NIRFSA_ATTR_FFT_WIDTH

NIRFSA_ATTR_FFT_WIDTH

Specific Attribute

Description

Specifies the FFT width of the device. The FFT width is the effective bandwidth of the signal path during each signal acquisition.

Note  The maximum FFT width when using the PXIe-5622 is constrained to 50 MHz or 25 MHz, depending on the digitizer option you purchased. The maximum FFT width when using thing PXIe-5624 is constrained to 400 MHz or 765 MHz, depending on the digitizer configuration.

Note  You can use the NIRFSA_ATTR_FFT_WIDTH attribute with in-band retuning. For more information about in-band retuning, refer to the NIRFSA_ATTR_DOWNCONVERTER_CENTER_FREQUENCY attribute.

NI-RFSA treats the device instantaneous bandwidth as the effective real-time bandwidth of the signal path. The span specifies the frequency range of the computed spectrum. An RF vector signal analyzer can acquire a bandwidth only within the device instantaneous bandwidth frequency. If the span you choose is greater than the device instantaneous bandwidth, NI-RFSA obtains multiple acquisitions and combines them into a single spectrum. By specifying the FFT width, you can control the specific bandwidth obtained in each signal acquisition. If you read the NIRFSA_ATTR_FFT_WIDTH attribute without setting it, NI-RFSA returns the value of the NIRFSA_ATTR_DEVICE_INSTANTANEOUS_BANDWIDTH attribute.

Valid Values:

The lower limit for all FFT width supported devices using the PXIe-5622 IF digitizer is 7.325 kHz. The lower limit for all FFT width supported devices using the PXIe-5624 IF digitizer is 400 MHz or 800 MHz, depending on the FPGA image that is downloaded upon opening the session to the PXIe-5624 IF digitizer.

PXIe-5663/5663E—The FFT width upper limit for the PXIe-5663/5663E depends on the downconverter center frequency and on the module revision of the PXIe-5601 as illustrated in the following table. Refer to the Identifying Module Revision topic for more information about determining which revision of the PXIe-5601 RF downconverter you have installed.

PXIe-5665/5667/5668—The upper limit of the FFT width is the maximum device instantaneous bandwidth.

Note  If you do not set the NIRFSA_ATTR_DEVICE_INSTANTANEOUS_BANDWIDTH attribute, NI-RFSA determines the appropriate IF filter to use based on the value that you set for the FFT width and your specific device. Refer to the following tables to determine which IF filter corresponds to each FFT width frequency range for your device. If you set the NIRFSA_ATTR_DEVICE_INSTANTANEOUS_BANDWIDTH attribute, NI-RFSA selects the appropriate IF filter based on the NIRFSA_ATTR_DEVICE_INSTANTANEOUS_BANDWIDTH attribute and the NIRFSA_ATTR_FFT_WIDTH attribute determines how much bandwidth of that filter is used during acquisition. Refer to the NIRFSA_ATTR_DEVICE_INSTANTANEOUS_BANDWIDTH attribute to determine which IF filter corresponds to the NIRFSA_ATTR_DEVICE_INSTANTANEOUS_BANDWIDTH attribute setting. Device NIRFSA_ATTR_FFT_WIDTH Attribute Value Frequency Range IF Filter PXIe-5603/5665 (3.6 GHz) ≤300 kHz 300 kHz IF filter >300 kHz and ≤5 MHz Through IF filter >5 MHz Through IF filter PXIe-5605/5665 (14 GHz) ≤300 kHz 300 kHz IF filter >300 kHz and ≤5 MHz 5 MHz IF filter >5 MHz Through IF filter PXIe-5667 ≤30 kHz (NIRFSA_ATTR_IF_CONDITIONING_DOWN_CONVERSION_ENABLED attribute set to NIRFSA_VAL_ENABLED) 30 kHz >30 kHz and ≤400 kHz 400 kHz >400 kHz and ≤1.4 MHz 1.4 MHz >1.4 MHz and ≤5 MHz 5 MHz >5 MHz and ≤20 MHz 20 MHz >20 MHz (NIRFSA_ATTR_SIGNAL_CONDITIONING_ENABLED attribute set to NIRFSA_VAL_SIGNAL_CONDITIONING_BYPASSED) Bypass PXIe-5668 ≤300 kHz 300 kHz >300 kHz and ≤5 MHz 5 MHz >5 MHz and ≤100 MHz 100 MHz >100 MHz and ≤320 MHz 320 MHz >320 MHz and ≤400 MHz (high band) 765 MHz (low band) 320 MHz

Note  At frequencies greater than 3.6 GHz, the PXIe-5605 provides a typical bandwidth of 47 MHz at –6 dB with the preselector enabled. The NIRFSA_ATTR_FFT_WIDTH attribute can override the typical bandwidth of the PXIe-5605 up to 57 MHz using an external digitizer and up to 50 MHz or 25 MHz depending on the PXIe-5622 digitizer option you purchased. The increase in bandwidth results in faster signal acquisitions, but amplitude accuracy is decreased for spectrum acquisitions, and magnitude and phase accuracy is decreased for I/Q acquisitions. National Instruments does not guarantee device specifications if you set the NIRFSA_ATTR_FFT_WIDTH attribute greater than the warranted instantaneous bandwidth specification.

Note  When using the PXIe-5606, the 765 MHz IF filter is only available at center frequencies of 3.6 GHz and above.

Default Value: N/A

Supported Devices: PXIe-5663/5663E/5665/5667/5668