Attenuation and Level Control

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The setting of attenuation and scale factors in the EOVSA system is critical for several competing criteria:

  • Keeping components within a safe operating range in order to avoid damage to components
  • Keeping the various amplifier stages in both the frontend module (FEM) and downconverter module (DCM) within a linear operating range
  • Keeping the two polarization channels (H and V) matched and balanced
  • Keeping the optical link within a linear range
  • Keeping the 8-bit digitizer from clipping
  • Keeping the power and power-squared products output by the correlator in a range appropriate to correct spectral kurtosis calculation
  • Keeping the pre-correlation power levels in the appropriate range for 4-bit down-sampling

This memo examines each of these issues in turn, and offers explicit guidelines for attenuation and level control, based on experience with the prototype system. The control system must incorporate these guidelines in a manner that both meets the above criteria and also allows a reasonable scheme for calibration that is as simple and practical as possible.