Extended Calibration
  Overview

The Agilent 89600 Extended Calibration Wizard can enhance the measurement accuracy of selected 89600 systems for wide-span measurements. Using an external source, it measures the frequency response of the system at a particular center frequency and range setting. The analyzer then uses this data to correct the time data, digitally filtering the data to compensate for the measured frequency response (both amplitude and phase).

Extended calibration measures amplitude flatness and phase linearity (not the absolute amplitude or phase) of the measurement system, thus improving the accuracy of relative amplitude or relative group delay measurements across the span. This improves the accuracy of any measurement that depends on the measurement system having flat amplitude and linear phase, such as code domain power, error vector magnitude, channel frequency response, am-to-pm conversion, CCDF, or adjacent channel power.

Extended calibration measures the response at the maximum measurement span. After extended calibration, you can change the measurement span without re-calibrating, but if you change the center frequency or the range, you may need to recalibrate. This depends on the system you are calibrating.

The Extended Calibration Wizard guides you through the steps of connecting the calibration source to the analyzer hardware, choosing a source level, and specifying a file in which to store the data. It then performs calibration measurements, stores the data, restores the 89600 to the state it was in before calibration, and enables the 89600 to include this IF calibration data in the time data correction.

You can create separate data files for different hardware setups. Then when you change your measurement hardware you can recall the calibration data for a previously calibrated setup.

Extended Calibration Wizard uses the External IF calibration feature of the 89600. See the 89600 online help for External IF calibration for more information. You can view the data produced by Extended calibration by recalling it as a trace. (Click File, Recall, Recall Trace and select the calibration data file.)


Supported hardware
Extended Calibration
  Supported hardware

The Extended Calibration Wizard requires an external source under the control of the VsaVector application. You must click Utilities, Hardware, Source and select one of the supported sources. (See the 89600 help text for more information about setting up the 89600 to control a source.) The supported sources are:

•	ESG Vector Signal Generator E4438C (requires option 001 or 002)

•	ESG-D Series Digital RF Signal Generator (requires option UND)

E4433B, E4432B, E4431B or E4430B

•	ESG-DP Series Digital RF Signal Generator (requires option UND)

E4437B, E4436B, E4435B or E4434B

The Extended Calibration Wizard calibrates only the following 89600 hardware configurations:

•	89611 with Agilent PSA option H70

•	89611 with customer-supplied downconverter (tuner)

•	89640 or 89641 with or without external downconverter.


Setting up hardware
Extended Calibration
  Setting up hardware

These are typical hardware setups.

89611A with PSA Option H70

89611A with external downconverter

89640/41A with external downconverter


Setting up the source
Extended Calibration
  Setting up the source

To obtain the greatest accuracy, perform the extended calibration with the source set close to the maximum level for your measurement range. You want to maximize the signal-to-noise ratio for the calibration measurements but avoid distortion. The Extended Calibration Wizard suggests a source level and allows you to change it.

If you are calibrating an 89611 with an Agilent PSA option H70 as a downconverter, or an 89640 or 89641 without a downconverter, the default source level is equal to the analyzer's range.

If you are using an external downconverter, and have properly set up the Utilities, Calibration, External Frequency tab, the default source level is the current source output setting. In this case, it is a good idea before calibrating to set the source level to the maximum specified level for your external downconverter (but not so high a level as would produce significant distortion).

The maximum source level is 10 dBm. Source levels above this do not produce good calibrations because of non-linearities in the source.


Saving Extended Calibration data
Extended Calibration
  Saving Extended Calibration data

The Extended Calibration Wizard asks you to specify a file in which to store the data. If you give the name of a file that already exists, the file will be overwritten with the new data. If External IF Calibration is enabled, the default file name is the one currently in use by External IF calibration ; otherwise, the default file name is “ExtendedIf.cal.” To change the file name click on the […] button next to the file name, navigate to the directory desired, and either choose an existing file or type in a new name.

The 89600 External IF calibration feature uses the file created by the Wizard. After running the Wizard, you may verify this by going to the VsaVector application and clicking Utilities, Calibration, External Amplitude. The IF calibration checkbox is selected, and the file name you specified appears in the IF Calibration File text box.

You can perform Extended Calibration for different hardware settings and store the results under different file names. Then, when you change between hardware setups, you can go to the IF Calibration File dialog to recall the previous calibration file that was created for that setup. Click the IF calibration […] button to choose a file name.


Canceling calibration or correction
Extended Calibration
  Canceling calibration or correction

You can abort calibration before it is finished by clicking Cancel. The analyzer is restored to the state it was in before you ran the Wizard.

After a successful calibration, the Extended Calibration Wizard stores the calibration data in the file you specified and enables External IF calibration. This allows the analyzer to use the calibration data in the file for correcting its time data. The legend “EXT AMP” that appears in the 89600 status bar. You can manually turn External IF calibration on and off by clicking Utilities, Calibration, External Amplitude and then clicking the IF Calibration check box.


