Sampling jitter

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!

BR/
Per

On Wed, Mar 17, 2010 at 8:23 AM, Per Z.
[email protected] wrote:

In the figure
-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!

BR/
Per

This all seems reasonable to me. If you have not recalibrated the
clock in 15 years, then, yes, it is definitely possible that it has
aged.

Tom

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