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Why Do the NI PXI-5600 NI-Tuner VIs Have a Span Input?

Primary Software: Driver Software>>NI-Tuner
Primary Software Version: 1.2
Primary Software Fixed Version: N/A
Secondary Software: N/A
Hardware: Modular Instruments>>RF Measurement Devices>>PXI-5600

Problem: There are some VIs in the NI-Tuner API that require a span (bandwidth) input, but the NI PXI-5600 downconverter has a fixed 20 MHz real-time bandwidth.

Solution: The NI 5600 RF downconverter module of the NI PXI-5660/5661 RF vector signal analyzer always downconverts a 20 MHz spectrum band from a desired RF to the IF band of 5–25 MHz. If you request a center frequency of 100 MHz, the frequency span of 90–110 MHz will be downconverted to 5–25 MHz at the output terminal of the NI 5600.

The span input to the NI-Tuner VIs should match the expected capture bandwidth and has two functions:

1. To help set hardware parameters. When the span <= 10 MHz in the hardware, the NI 5600 is configured for the best possible phase noise performance and tunes in 5 MHz increments. When the span > 10 MHz, the NI 5600 has a slightly reduced phase noise performance and tunes in 1 MHz increments.
2. To filter the received data in software. The NI 5600 output data is still 20 MHz wide and is filtered to the requested span in software. 

Refer to the NI-Tuner Help in C:\VXIPNP\WinNT\niTuner\Documentation for more information about the NI-Tuner VIs.

Related Links:
Products and Services: NI PXI-5600

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Report Date: 01/16/2007
Last Updated: 07/03/2007
Document ID: 45FIH2JX

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