Re: [Discuss-gnuradio] USRP N210 Clock generation

HI Anusha,

this is the wrong mailing list for this -- for your replies, I think
it's best to join usrp-users@lists.ettus.com [1] and continue this
discussion there; I will crosspost my answer.


On 23.07.2014 18:56, Yarlagadda, Anusha (337G) wrote:
> Hi,
> I am using URSPN210 series, have few questions regarding the clocking schemes for this USRP N210. In the website, its mentioned USRP2 and N200/N210 have fixed 100MHz clock which can't be tuned and do not have option to use external clock.
You *can* use an external clock, but it should be a 10MHz one.
>
> We would like to use a different clock rate (49.2MHz) instead of the fixed 100MHz that is generated from the Reference and system clock generation circuit( I think all these clocks i.e fpga clock, TX/RX clock for the RF boaord ADC/DAC clock are generated by the AD9510 that has on chip PLL core and multi ouput clock distribution function).
I'm afraid that doesn't fit the N210 design. You can't use an arbitrary
clock rate -- the idea is to decimate your signal to a integer fraction
of the master clock rate, and transport the signal at that sampling rate
to the host pc for further processing, e.g. resampling.

Furthermore, I'm a little curious what kind of system would preferably
have a sampling rate of $49.2MHz/n, n \in [2,3,4,...]$ -- please be
aware that you can't fit 49.2 MS/s of 16bit I+Q data through 1 Gigabit
of ethernet!
> An external oscillator (U27 or external reference clock) is phase locked to a reference input reference frequency clock of the AD9510.
> In the USRP N210 FPGA Code can we program the divider values of AD9510 over the SPI interface so that the output clock are not fixed?
As being said, the N210 design doesn't really leave much room for this.
>
> We would like to be compatible with our internal Radio waveform rates and frequencies.
In this case, I recommend using a rational resampler on your host. GNU
Radio comes with some -- you can try if you can match your desired
sampling rate with that.

With best regards,
Marcus Müller

[1] http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

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