Re: [Discuss-gnuradio] How can we measure the frequency offsets between two USRPs?

[John Andrews]

I am using GRC. I used a signal source block generating a complex sine at 100kHz. The USRP interpolation is 128 and the sampling rate of the sine generator is 1MHz. The USRP connected to another computer has USRP source configured at 64 decimation and is connected to an FFT block. I don't see any peak at the expected frequency or anywhere in the plot. Its just a flat plot. I checked the USRP settings on both and they are configured right. I even have transmit gain and receive gain as 10dB on both sides.

What can be wrong here?

Thanks

On Mon, May 16, 2011 at 12:09 PM, Marcus D. Leech <address@hidden> wrote:

On 16/05/2011 1:03 PM, John Andrews wrote:

Shouldn't I use some kind of modulation scheme to do this, like FM or AM, to transmit a tone?

No, you can just transmit a narrow, single-frequency tone, and use the receivers FFT to determine how far off it is from
  where you expect it.

use a signal-source producing a SIN wave at, let's say, 1KHz, feed that into a UHD/USRPx sink tuned to whatever your frequency is.
  The tone will appear at TUNED-FREQUENCY+1KHz.

On Mon, May 16, 2011 at 10:02 AM, Marcus D. Leech <address@hidden> wrote:

On 16/05/2011 10:26 AM, Alexander Chemeris wrote:

You may also look into this code:
http://thre.at/kalibrate/
It estimates offset of an USRP with regards to a GSM base station, but
it can be easily modified to measure offset from any clean tone, e.g.
transmitted by a second USRP.

Keep in mind that the offset measured must necessarily be the total offset--that is, both Rx and Tx can be "off" in frequency.

The practical consequence should be NIL, because frequency correction should normally only be done on the Rx-side, and it should
 simply adapt to whatever it sees, regardless of the Tx and Rx components of the offset.


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