Spurious frequency of about 70 kHz in a KC705 board?
I am working with a KC705 board to drive (by the FMC connector) some RF switchs in a radar system . The radar data are acquired by a PC. We saw an undesired spurious frequency at about 70 kHz after the data processing.
This spurious is about -100 dB under the maximum value of the signal, so we can not see it by using an oscilloscope.
Is it possible that there is a coupling with a regulator having a switching frequency or a control loop of about 70 kHz?
Re: Spurious frequency of about 70 kHz in a KC705 board?
A couple thoughts on your question:
1) What part is the voltage regulator? I looked at the kc705 web page here on Xilinx but I couldn't find a parts list. If its a switching regulator (or regulators) it may spec a spurious free dynamic range.
2) You mention 100 dB below the maximum value of the signal, but its hard to tell what that means. What is the dBm? Or what is the full scale of the signal you're looking at? I'm assuming you mean full scale since you acquire the data on a PC (ADC based).
3) What is the noise floor of your scope?
4) What kind of signals are you sending to the RF switches from the kc705? Control for the switches? Or the signal you want to be switched? Is the Si570 used?