hi kris, i suggest you test your instrument with two band limited noise sources connected to the ADC's instead of 50 ohm terminators. if you adjust the noise source's power levels to be similar to that in your observations, you'll be able to more accurately measure cross talk and spectral features. the cross talk is poor between a pair of adc's on the same dual adc chip. the rejection improves if the signals are not on the same chip or adc board. best wishes, dan On 9/21/2010 12:02 PM, Kristian Zarb Adami wrote:
Hello all, I was wondering whether any of you have seen the effect shown in the left hand panel of the attached image. We have terminated two inputs on the 1GSA/s ADC board and run them through an FX-correlator. The left hand panel shows the cross-power spectrum after an integration of 20s. I would expect the noise floor to keep decreasing, but for some reason it doesn't and remains at ~ -110dBm with this structure. When we capture raw-ADC data, perform the same thing floating point we don't see such structures, which indicates that this might be a fixed-point issue. Does anyone have any ideas? cheers, Kris
