Re: ETTUS N210 spurious

[Marcus Müller]

Hi Steve, hi Fabien,

agreed, this might simply insufficient *reconstruction filtering*; note that as Marcus 
Leech said, 70 dB is quite a lot, and I'd be surprised if an analog reconstruction filter 
would be much much better.

Best regards,
Marcus

On 01.02.22 12:12, Steve Hubbard wrote:
> Sorry for the late reply. I am guessing you are seeing aliases of the audio signal. 
> Sampling a 1 kHz signal at 32 kHz produces aliases around multiples of the 32 kHz. In the 
> signal processing chain the sampling rate will be increased in stages until the DAC 
> sampling rate is reached. This process of interpolation involves inserting zero valued 
> samples between the existing samples and then applying a digital low pass filter to 
> attenuate the aliases. The stop band of the filter may be -70 dB so low level spurii 
> remain. -70 dB is low enough for most intents and purposes and probably doesn't need fixing.
>
> Steve
>
> On 19/1/22 1:31 am, Fabien PELLET wrote:
> > Hello,
> >
> > When I put a signal generator that produces a sinwave at 1Khz and that feeds an USRP 
> > Sink with a frequency center at 12MHz for example, I got spurs at +/-32Khz, +/-64KHz and 
> > +/-96KHz at the output of my N210 (used with LFTX and LFRX). Whatever the frequency 
> > center of the USRP and the frequency of the baseband signal, I have to spurs around -70dBc.
> >
> > Any idea on where it could come from ? Hardware EMC problem ? Digital treatment issue ? 
> > How to solve it ?
> >
> > Best regards,
> >
> > Fabien, F4CTZ