Receiver Leveling

Note: The M937xA/P937xA does not support this function.

Receiver Leveling adjusts the source power until the measured receiver power is equal to the Port Power.

In this topic:

Overview

Receiver Leveling uses receiver measurements to adjust the source power level across a frequency or power sweep. Before each measurement sweep, a variable number of background sweeps are performed to repeatedly measure power at the receiver for each stimulus point. Those power measurements are then used to adjust the source power level and achieve greater source power level accuracy.

This is similar to a Source Power Calibration which makes a single sweep to measure source power. The source power correction values are applied for all subsequent measurement sweeps. Because Receiver Leveling is performed for every measurement sweep, it provides more accurate source power levels, but also takes longer to perform each measurement sweep.

Receiver Leveling Process

Leveling sweeps are performed in the background (not visible) before every measurement sweep to measure and apply source correction data.

For each leveling sweep, source power is applied at each data point and measured by the specified receiver. Learn how the initial power level is selected.
The deviation is calculated between the measured power and the port power.
The deviation is applied to the current source power, and the updated source power levels are applied on the following leveling sweep.
This process continues until the receiver power at each data point has achieved the port power within the specified tolerance value, or until the specified number of leveling sweeps (iterations) has been reached.

Features and Limitations

Receiver Leveling can be used with most sweep types, including Segment sweep and Power sweep.
Receiver Leveling is ALWAYS enabled for the controlled source when Phase Control (Opt S93088A) is enabled.
Receiver Leveling is available for standard S-parameter measurements and with FCA, GCA, and IMD applications.
Turn ON Receiver Leveling before or after doing a Calibration. When turned ON before calibrating, it is turned OFF during the calibration, then back ON after calibration.
Power Offset on the Offsets and Limits dialog can be used when there exists an additional attenuator or booster amplifier in the source path. An offset should be set to improve the leveling speed. This power offset is automatically used to set the port power.

Use Receiver Leveling for the following:

Correcting for short term drift when using an external component, such as a booster amplifier. The booster amplifier must be connected to the front-panel jumpers, in front of the reference receiver. See the Block diagram for your VNA, located at the end of every Specifications document.
Extending the accuracy of power leveling at very low powers where the internal detector may be too noisy.
Providing controlled power during Pulsed measurements in an open loop mode.
Controlling the power at the outputs of MM-Wave heads.

How to make Receiver Leveling settings Start the Power and Attenuators dialog box as follows:
Using Hardkey/SoftTab/Softkey	Using a mouse
Press Power > Main > Power and Attenuators.... On the Power and Attenuators dialog, click Receiver Leveling button.	Click Stimulus, Power, then Power and Attenuators. On the Power and Attenuators dialog, click Receiver Leveling button.

Receiver Leveling dialog box help

Learn about Receiver Leveling (scroll up).

Define Controlled Source (Port)

Each source port to be leveled is configured individually. Select a source to be configured for receiver leveling. Choose from: Port 1, Port 2, Port 3, Port 4, or any active external source. Learn more about External Devices.

Leveling Receiver Setup

Receiver Type Receiver type does an initial sort to make it easier to select a receiver. Choose from: VNA Receiver or Ext. Device (PMAR).

Receiver Select a receiver to be used to level the specified source.

For VNA Receiver type, choose from any VNA receiver using standard or receiver notation.

To level power at the source output or DUT input choose the reference receiver for the source port. For example, to level the source power at port 1, then choose "R1". To level power at the DUT output, choose the receiver that is used to measure the DUT output. If the DUT output is connected to port 2, then select "B" or 'b2". Learn about Receiver Notation.

When Phase Control is enabled, the ratioed receivers used in Phase Control are selected and can NOT be changed. However, the Reference Source CAN also be selected for Receiver Leveling.

For Ext Device type, choose a configured PMAR device.

Level when this RF source is turned ON: The Controlled Source is selected automatically and can NOT be changed.

