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


From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] How can we measure the frequency offsets between two USRPs?
Date: Mon, 16 May 2011 13:09:16 -0400
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.17) Gecko/20110414 Thunderbird/3.1.10

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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