RE: IQ sample interpretation

Dmitry — Thu, 22 Sep 2022 18:09:15 GMT

Hi,

[quote userid="119801" url="~/f/nordic-q-a/92235/iq-sample-interpretation"]For IQ sampling, are the local in-phase and quadrature signals tuned to 2.44GHz, or 2.44GHz+250KHz?[/quote]

As spec says, "The IQ samples are recorded with respect to the RX carrier frequency", that's 2.44GHz.

[quote userid="119801" url="~/f/nordic-q-a/92235/iq-sample-interpretation"]If the local oscillator is set to the carrier frequency, and is not modulated by 250KHz, then we would expect phase samples at 1us apart to be offset by 90 degrees, is this correct?[/quote]

In theory, yes. In real world, 32M oscillators of RX and TX side have some offset. For example, 40ppm will be multiplied by PLL and translated to ~100kHz offset for carrier frequency, so you can see 150kHz or 350kHz. That's what the reference period is for: you can measure a real frequency of CTE during 8 us then use this value in phase calculations.