Specifies an offset from the center frequency value for the downconverter. Use this attribute to offset the measurement away from the LO leakage or DC Offset of analyzers that use a direct conversion architecture. You must set this attribute to half the bandwidth or span of the measurement + guardband. The guardband is needed to ensure that the LO leakage is not inside the analog or digital filter rolloffs. This value is expressed in Hz.

Syntax

RFMXINSTR_ATTR_DOWNCONVERTER_FREQUENCY_OFFSET

Numeric Value

Data Type

Access

Applies To

53

float64

Read/Write

N/A

Remarks


NI recommends using the RFMXINSTR_ATTR_LO_LEAKAGE_AVOIDANCE_ENABLED attribute instead of the Downconverter Frequency Offset attribute. The LO Leakage Avoidance Enabled attribute automatically configures the Downconverter Frequency Offset attribute to an appropriate offset based on the bandwidth or span of the measurement.
Note

This attribute is not supported on a MIMO session.

You do not need to use a selector string if you want to configure this attribute for all signal instances. Specify the signal name in the selector string if you want to configure or read that signal instance. Refer to the Selector String topic for information about the string syntax.

Default values: For spectrum acquisition types, the RFmx driver automatically calculates the default value to avoid residual LO power. For I/Q acquisition types, the default value is 0 Hz. If the center frequency is set to a non-multiple of RFMXINSTR_ATTR_LO_FREQUENCY_STEP_SIZE attribute, this attribute is set to compensate for the difference.

The following valid values correspond to their respective devices:

Name (value)

Description

PXIe-5646

-100 MHz to +100 MHz

PXIe-5830/5831/5832/5840/5841

-500 MHz to +500 MHz

PXIe-5842

-1 GHz to +1 GHz

Other devices

-42 MHz to +42 MHz

Supported Devices: PXIe-5644/5645/5646, PXIe-5830/5831/5832/5840/5841/5842