Frequency Response Troubleshooting

This topic offers troubleshooting for the frequency response performance tests and adjustments:

Performance Test Troubleshooting

If the Frequency Response Test fails by a small amount (5 dB or less), the instrument can probably be fixed by performing the Flatness Adjustment. If an adjustment cannot fix the problem, or the test fails by a large error (5 dB or more), this would indicate a faulty assembly.

In order to troubleshoot an RF problem, refer to the analyzer Service Guide for troubleshooting procedures and the overall block diagram. Assemblies can be bypassed by injecting 322.5 MHz or 22.5 MHz signals at the appropriate places.

If the frequency response test fails at frequencies 3.6 GHz and above (high bands), the following should be done: 

  • Perform the Frequency Response Adjustment in its entirety. If the adjustment does not fix the problem, or the adjustment can not complete, suspect a hardware problem. Major assemblies at fault could be: the A12 YTF Assembly; the YTF control signals from the A15 Front End Control Board may be wrong; or the A13 Front End Assembly could be damaged.

If the frequency response test fails at frequencies below 3.6 GHz (Low band), the following should be done:

  • Perform the Frequency Response Adjustment in its entirety. If the adjustment does not fix the problem, or the adjustment cannot complete, suspect a hardware problem. Major assemblies to suspect are: the A13 Front End Assembly, A11 Low Band Switch Assembly, or the A15 Front End Control Board.

If frequency response fails at several frequencies between 9 kHz and the maximum frequency range of the analyzer (failures in both High band and Low band), and a readjustment does not fix the problem, suspect assemblies that are common to both High and Low bands such as a damaged Input Attenuator or the A11 Low Band Switch Assembly.

If the Frequency Response test fails in the Preamp On path, run the Attenuator Slope (Preamp On) Adjustment.

Classic Technique

The Frequency Response tests are performed with classic power sensor/splitter techniques. Mismatch error (though present) is minimized by using good connector care practices. The Frequency Response specification below 3.6 GHz is very small, so any mismatch error could affect the test results. If a millimeter UXA fails the Frequency Response test (even after being adjusted), it could indicate that there is a problem with the test setup, or the UXA input.

Timeout Errors

The EA3 Frequency Response Performance Test will sometimes encounter a GPIB timeout when the test is started. This timeout will occur if Basic Mode (I/Q Analyzer) is not preloaded in the signal analyzer. This situation occurs if large measurement applications (LTE for instance) are preloaded on the instrument instead of Basic Mode. The timeout occurs because the analyzer tries to start Basic Mode, but it must first remove applications from memory in order to load Basic Mode. If the time to clear memory and then load Basic Mode takes too long, then TME will interpret this to be a GPIB timeout. The way to fix this timeout issue is to manually preload Basic Mode in the analyzer.

Adjustment Troubleshooting

Classic Technique

The Frequency Response Adjustment has three distinct steps. Each step can have a unique failure mode.

  1. Collecting the Adaptive Trace

    In this step the DUT is swept at a very slow sweep rate, and the source is swept in a very fast sweep rate. The sweep times are established so there is a high probability that the source will fill a trace bucket with data. Occasionally a bucket will not be filled with data. When this happens a "dropout" will occur in the DUT trace. Dropouts are generally random events. The routine allows for some dropouts to occur. If too many dropouts occur in one trace, then re-running the adjustment will generally fix the issue. If retesting does not fix the issue, then the DUT firmware should be upgraded to greater than version A.04.29.

  2. Performing the Buried Sensor Calibration

    In this step the test system loss is characterized. The calibration process sets the reference sensor power to a specific power and then performs a buried sensor measurement. The two sensor’s amplitude difference is saved as a system correction. The calibration algorithm has limits which the reference sensor power can be within. A failure will occur if the reference sensor power cannot be set within these limits. A failure generally indicates a broken or damaged component in the test system. Basic troubleshooting techniques will identify the suspect component.

  3. Determining the Flatness Correction

    The flatness correction is the DUT conversion loss relative to 50 MHz (or 4800 MHz). An excessive flatness correction can suggest that an internal assembly is not working properly. The adjustment algorithm places limits around the flatness corrections in order to identify instruments that are performing atypically. The Service Guide can help troubleshoot to the suspect assembly.  

PNA-X Technique

The millimeter UXA and PXA (Options 544 and 550) frequency response adjustment uses a PNA-X network analyzer for the signal source. The PNA-X provides a vector corrected input signal to the DUT. In other words, the frequency response corrections are the true amplitude corrections with mismatch error removed from the system.

If there are connectivity problems with the power meter when running the adjustments or utilities that use the network analyzer, ensure the power meter is correctly connected to the PNA-X. Please refer to the power sensor calibration section in the Network Analyzer Freq Sweep Calibration topic.

If the connections have been thoroughly checked and are correct, then there may be a problem with the network analyzer. A system recovery of the network analyzer may be necessary. Please contact network analyzer support for more information and procedures.

Note that the firmware version may change and information will be lost after doing the recovery.