How can the sampling rate of 5622 be lower than the IF frequency

[BSharmi]

Hi,

the sampling rate of PXIe-5622 is 150 MS/sec but the intermediate frequency for 2.4 GHz range is 187.5 MHz. I am confused how can the IF be higher than the sampling rate of 5622. Shouldn't the sampling rate be 2*187.5 MHz?

Can anyone please explain?

Thanks!

[Tunde_S]

Hi BSharmi,

With the NI PXIe-5622, we are able to reconstruct a spectrum for a 50 MHz bandwidth signal that is centered at 187.5 MHz through the undersampling technique (or bandpass sampling), when the ADC sampling frequency (Fs) is 150 MHz. The white paper article that I linked below, discusses the undersampling technique.

Aliasing and Sampling at Frequencies Above the Nyquist Frequency

http://www.ni.com/white-paper/3000/en/

Also, starting on page 31 of the Super-Heterodyne Signal Analyzer PDF, which is part of the RF Academy Measurement Fundamentals application notes, we provide more information on IF sampling. In this document, it mentions that signals in Nyquist Zone 3 (frequencies between Fs and 1.5*Fs) appear in baseband (or Nyquist Zone 1), as well. By using an anti-alias filter before the ADC, we know that the alias in baseband is for the IF signal.

As a result, the NI RF Vector Signal Analyzers Help documentation mentions that for an IF signal of 187.5 MHz, the NI 5622 operates in the third band (or Nyquist Zone 3).

Digitizer Alias Response

http://zone.ni.com/reference/en-XX/help/372058L-01/nirfsa/digitizer_alias_response/

Regards,

[BSharmi]

Thank you vey much for the reply!