Receiver frequency is determined by: Available ONLY when the selected receiver is a VNA Receiver or power meter. This setting determines which receiver frequencies are measured. Choose from:

Auto - always uses the frequency range that is assigned to the measurement receiver.
FOM Receiver - FOM Receiver frequency range. Learn more about Frequency Offset Mode.
FOM Source - FOM Source frequency range.
DUT Input - Mixer/Converter input frequency range.
DUT Output - Mixer/Converter output frequency range.

Leveling Loop Tolerance The source is considered leveled when each stimulus data point has achieved the power level +/- (plus or minus) this tolerance value.

Leveling Loop Max Iterations If every stimulus data point does NOT achieve the port power after this number of leveling sweeps, the measurement sweep occurs using the correction values obtained from the last leveling sweep. The message: Not settled, noisy trace appears when the Max Iterations is reached. If you see this message, you can increase the Max Iterations, reduce the IFBW, or increase the Tolerance setting.

Note: If the Max Iterations is set to zero, there will be no pre-sweep for the receiver leveling, but the value of the receiver data will be used to correct the next sweep. In this way setting the value to zero provides a post sweep correction and can be useful for correcting slow drift in a system where a booster amplifier or open loop ALC is used, without adding pre-sweeps to the sweep-acquisitions.

Leveling IFBW Available only for VNA receivers. By default, the IFBW for the leveling sweeps is set to 100 kHz. Learn more about IFBW.

Increase this value to make faster, but noisier leveling sweeps.
Decrease this value to maker slower, more repeatable leveling sweeps.
Uncheck the box to use the same IFBW as the measurement sweeps.

Controlled Source Setup

Update source power calibration with leveling data Available only when using an RF Source and VNA receiver.

When checked, the latest correction data is copied to the Source Power Cal correction array. When Leveling Mode is switched back to Internal (on the Power and Attenuators dialog), Source Power Cal is automatically turned ON using this correction data.
When cleared, Source Power Cal is NOT turned ON when Leveling Mode is switched back to Internal.

Enable Source ALC hardware circuit NOT available with External sources.

Checked - Internal ALC leveling and Receiver Leveling (Recommended).
Cleared - NO ALC leveling; Receiver Leveling ONLY. NOT available on N523x models.

Enable Safe Mode while leveling

To protect your DUT, these settings control the extent to which the source power will be changed to achieve the port power as measured at the reference receiver. These settings could be necessary when using external components with a large variation in frequency response (flatness).

When checked:

The Min source output is used as the initial power level for the leveling loop process.
The controlled source is never stepped more than the Max source step size.

When cleared:

The initial power for the leveling loop may be determined by the Min source output, the Max source output, the last setting of the leveling loop, or the target value of the leveling loop. See Initial Power below.
The Max source step size is ignored.

Max source step size When Safe Mode is enabled, the change in source power at each data point from one sweep to the next is limited to this value. For example, assume Safe Mode is enabled, and Max Power Step is set to 1 dB. On the first leveling sweep, the first data point measures 3 dB lower than the port power, then source power for data point 1 will be increased by 1 dB for the next sweep, and likely for the following two sweeps.

Max port output Always limits the maximum power out of the source to this value. The message: Power set to Max Power appears when this limit is reached.

If the maximum port power out of the VNA is reached at any time during the leveling sweeps, the following message appears: Power set to user power limit.

Min port output Always limits the minimum power out of the source to this value. The message: Power set to Min Power appears when this limit is reached. When Safe Mode is enabled, this value is used as the initial power level for the leveling loop process.

Note: The MAX/MIN limit is always used regardless of the safe mode state. In addition, the MAX/MIN limit is for port power and related to power offset. If the power offset is not set correctly, the MAX/MIN limit is not correct and it may impact the leveling. Ensure that the power offset in the channel is the same as power offset during calibration. If the exact power offset is not known, choose a limit for source and then it will not be related to power offset.

Initial Power Selection

For each displayed data point, the leveling algorithm must select an initial power to begin the iteration process. This value is chosen as follows:

Where:

PInit = the initial power for the iteration process.

PFinal = the final power setting from the previous leveled sweep.

PMin = the minimum controlled source output level as specified in the Receiver leveling setup.

PMax = the maximum controlled source output level as specified in the Receiver leveling setup.

PTarget = the target power level for the selected leveling receiver.