Re: [Discuss-gnuradio] Phase measurement with Ettus Research N210

[Stephen Harrison]

Just some quick calculations in python:

exact phase increment for 10 MHz:

>>> (10e6/100e6)*2**32

429496729.6

Closest phase increment:

>>> np.round((10e6/100e6)*2**32)

429496730.0

Resulting frequency:

>>> (np.round(10e6/100e6*2**32)/2**32)*100e6

10000000.009313226

We are out by 9.3mHz!

On Tue, Jun 17, 2014 at 3:36 PM, Sylvain Munaut <address@hidden> wrote:

Hi,

> To start I want to characterize the phase noise of the device, therefore
> I send to both the RX channel and to the frequency reference input the
> same 10 MHz signal. I configured the N210 for 200 kHz sampling and a
> carrier frequency of 10 MHz.

The LFTRX doesn't have a tuner so if you set a carrier freq of 10 MHz
the frequency shift is done by the FPGA via CORDIC and  you'll have
numerical errors in there. You just can't get rid of them.


Cheers,

   Sylvain

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