Limitations
Extended Calibration
  Limitations

The calibration source must be able to tune to the center frequency at which calibration is to be done. The source should also be able to provide a full-scale signal at the range which you wish to calibrate. The quality of the calibration measurement depends on a good signal-to-noise ratio.

After calibration, the correction is most accurate as long as the center frequency or range is not changed. The correction is made relative to the center frequency. You may change the measurement span and the correction will be adjusted appropriately to fit the span. The correction (or the part based on the External IF calibration data) doesn't change if you change center frequency or range, but the hardware characteristics for which you are correcting may change and to some extent invalidate the correction. Nevertheless, the correction may still give better accuracy than no correction at all. Here are some considerations that affect the validity of calibration data being used for correction:

•	Does the frequency response change significantly with a change of center frequency (for example, due to a pre-selection filter before the first mixer of the tuner)?

•	Does the frequency response exhibit hysteresis (i.e., does it change when you tune away from a chosen center frequency and back again)?

•	Does the frequency response change significantly with a change of range (other than by a constant gain or delay over the span)?

•	 Does the frequency response change over time, and how long has it been since the last calibration?

•	Does the frequency response drift with temperature, and has the temperature changed since calibration?

•	Did you replace any of the hardware with equivalent hardware (which nevertheless may have slightly different characteristics?

You must use the above considerations and knowledge of your required measurement performance to determine how often to calibrate. A quick way to determine the accuracy of the correction is to use the flatness macro included with this software to determine the system flatness. To import the flatness macro, click Utilities, Macros then click Recall. Navigate to the directory in which your VSA software is installed (usually C:\Program Files\Agilent\89600 VSA\) and then to Examples\Macros. Choose flatness.vbs. You can run the macro from the Macros dialog, or from the Macros toolbar (Right-click in the toolbar area and check Macros.)


89611 with PSA option H70
Extended Calibration - System Specific Considerations
  89611 with PSA option H70

Extended Cal above 3GHz

For the 89611 system using an Agilent PSA as a downconverter, extended calibration is of great benefit when making measurements above 3 GHz. In this range the PSA employs a YIG-tuned pre-selection filter whose characteristics change with center frequency and with tuning history. For this reason, to achieve the best accuracy you should perform the Extended Calibration each time you change to a new center frequency above 3 GHz. Hysteresis effects may be mitigated by always tuning to either 3 GHz or 26.5 GHz (whichever is farther away) before tuning to your desired center frequency. This may allow you to reuse calibration data taken previously at that center frequency, but the accuracy will be poorer than if you always recalibrate after a center frequency change.

Extended Cal below 3GHz

For frequencies below 3 GHz, the frequency response at a particular center frequency is repeatable. You can calibrate once at a center frequency, store the results in a uniquely named file, and reuse that file for External IF correction whenever you return to that center frequency.

Source Output Power

For all frequencies it is recommended that you do not calibrate on a range above 10 dBm. Source levels above 10 dBm do not produce good calibrations because of non-linearity in the source. Generally, calibration at 0 dBm will apply on any range between -20 and +30 dBm. For ranges below -20 dBm, it is recommended that you re-calibrate any time you change ranges.

See Also

Extended Cal with a user-supplied downconverter

Extended Cal using the 89640/89641 VSA


89611 with user-supplied downconverter
Extended Calibration - System Specific Considerations
  89611 with user-supplied downconverter

When you are using the 89611 with an external downconverter, you must correctly set up the parameters on the External Frequency tab of the Calibration dialog before performing an Extended Calibration. Note especially that the Intermediate Frequency setting is the frequency at which a sine wave signal would appear at the output of the downconverter if a sine wave were input at the External Center Frequency. The calibration will fail if these parameters are not accurately set. For the 89611, the IF must be close to (ideally equal to) 70 MHz.

Ranging is also very important for a good calibration measurement. You must find out the expected full-scale input for your down-converter and the expected output at the IF for a full-scale input. You must adjust the range of the 89611 so that the full-scale output from the downconverter does not overload the 89611, but not so high that the noise begins to dominate your measurements.

Set the calibration source close to full scale for your converter. Note that the signal level is limited to below 10 dBm for the ESG regardless of what you enter into the Wizard. Source levels above 10 dBm do not produce good calibrations.

Please refer to the Limitations section above to determine how often and where you should calibrate your system.


89640/89641
Extended Calibration - System Specific Considerations
  89640/89641 RF Vector Signal Analyzer

If you are not using an external downconverter, single cal provides fully specified accuracy, but extended calibration can enhance the accuracy at some frequencies beyond what the internal calibration can do.

When you use an external downconverter, the extended calibration can compensate for the downconverter's response. The same considerations apply as for the 89611 with user-supplied downconverter.