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[Discuss-gnuradio] sampling jitter

From: Per Zetterberg
Subject: [Discuss-gnuradio] sampling jitter
Date: Wed, 17 Mar 2010 13:23:15 +0100
User-agent: Internet Messaging Program (IMP) H3 (4.0.5)

Dear All,

I have been experimenting with transmitting a tone between two USRP2s equipped with basic daughterboards. The daughterboards are tuned to 20MHz, and the transmitted signal is generated in base-band as a cisoid with 5MHz frequency. The decimation and interpolation rate is 25MHz in both TX and RX.

In the figure
http://www.s3.kth.se/~perz/usrp/phase_noise1.jpg non of the USRP2s are locked to external reference.
In the figure
http://www.s3.kth.se/~perz/usrp/phase_noise2.jpg the two USRPs are locked to the 10MHz ref output of a marconi2024 generator.
In the figure
http://www.s3.kth.se/~perz/usrp/phase_noise3.jpg the two USRP2 are locked to the 10MHz ref of two _different_ marconi2024.

What I gather from this is that the reference of my marconi2024 is better than that built in the usrp2 (first and third figure). Though, it can be much better (second figure). However, then I would need an extremely clean reference. My marconi2024 is specified to have phase-noise better than -124dB/Hz at 20kHz. The results seem to suggest that's not true. However, the generator is 15 years old. Is it likely that it has aged ?

Any response will be appreciated!


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