Mixer Level Offset (Input Analog Tab)

The Mixer Level Offset control adjusts the mixer level power and ADC Analog-to-Digital Converter range to optimize the measurement based on distortion or signal-to-noise performance for the selected Logical Channel.

Key Points

Mixer Level Offset control trades off distortion performance with signal-to-noise performance.
Increasing Mixer Level Offset increases signal-to-noise (SNR Signal-to-Noise Ratio) and distortion. Decreasing Mixer Level Offset decreases distortion and also decreases SNR.
The Range must be set first, then Mixer Level Offset. Changing Range can change what Mixer Level Offset settings are available.
Mixer Level Offset control is not available for all hardware. The Mixer Level Offset control selection is grayed out if not available.
Mixer Level Offset control is relative. 0 dB represents the best balance between distortion and SNR. Performance specifications for particular hardware apply at a Mixer Level Offset of 0 dB unless stated otherwise.

This parameter can be selected for All channels or individually for each available channel. The available channels are displayed in Logical Channel located at the top of the dialog box. If the selections for individual channels are different, the arrow button () after the Mixer Level Offset text box will be orange. Click the arrow button to view the Mixer Level Offset selection for each available channel.

Additional Information

The Mixer Level Offset control adjusts the Input Attenuation and ADC Range of selected measurement hardware controlled by the 89600 VSA Software.

The default Mixer Level Offset setting is a tradeoff between distortion performance and noise sensitivity, with a bias towards low distortion. Some measurements may require lower noise performance, even if the distortion performance is worse. The Mixer Level Offset control allows you to modify that compromise. You may want to increase the Mixer Level Offset to bias the measurement towards better noise performance, or you may want to decrease the Mixer Level Offset to bias the measurement towards better distortion performance.

If your signal is close to the clipping level of the ADC, decreasing Mixer Level Offset may cause clipping. This is the exception to the rule that decreasing Mixer Level Offset reduces distortion.

The Range setting must always be selected before changing the Mixer Level Offset setting. The Range setting helps determine the Mixer Level Offset settings you can select. When you change the Mixer Level Offset setting, you are changing both the Input Attenuation setting in the RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). path and the ADC Range setting in the analog IF path. The Input Attenuation setting and the ADC Range setting both change by the value you set in Mixer Level Offset. For example, if you select 6 dB in Mixer Level Offset, the Input Attenuation setting will decrease by 6 dB and the ADC Range setting will increase by 6 dB.

If your measurement hardware is not supported with Mixer Level Offset control, the Mixer Level Offset control selection will be grayed out. The Mixer Level Offset control property only works with the PSA Series spectrum analyzers. The PSA Series spectrum analyzers are supported in "Basic Mode" only.

The default Mixer Level Offset setting set by the VSA is represented as "0 dB." Any Mixer Level Offset setting you select is relative to the default Mixer Level Offset setting.

The Mixer Level Offset settings you can choose depends on the measurement hardware being controlled by the VSA, the current range setting, and the default Mixer Level Offset set by the VSA. Typically, the amount of adjustment available is more limited on the lower ranges. There may be no adjustment available on the lowest range.

There is no rule about the best Mixer Level Offset setting. The best Mixer Level Offset setting depends on the measurement hardware, characteristics of the signal, and the specification being tested. For example, increasing the Mixer Level Offset past a certain point may improve the Adjacent Channel Power Ratio at frequencies far removed from the main channel, but may increase the intermodulation distortion which degrades the Adjacent Channel Power Ratio on the inner adjacent channels.