NI-579x: Difference Between LO Frequency and Frequency Parameters

Updated May 18, 2018

Reported In

Hardware

  • NI-5791
  • NI-5792
  • NI-5793
  • PXIe-7966
  • PXIe-7975
  • PXIe-7976
  • Controller for FlexRIO

Issue Details

There are two parameters that effects carrier frequency for NI-579x: LO frequency [Hz] and frequency [Hz]. What the difference between this parameters? 

Solution

The main difference is that frequency [Hz] defines signal's center frequency, and LO frequency [Hz] defines actual local oscillator frequency.

Additional Information

This section provide more detaild explanetion. 

Let's inspect Host side implementation for seting both of thos parameters. (Configure Frequency.vi inside of Configure Signal.vi)
  1. LO frequency [Hz] sets up local oscillator frequency. coerced LO frequency [Hz] may differ to requested one deu to hardware limitations. 
  2. frequency [Hz] - coerced LO frequency [Hz] sets frequency shift property to FPGA. 
Note: It's common practice to set LO frequency [Hz] to -1. If you do so, frequency [Hz] will used as a local oscillator frequency. 

Take a look on FPGA side. ( Streaming Xcvr (NI 579x) (FPGA).vi )
frequency shift parameter controls frequency correction in digital processing.

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