hi tim,
i suggest you phase lock your 20 MHz generator
to the frequency synthesizer that's generating the adc clock,
and setting the input frequency to the exact center of a spectral bin.
(that insures that every spectra will have the same exact and integer
number of sine waves in it).
for example, if you are sampling at 1 Gsps, and you have 1024
spectral bins over a 500 MHz band, then each spectral bin is
488,281 Hz wide, so you should set your input frequency to
19.53125 MHz, which will be the center of bin 40.
best wishes,
dan
On Tue, Jun 4, 2013 at 3:43 PM, Timothy L. Madden mad...@umail.ucsb.eduwrote:
Hi All,
I am working with the Phil Lubin's Deepspace group at UCSB on a ROACH
based spectrometer. I have been testing tutorial 3 using a 1 Volt
peak to peak sine wave with a frequency of 20 MHz. When set the gain
to a reasonable level it outputs a sharp peak in a consistent
location, but the amplitude of the peak changes quite a bit (on the
order of 10%) between accumulations. I just wanted to know if this
was normal, as it makes calibration irritating to say the least. I am
using a revision A ADC2x1000-8.
Thank you for your time,
Luke Madden
