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

GNU Radio
1

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

2

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

3

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

4

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

5

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