DIAGNOSTIC WORKFLOW / 150 MHz HARNESS RADIATION

Build a traceable evidence chain from failure to root cause.

For a narrowband failure near 150 MHz, correlate harmonic sources, connector mode conversion, harness electrical length, and common-mode current. Use A/B experiments to converge on root cause and record corrective-action limits and regression results. L4 Case

CISPR 25 test method ↗Structured case ↗

PHYSICS CHAIN / SOURCE → PATH → MODE → ANTENNA → VICTIM → EVIDENCE

SourceClock / switching harmonics
PathConnector mode conversion, Reference discontinuity
ModeCommon mode, Mode conversion
AntennaHarness at λ/2 resonance
VictimCISPR 25 receiver
EvidenceCommon-mode current, Before/after spectrum

01 / INTERACTIVE SCENE

Change parameters and observe the path.

Change frequency and harness length to observe common-mode current distribution and resonance; switch layers to locate DM/CM conversion.

Harness length l = 1.00 mFrequency f = 150 MHzTermination = 150 Ω

Wavelength λ

200.0 cm

Electrical length l/λ

0.500 λ · CM

Radiation trend

Resonant region (high radiation resistance)

Conceptual model · not a simulation · evidence level L1. Use the trend to build intuition; absolute field strength requires CISPR 25 measurement. Limit: small-loop/far-field approximation; for length > λ/2, multi-lobe behavior invalidates a simple monopole approximation.

Cool blue: Voltage / electric field / capacitive coupling
Amber: Current / magnetic field / inductive coupling
Purple: Mode conversion, such as differential to common mode
Green: Measurement support
Red: Risk or limit exceedance
Neutral white-grey: Geometry, grid and neutral information

02 / PHYSICAL EXPLANATION

Four views of the same phenomenon.

Explain the same phenomenon through intuition, engineering structure, mathematical relationships, and measurement evidence, with limits stated for each view.

Intuitive view

A 1 m cable approaches half-wave resonance near 150 MHz and can become an effective antenna.

Engineering view

Differential-to-common-mode conversion near the connector drives harness common-mode radiation.

Mathematical view

E ∝ I_cm·l·f²; f_corner=1/(π·t_r); S_cd21=b_c/a_d

Measurement view

Measure common-mode current with a current probe; use the CISPR 25 ALSE setup and before/after spectra.

03 / DIAGNOSTIC EXPERIMENTS

Run A/B experiments and let evidence converge the hypothesis.

Progress through hypotheses, discriminating experiments, evidence, and root cause. Do not state a deterministic conclusion without sufficient measurement evidence.

1.INTAKE2.NORMALIZE3.HYPOTHESES4.EXPERIMENTS5.EVIDENCE6.ROOT CAUSE7.REGRESSION

Candidate hypotheses (generated from the physics chain and related cases)

Harness electrical length creates a resonance near 150 MHz.PROPOSED

Unknown conditions: Harness termination impedance; Effect of effective permittivity on wavelength→ e1-vary-length、e2-ferrite-position

Connector-region imbalance converts differential energy into common-mode current.PROPOSED

Unknown conditions: Pin-level connector asymmetry; Mixed-mode S-parameters required for DM/CM decomposition→ e3-nearfield-connector、e4-cmc-at-connector

A board-level high-di/dt loop couples directly into the harness path.PROPOSED

Unknown conditions: Hot-loop area; Coupling path from the hot loop to the harness→ e5-nearfield-hotloop

Discriminating experiments (ranked by discriminating power; run as A/B tests)

Root-cause convergence check

Current evidence is insufficient to converge on a root cause:

No hypothesis is confirmed; more discriminating experiments are required.
No before/after A/B evidence is recorded.
No level L3 measurement evidence or stronger evidence is recorded.

The system organizes hypotheses and evidence; it does not output uncalibrated root-cause probabilities. Final conclusions require A/B measurement and engineering review.

04 / CORRECTIVE-ACTION COMPARISON

Explain the mechanism and side effects of every action.

Every corrective action states its mechanism, applicable band, layout conditions, potential side effects, and verification method—not merely a component name.

Common-mode choke (rule/common-mode-choke)

Mechanism: high common-mode impedance with low differential loss. Condition: sufficient impedance at 150 MHz. Side effects: bias saturation, differential loss, size, and cost. Verification: measure common-mode current before and after the choke.

Reduce harness length (rule/reduce-cable-length)

Mechanism: change electrical length to move away from resonance. Condition: vehicle packaging constraints. Side effect: resonance may shift upward and reappear. Verification: compare spectra in a harness-length A/B test.