Thank you Dan! Using the adc snapshot, I saw that with no input the adc was toggling between -1 and 0. This was the cause of the spikes in the spectrum. I also looked at the adc samples with a sine wave as the input and everything looked as expected as you described.
Thanks, David On Tue, Jan 15, 2019 at 11:07 AM Dan Werthimer <[email protected]> wrote: > > hi david, > > when you have no signal going into an adc, it will typically chatter > between two values, around -1, 0 and +1, > and you'll see a lot of RFI and interleave spurs, so the spectrum you sent > around doesn't surprise me, > > but if you put in a sine wave that is much larger than the ADC chatter, > say Vpp ranging from -100 to +100 (out of -128 to +127 for an 8 bit ADC), > then the power spectrum spurs should be very small compared to the sine > wave power > (about a factor of 10,000 in power (100 in voltage)). > > can you use the adcsnap shot to look at the samples coming from your adc, > and see what the relative levels are of the sine wave to the noise? > does the power spectrum agree with what you see in the snapshot? > > best wishes, > > dan > > > > > On Tue, Jan 15, 2019 at 9:59 AM David Marsh <[email protected]> wrote: > >> Hi all, >> >> Sorry if this has already been explained/solved. >> I programmed Tutorial 3 onto a SNAP board and noticed some unexpected >> spikes in the spectrum. I have set up the hardware as explained in the >> python script with a 10 MHz, 8dBm reference going into the SYNTH_OSC SMA >> (3rd SMA from the left). >> >> The attached figure shows the spectrum with no input going into the SNAP >> board. There are large spikes in the spectrum every 50 MHz with the largest >> at 200 MHz. >> >> When I add a signal to the SNAP board, I can see it in the spectrometer >> at the correct frequency >> but the other spikes are still present. >> >> Do you know what is causing these spikes and how they can be removed? Any >> help would be greatly appreciated. >> >> Thanks, >> David >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To post to this group, send email to [email protected]. >> > -- > You received this message because you are subscribed to the Google Groups " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > -- You received this message because you are subscribed to the Google Groups "[email protected]" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected].
