Finding the IF Center Frequency when Using the NI 5600/5601 in Downconverter Only ModeHardware: Modular Instruments>>RF Measurement Devices>>PXI-5600, Modular Instruments>>RF Measurement Devices>>PXI-5660, Modular Instruments>>RF Measurement Devices>>PXI-5661, Modular Instruments>>RF Measurement Devices>>PXIe-5601, Modular Instruments>>RF Measurement Devices>>PXIe-5663
Problem: Downconverter only mode for the NI 5600/5601 is a new feature that was introduced in NI-RFSA 2.1. When using the downconverter in this mode, we need to know the downconverted IF frequency. How can I find this IF frequency generated by the NI 5600/5601 downconverter? Solution: The NI 5600 is specified to have an IF frequency range from 5 MHz to 25 MHz. The NI-RFSA driver will select a local oscillator (LO) frequency such that the downconverted signal is approximately centered around 15 MHz. Depending on the center frequency and frequency span of the RF signal, the tuning resolution of the LO will be limited to steps of 1 MHz and 5 MHz, which is the reason why the IF frequency will not always be centered at exactly 15 MHz. However, unlike the NI 5600, the NI 5601 can downconvert the RF signal to an exact IF frequency by using the NI 5652 RF Signal Generator to source any specific LO frequency using direct digital synthesis (DDS). The downconverted IF frequency for the NI 5601 downconverter is set at either 53 MHz or 187.5 MHz depending on the input RF frequency as shown from the following table in the specifications sheet.  RFSA Downconverter Center Frequency Adjustment.vi consists of two session: an NI-SCOPE session and an NI-RFSA session. The Get IF.vi is used as a subVI to obtain the IF frequency from the NI-RFSA session and specify the center frequency for the NI-SCOPE session. A portion of the block diagram for Get IF.vi is shown below.
  Related Links: Product Manual: NI PXI-5660 Specifications (January 2008) Product Manual: NI PXI-5661 Specifications (November 2007) Product Manual: NI PXI-5663 Specifications (July 2008) Product Manual: NI RF Vector SIgnal Analyzers Help (July 2008) KB 4UMDLQJQ: Using the NI 5660/5661/5663 in Downconverter Only Mode Attachments:  RFSA Downcoverter Center Frequency Adjustment.vi Get IF.vi
Report Date: 08/04/2008 Last Updated: 06/05/2009 Document ID: 4O38K05X |
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