
Subject: [USRP-users] LO frequency offset
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Dear all,
I?m designing a frequency synchronization algorithm on our USRP-N200 with a
WBX daughterboard, and I?ve been observing some strange behavior with it. So
I?ve run the following test:
I use one USRP-N200 to transmit a constant pilot tone, and I use another
USRP-N200 as receiver. I store the received pilot tone to a file, and
post-process this data to extract the LO frequency offset (Center frequency
of 964 MHz, sample rate of 200kHz). In some cases there is no problem (first
picture), the LO frequency offset changes over time, but nothing surprising.
However, sometimes (second picture), the LO frequency offset ?jumps? several
dozen of Hz.
I asked a colleague from another university to run the same test with their
USRPs-N200, and they have observed the same behavior: the LO frequency
offset sometimes ?jumps?. Even stranger, when I use our older USRP-2, I
never observe this behavior.
Has this happened to someone before? Have I broken something on our boards?
Or is there some flaw in the clock distribution on the USRP-N200?
Thanks a lot,
Fran?ois Quitin, Ph.D.
BAEF Post-doctoral research fellow
Electrical & Computer Engineering Dept.
University of California
Santa Barbara, CA 93106-9560
Phone: +1-805-883-8599
Email: [email protected]
Home: www.ece.ucsb.edu/~fquitin
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Message: 2
Date: Fri, 8 Jun 2012 14:46:29 -0700
From: Nick Foster <[email protected]>
To: Francois Quitin <[email protected]>
Cc: [email protected]
Subject: Re: [USRP-users] LO frequency offset
Message-ID:
<calalhjxtvmjrwwpwn9aa5rbveafipamoejbc4bcdghoptj_...@mail.gmail.com>
Content-Type: text/plain; charset="windows-1252"
The behavior is due to the TCXO used in the N200 series. Small TCXOs
typically use digital correction steps; the step size in this particular
TCXO is relatively large. You can avoid the problem by using an external
reference. You can also configure the N210 to select the "external"
reference, but don't connect a reference. In this case, your absolute
frequency error will go up several orders of magnitude (comparable to the
USRP2), but you will not see the "jumps".
--n
On Fri, Jun 8, 2012 at 2:41 PM, Francois Quitin <[email protected]> wrote:
> Dear all, ****
>
> ** **
>
> I?m designing a frequency synchronization algorithm on our USRP-N200 with
> a WBX daughterboard, and I?ve been observing some strange behavior with it.
> So I?ve run the following test: ****
>
> ** **
>
> I use one USRP-N200 to transmit a constant pilot tone, and I use another
> USRP-N200 as receiver. I store the received pilot tone to a file, and
> post-process this data to extract the LO frequency offset (Center
> frequency of 964 MHz, sample rate of 200kHz). In some cases there is no
> problem (first picture), the LO frequency offset changes over time, but
> nothing surprising. However, sometimes (second picture), the LO frequency
> offset ?jumps? several dozen of Hz. ****
>
> ** **
>
> I asked a colleague from another university to run the same test with
> their USRPs-N200, and they have observed the same behavior: the LO
> frequency offset sometimes ?jumps?. Even stranger, when I use our older
> USRP-2, I never observe this behavior. ****
>
> ** **
>
> Has this happened to someone before? Have I broken something on our
> boards? Or is there some flaw in the clock distribution on the USRP-N200?
> ****
>
> ** **
>
> Thanks a lot, ****
>
> ** **
>
> *Fran?ois Quitin, Ph.D.*
>
> * *
>
> BAEF Post-doctoral research fellow****
>
> Electrical & Computer Engineering Dept. ****
>
> University of California****
>
> Santa Barbara, CA 93106-9560****
>
> Phone: +1-805-883-8599****
>
> Email: [email protected]****
>
> Home: www.ece.ucsb.edu/~fquitin ****
>
> ** **
>
> _______________________________________________
> USRP-users mailing list
> [email protected]
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
>
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------------------------------
Message: 3
Date: Fri, 8 Jun 2012 15:20:05 -0700
From: "Francois Quitin" <[email protected]>
To: "'Nick Foster'" <[email protected]>
Cc: [email protected]
Subject: Re: [USRP-users] LO frequency offset
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hi Nick,
Thanks a lot for your answer ! It makes much more sense now. Does it also
work on the USRP N200 to select ?external? reference without connecting a
reference (and not just the N210) ?
Is there another way to bypass the digital correction steps of the TCXO ?
Thanks a lot,
Fran?ois
De : Nick Foster [mailto:[email protected]]
Envoy? : vendredi 8 juin 2012 14:46
? : Francois Quitin
Cc : [email protected]
Objet : Re: [USRP-users] LO frequency offset
The behavior is due to the TCXO used in the N200 series. Small TCXOs
typically use digital correction steps; the step size in this particular
TCXO is relatively large. You can avoid the problem by using an external
reference. You can also configure the N210 to select the "external"
reference, but don't connect a reference. In this case, your absolute
frequency error will go up several orders of magnitude (comparable to the
USRP2), but you will not see the "jumps".
--n
On Fri, Jun 8, 2012 at 2:41 PM, Francois Quitin <[email protected]> wrote:
Dear all,
I?m designing a frequency synchronization algorithm on our USRP-N200 with a
WBX daughterboard, and I?ve been observing some strange behavior with it. So
I?ve run the following test:
I use one USRP-N200 to transmit a constant pilot tone, and I use another
USRP-N200 as receiver. I store the received pilot tone to a file, and
post-process this data to extract the LO frequency offset (Center frequency
of 964 MHz, sample rate of 200kHz). In some cases there is no problem (first
picture), the LO frequency offset changes over time, but nothing surprising.
However, sometimes (second picture), the LO frequency offset ?jumps? several
dozen of Hz.
I asked a colleague from another university to run the same test with their
USRPs-N200, and they have observed the same behavior: the LO frequency
offset sometimes ?jumps?. Even stranger, when I use our older USRP-2, I
never observe this behavior.
Has this happened to someone before? Have I broken something on our boards?
Or is there some flaw in the clock distribution on the USRP-N200?
Thanks a lot,
Fran?ois Quitin, Ph.D.
BAEF Post-doctoral research fellow
Electrical & Computer Engineering Dept.
University of California
Santa Barbara, CA 93106-9560
Phone: +1-805-883-8599 <tel:%2B1-805-883-8599>
Email: [email protected]
Home: www.ece.ucsb.edu/~fquitin
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