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Measurement Procedure

Hardware version

CANBench Duo v1.2 — Schematic-stage refresh of the V1.1 fabricated prototype. V1.2 is electrically identical to V1.1 and carries the InvenTree-canonical component metadata; no V1.2 boards exist yet — testing and bring-up reference the V1.1 hardware.

Other versions: v1.1 — fabricated prototype (current)

Standard sweep workflow for characterising a DUT's conducted-emissions signature on the LISN-stabilised supply rails. Assumes the bench is set up per Quick Start and the analyser is configured per Spectrum-Analyser Setup.

1. Validate the analyser noise floor​

Terminate the analyser input directly with 50 Ω (no LISN connected). Sweep the band.

Typical observed noise floor on a tinySA ULTRA:

AttenuationNoise floor
20 dB~ −75 dBm
10 dB~ −85 dBm
0 dBbelow ~ −90 dBm

These values are normal and serve as your reference floor for the session. If your analyser shows substantially higher floor, suspect a defective cable, a contaminated terminator, or local RF interference — fix the floor before proceeding.

2. Baseline measurement (LISN powered, DUT disconnected)​

Connect:

  • analyser → LISN+ (J2)
  • 50 Ω terminator → LISN− (J4)
  • 50 Ω terminator → CAN CM (J6)

Apply bench-supply power. Leave the DUT disconnected.

Expected: noise floor approximately equal to the analyser baseline; no significant peaks. Any large peaks here come from the bench supply or the environment, not the DUT. Note them as the environmental baseline — they will appear in every subsequent sweep regardless of the DUT.

3. DUT measurement​

Connect the DUT to the DUT-side banana pair (or via the M12). Power on. Sweep.

Compare against the baseline — only DUT-dependent changes count as conducted-emissions signatures. The interpretation step (which signatures are CM vs DM, which are dominant, what they tell you about the DUT) is covered in Interpreting Results.

4. Additional — CAN common-mode tap (J6, RF_CAN_CM)​

The CAN CM port (J6) taps the CAN bus's common-mode voltage directly, via 1 kΩ matched-pair summing resistors (R38, R41) presenting 2 kΩ series differential load across the bus. Use this when the DUT has CAN connectivity and you want to characterise CAN-bus CM noise independently of the supply-rail measurement.

The CAN CM port does not terminate the bus

J6 is a high-impedance measurement tap. The standard 120 Ω CAN-bus termination must be provided by the DUT or the backbone. Connecting the CAN CM port to an unterminated bus will degrade signalling and produce bus errors.

Workflow:

  • analyser → CAN CM (J6)
  • 50 Ω terminator → LISN+ (J2)
  • 50 Ω terminator → LISN− (J4)
  • Ensure the DUT is connected via the M12 (J10) so the CAN-H / CAN-L pair is energised; or hand-wire the DUT's CAN bus to a backbone that includes the CANBench Duo's J10 in series.

Sweep. The result is the CAN-bus common-mode signature, which often dominates the upper-band emissions of a CAN-bus system and can be analysed independently of the supply-rail CM/DM measurement.

See Interpreting Results for the LISN+/LISN− symmetry comparison and the CANBench TrueZ CM/DM separation workflow.