Troubleshooting (RFID)

Demodulation fails to lock on signal

Signal not present.

Check connections

Carrier too far from center frequency.

Adjust center frequency. The VSA center frequency must be within carrier lock range to lock properly, see Set the Center Frequency.

Input is over-loaded or under ranged.

Adjust input range. Typically, the best RCE Relative Constellation Error is the RMS level of the Error Vector Magnitude, averaged over all subcarriers and all detected OFDM symbols. (EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format.) is achieved when the range is as small as possible while avoiding overloads.

Frequency span is too narrow.

Increase frequency span.

Wrong bit rate.

Enter the correct bit rate (not the symbol rate).

Wrong modulation format.

Select the correct modulation format (Fwd Format or Ret Format).

Acquisition length too short.

Increase the Acquisition Length.

Signal filtering interfering with auto-detection of bit rate

Ensure the settings on the Filter Tab correspond to the filtering used in the signal.  

Disable Auto Bit Rate/Tari.

Set the ASK Upper threshold to 60% and the ASK Lower threshold to 40%.

Difficulty triggering on start of burst

Triggering holdoff not set.

Trigger holdoff should be used to prevent triggering off of edges within a burst.  The trigger holdoff style should be set to “Above Level”, because an RFID signal is “on” in between bursts.

SYNC NOT FOUND

Incorrect sync word.

Check and correct sync word.  Note that the sync pattern must specify the raw bit pattern to sync to, not the decoded sync pattern.  View the Raw Demod Bits trace to see the raw bits that are found.

Tag's return signal has flipped amplitude phase.

If a tab's signal has a flipped amplitude phase, the standard pattern sync search can fail. The standard pattern search is performed using the raw demodulated bits. If the signal has a flipped amplitude phase, the bits do not match the bit patterns defined by the protocol standard.

BURST NOT FOUND

Acquisition length too short.

Increase Acquisition Length or adjust triggering to ensure that leading and trailing edges of pulse are fully within the Acquisition Length.

Signal length not optimized.

Try the following method to determine Acquisition Length:

AL = (2*MaxOn) + MaxOff

Where:

AL is acquisition length in seconds.

MaxOn is the maximum on time of a burst in seconds.

MaxOff is the maximum off time between bursts in seconds.

Burst Index larger than number of bursts present.

Decrease Burst Index parameter

Spectrum shows DATA?

No bursts found, or Burst Index parameter larger than number of bursts present.

Increase Acquisition Length, or decrease Burst Index parameter.

Pulse found but incorrectly aligned

Poor signal-to noise ratio or on/off ratio.

Check input range setting.

Span is too narrow.

Increase frequency span to prevent degradation of pulse edges.

Error Time shows large error between symbols

Filter mismatch or wrong filter Alpha /BT Bandwidth Time Product.

Adjust measurement filter or filter's Alpha/BT.

Error Time shows regions of large errors

Distortion or a poor signal to-noise ratio causing bit errors.

Check input range.

Errors larger than expected and Error Time shows a uniform distribution of errors

Frequency span too narrow.

Increase Span.

Input is overloaded or under-ranged.

Adjust input range.

Wrong filter selections.

Check that filter selections allow the filtered measured signal to match the reference signal.

Channel conditions have biased symbol timing recovery.

Observe eye diagrams and use the Clock Adjust parameter to compensate symbol timing recovery.

Time corrections disabled.

Enable time corrections.

The trace data constellation symbol location shapes (such as dots) are not properly displayed

The display driver is not functioning correctly.

Contact your PC manufacturer to see if a newer version of the display driver is available. If not, try decreasing the hardware acceleration. See the Windows documentation for instructions.