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
