Re: Newbie question on USRP2, synchronization done by the FPGA?,

Hi,

Thanks for the reply. I guess I am just trying to better understand this
diagram:

I understand what the decimating filters are doing, but I’m a little
unclear about the NCO. Does this component phase and frequency lock for
me, or will I have to code that myself?

thanks,

-Sam

On Wed, Sep 1, 2010 at 8:52 PM, Sam K. [email protected] wrote:

or will I have to code that myself?

thanks,

-Sam

No, there is no freq/phase lock in the USRP/USRP2. We have to do this in
software.

You can reference the dbpsk and dqpsk blocks that we have already
written or
the newer dbpsk2/dqpsk2 blocks that use newer techniques for the phase,
frequency, and timing locks.

Tom

Ok, thanks, One more question… So does that mean we control the NCO
from the software?

I will have a look at those blocks.

thanks,

-Sam

— On Wed, 9/1/10, Tom R. [email protected] wrote:

From: Tom R. [email protected]
Subject: Re: [Discuss-gnuradio] Newbie question on USRP2,
synchronization done by the FPGA?,
To: “Sam K.” [email protected]
Cc: [email protected]
Date: Wednesday, September 1, 2010, 9:03 PM

On Wed, Sep 1, 2010 at 8:52 PM, Sam K. [email protected] wrote:

Hi,

Thanks for the reply. I guess I am just trying to better understand this
diagram:

http://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/073/7319/7319f3.inline.jpg

I understand what the decimating filters are doing, but I’m a little
unclear about the NCO. Does this component phase and frequency lock for
me, or will I have to code that myself?

thanks,

-Sam

No, there is no freq/phase lock in the USRP/USRP2. We have to do this in
software.
You can reference the dbpsk and dqpsk blocks that we have already
written or the newer dbpsk2/dqpsk2 blocks that use newer techniques for
the phase, frequency, and timing locks.

Tom

On Wed, Sep 1, 2010 at 9:15 PM, Sam K. [email protected] wrote:

Ok, thanks, One more question… So does that mean we control the NCO from
the software?

I will have a look at those blocks.

thanks,

-Sam

No, the NCO is free running. We compensate for it in software.

Tom

That’s no different than a straight analog receiver though, where LO
phase is generally not coherent with carrier or modulation phase. So
you use PLL or similar demodulators to recover carrier phase

Amiright?


Principal Investigator
Shirleys Bay Radio
Astronomy Consortium
http://www.sbrac.org

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