[USRP-users] Phase Noise for USRP N200 with LFTX/LFRX

Ian Buckley ianb at ionconcepts.com
Tue Dec 9 10:24:35 EST 2014


Khalid,
The CVHD-950 in N210 is specified as 100MHz nominal. That 100MHz clock is distributed directly to the ADC without any frequency conversions and used to sample in your case, the whole 30MHz bandwidth available from LFTX as complex baseband.
Any further tuning and reduction in bandwidth via decimation and filtering occurs in the digital down conversion DSP where phase noise is not a consideration.
-Ian

On Dec 9, 2014, at 4:53 AM, khalid.el-darymli via USRP-users <usrp-users at lists.ettus.com> wrote:

> Thanks very much for this information. According to the datasheet you mentioned in the link below [1], the supported oscillating frequency by CVHD-950 is 50 MHz to 130 MHz. The PN specs are provided for some center frequencies in this range. 
> 
> However, I am interested in the HF band for which the LFTX/LFRX support center frequencies up to 30 MHz. For requested center frequencies in (DC, 30 MHz], do you digitally down-sample the center frequency of CVHD-950? Is there any description on how exactly you do that? and what effect does this may have on the phase noise of CVHD-950?
> 
> I am working on an ocean-based HF radar. Basically, the system measures the Doppler frequency of ocean waves for different sea states. It is important that I characterize my system to know its limits and capabilities.
> 
> Thanks for your help.
> 
> Best,
> Khalid
> 
> [1] http://www.crystek.com/home/oscillator/vcxodetail.aspx?pn=CVHD-950
> 
> On Mon, Dec 8, 2014 at 7:35 PM, Matt Ettus <matt at ettus.com> wrote:
> 
> With the LFRX and LFTX, there is no mixer, so all phase noise is from the ADC clock.  The oscillator used is a CVHD-950 from Crystek and you can find the phase noise spec for it on their web site.
> 
> Matt
> 
> On Mon, Dec 8, 2014 at 2:11 PM, khalid.el-darymli via USRP-users <usrp-users at lists.ettus.com> wrote:
> Hi,
> 
> According to the specs provided in [1], the RF performance of USRP N200/N201 is characterized for the WBX daughter-board. Particularly, phase noise measurements are given for three offsets from a center frequency of 1.8 GHz. 
> 
> My question is, are there any such measurements for the LFTX/LFRX daughter-board? 
> 
> If not, is there a recommended procedure for doing these measurements?
> Among others, I am particularly concerned with the phase noise and its short-term effect on my Doppler measurements.
> 
> 
> [1] https://www.ettus.com/content/files/07495_Ettus_N200-210_DS_Flyer_HR_1.pdf
> 
> Thanks,
> Khalid
> 
> 
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