Embedded LO Measurements

The Embedded LO feature allows you to make SMC measurements of mixers that have a FIXED LO inside the DUT.  

Note: This feature is available as Opt S9x084A/B, and must be enabled.

In this topic:

Overview - How the VNA measures the embedded LO

Measurements of these devices are challenging for a couple of reasons:

  1. All Embedded LO measurements require the VNA receivers to be tuned to the correct frequency to measure the mixer output, which is highly dependent on the exact LO frequency.

The nominal frequency of the embedded LO is input into the Mixer Setup dialog. This is used as a starting point for the measurement.

Before each DUT measurement sweep, background sweeps are made to determine the frequency of the embedded LO to a configurable degree of accuracy.

Background sweeps...

To measure a DUT with an Embedded LO:

  1. Create a SMC measurement.

  2. In the mixer setup dialog, enter the nominal frequency of the embedded LO as the LO frequency.

  3. Perform a calibration as usual.

  4. Launch and complete the Embedded LO Mode dialog box (below)

How to Launch the Embedded LO Mode dialog box

Using Hardkey/SoftTab/Softkey

Using a mouse

  1. Press Sweep > Source Control > Embedded LO....

  1. Click Stimulus

  2. Select Sweep

  3. Select Source Control

  4. Select Embedded LO...


Embedded LO dialog box help

The Tuning Settings balance LO measurement speed versus accuracy. You can see that accuracy is becoming compromised when noise starts to appear on the measurement trace.

Scroll up to learn more about the Embedded LO measurement process.

Enable Embedded LO  Check to enable measurement of the Embedded LO.

Tuning Method These settings determine the amount of time spent versus the degree of accuracy to which the LO Frequency is measured.  You can see that accuracy is becoming compromised when noise starts to appear on the measurement trace.

Broadband and Precise Does the entire tuning process for each background sweep. See the Overview for more information.

Precise only  Does NOT perform broadband tuning on each sweep. Use this setting when the embedded LO is stable. The signal (after broadband) must be within ½ the tuning IFBW.  If the signal will always be within ½ the IFBW, broadband tuning is not needed. Most satellite components are within 3 kHz absolute so might not need broadband tuning.

Disable tuning  Only the previously measured LO Frequency Delta is applied to the reference mixer LO and VNA receivers.

Tuning Point  Select, or specify, the data point in the mixer sweep that will be used to find the embedded LO frequency. If a marker is enabled, that data point can be used. For broadband and Precise sweeps, choose a point in the mixer sweep where noise is least likely to be found, such as the point of highest gain. This is generally the center of a sweep or the center of a filter if used.

Tune every  Set the interval at which tuning is performed before a measurement sweep. 'Tune every 3 sweeps' means that every third measurement sweep is preceded by tuning sweeps. If the embedded LO drifts, or if regularly changing DUTs, use 'Tune every 1 sweep'.

Broadband Search - Set the frequency span over which to measure the embedded LO frequency.

IFBW  IF Bandwidth used for Broadband and Precise tuning sweeps. This sets the resolution in the Broadband sweeps and sets the max error (1/2 IFBW) for precise tuning. The larger the IFBW, the faster the sweep, but the signal may not be found.

Max Iterations  The maximum number of Precise sweeps to make. When this number is reached, the final measurement is used.

Tolerance  When two consecutive Precise measurements are made within this value, the final measurement is used. If this is not achieved within the Max Iterations value, then the last measurement is used. This is the best of the 'Tunings settings' to change to improve accuracy.

LO Frequency Delta  The absolute difference between the measured embedded LO frequency and the LO setting that is entered in the Mixer Setup dialog. This value is updated each time the embedded LO frequency is measured.  Entering a value is a way to change the LO frequency on the mixer setup without invalidating the calibration.

Find Now  The VNA finds and measures the actual LO frequency using the current dialog settings. This data is displayed in the Status box.

Status window  Displays textual and graphical representation of the Embedded LO measurement sweeps.

Default  Resets the LO Frequency Delta and Tuning parameters to their default settings.

Graph...  Launches the graphical (spectrum analyzer type) display sweeps of the latest embedded LO measurement.



Embedded LO Diagnostic dialog box help

This dialog appears when Graph is clicked on the Embedded LO dialog.

Presents a graphical (spectrum analyzer type) display of the latest embedded LO measurement.

Click Previous and Next to view available Broadband and Precise sweeps. The LO Frequency is displayed in the Marker annotation.