On 30/10/2023 20:25, Bill Dower wrote:
Hello,
What does Ettus recommend for the frequency spacing for the IQ cals
and how does the SDR apply the calibrations to the SDR?
They're applied to the DUC/DDC machinery in the FPGA, based on your
tuned frequency.
Do you recommend a calibration spacing of Nyquist so twice the
bandwidth for the frequency spacing?
I think that would depend on the hardware in question. I/Q corrections
are designed to compensate for slightly-imperfect
phase and amplitude balance in complex-baseband mixers. Different
hardware families use different mixers, with different
degrees of phase/amplitude imbalance depending on what they're being
asked to do.
Then how does the SDR apply the IQ cal? For instance if I chirp
across a bandwidth does the SDR pick and IQ cal near the center of the
band or interpolate between two calibration frequencies?
IF you're chirping in baseband, it will be applying corrections based
purely on your tuned frequency. Any time you tune, it
interpolates the corrections based on the I/Q corrections table. But
if you have a swept baseband, it has no idea that is
going on. For broad-band mixers, corrections usually don't have to
be super-fine-grained.
Thank you for your help,
Bill
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