Radio Frequency Emissions

Radio Frequency Emissions (avionics/do160/radio-frequency-emissions)

Use when the task is planning and checking the DO-160 section 21 equipment emission test of airborne equipment: CE102 conducted emissions over 10 kHz to 10 MHz and RE102 radiated emissions over 2 MHz to 18 GHz. This leaf converts measured amplitudes into the dBuV and dBuV/m scales, applies the reference-only typical limit model for the installation category, computes the emission margin at every frequency, finds the worst case frequency, and returns the pass or fail verdict that gates the EMC qualification. It is implemented in pure Python, stdlib only. The immunity counterpart (DO-160 section 20, the radio-frequency-susceptibility leaf) owns the radiated and conducted susceptibility tests of the same equipment; this leaf is strictly the emission side, section 21.

Domain quick reference

• Conducted emission level: dBuV = 20 * log10(V_uV), with V_uV the measured amplitude in uV (volts * 1e6). Anchors: 1 V is 120 dBuV, 1 mV is 60 dBuV, 1 uV is 0 dBuV. dbu_v_from_volts and volts_from_dbu_v convert both ways.
• Radiated emission level: dBuV/m = 20 * log10(E_uV/m), with E in V/m. Anchor: 1 V/m is 120 dBuV/m. dbu_v_per_m_from_v_per_m converts one way; the RE102 antenna measurement is then expressed in dBuV/m.
• CE102 limit (reference-only typical, NOT the normative RTCA curve): piecewise constant over the test band, 78 dBuV below 100 kHz, 60 dBuV from 100 kHz to 2 MHz, 70 dBuV from 2 MHz to 10 MHz. The normative conducted emission limit comes from the current DO-160 revision. ce102_limit_db(freq_hz, category) applies the curve; the category is validated and carried through but does not shift this simplified model.
• RE102 limit (reference-only typical floors): category A 24 dBuV/m, category B 34 dBuV/m, category C 44 dBuV/m across 2 MHz to 18 GHz. The normative radiated emission curve varies within the band and must be read from the current DO-160 revision. re102_limit_db(freq_hz, category) applies the floor.
• Emission margin: margin_db = limit_db - measured_db at each frequency; a negative margin is a fail. conducted_emission_margin and radiated_emission_margin evaluate it on the dBuV and dBuV/m scales.
• Worst case: the frequency carrying the minimum margin across the sweep, returned by worst_case_frequency(freqs, margins).
• Verdict: pass when the minimum margin is >= 0 dB, returned by emission_verdict(margins, freq_hz, category, kind) as a dict with the pass flag, worst margin, worst frequency, and category. A margin band of >= 6 dB is a typical engineering recommendation, reference-only, not a hard RTCA requirement.
• Source sanity check: E (V/m) = sqrt(30 * P_erp) / d for a characterized radiating source, the inverse-square far-field relation. field_strength_from_erp returns V/m; convert with dbu_v_per_m_from_v_per_m to compare against RE102. This checks the emission source level, it does not size an immunity amplifier.
• Units: voltage in V, field in V/m, frequency in Hz, ERP in W, distance in m, levels in dBuV and dBuV/m.

Workflow

1. Classify the equipment: pick the installation category (A, B, or C in this reference-only model) and the emission side under check, CE102 conducted or RE102 radiated.
2. Convert the measured amplitude: dbu_v_from_volts for a conducted measurement in volts, dbu_v_per_m_from_v_per_m for a radiated field measurement in V/m, so every measurement is on the dB scale of its limit curve.
3. Apply the limit at each measured frequency with ce102_limit_db or re102_limit_db for the category.
4. Compute the emission margin per point with conducted_emission_margin or radiated_emission_margin (limit minus measured).
5. Find the worst case frequency with worst_case_frequency over the sweep.
6. Judge the equipment with emission_verdict(margins, freq_hz, category, kind), where kind is conducted/CE102 or radiated/RE102.
7. When an antenna is characterized, sanity-check the radiating source level with field_strength_from_erp before blaming the equipment.
8. Confirm the deterministic checks with the contract test scripts/test_radio_frequency_emissions.py.

Worked example

Category A equipment, representative measurements.

• Conducted: 72 dBuV measured at 150 kHz. The reference CE102 curve gives 60 dBuV at 150 kHz, so the margin is 60 - 72 = -12 dB, a fail.
• Radiated: 40 dBuV/m measured at 100 MHz. The RE102 category A floor is 24 dBuV/m, so the margin is 24 - 40 = -16 dB, a fail.
• Conducted sweep verdict: measured 60, 72, 68 dBuV at 50 kHz, 150 kHz, and 5 MHz against the CE102 curve 78, 60, 70 dBuV gives margins +18, -12, +2 dB. worst_case_frequency returns 150 kHz at -12 dB and emission_verdict returns pass False with worst margin -12 dB at 150 kHz.
• Radiated sweep verdict: measured 15, 40, 20 dBuV/m at 10 MHz, 100 MHz, and 1 GHz against the 24 dBuV/m floor gives margins +9, -16, +4 dB. emission_verdict returns pass False with worst margin -16 dB at 100 MHz.
• Source sanity check: 100 W ERP at 10 m gives E = sqrt(30 * 100) / 10 = 5.477 V/m, which is 134.77 dBuV/m at the antenna, far above any category floor, so the source itself must be screened or relocated before retesting the equipment.

Verification

• Confirm dbu_v_from_volts(1.0) returns 120 dBuV and volts_from_dbu_v(120.0) returns 1 V (round trip holds).
• Confirm dbu_v_per_m_from_v_per_m(1.0) returns 120 dBuV/m.
• Confirm ce102_limit_db(150e3, "A") returns 60 dBuV and re102_limit_db(100e6, "A") returns 24 dBuV/m.
• Confirm conducted_emission_margin(72.0, 60.0) returns -12 dB and radiated_emission_margin(40.0, 24.0) returns -16 dB, and that emission_verdict over those sweeps reports fail with the worst case at the minimum margin frequency.
• Confirm every negative or zero amplitude, every non-positive frequency, every frequency outside the CE102 or RE102 test band, every unsupported category, every unknown kind, and every empty or mismatched sweep raises ValueError.
• Run the contract test offline: python3 scripts/test_radio_frequency_emissions.py (32 tests, deterministic).

Related leaves

• avionics/do160/radio-frequency-susceptibility: the DO-160 section 20 counterpart that owns the radiated and conducted susceptibility tests of the same equipment (section 21 here is the emission side).
• avionics/do160/electrostatic-discharge: DO-160 section 25 ESD test levels and waveforms, another equipment-level EMC environment.
• avionics/do160/lightning-protection: DO-160 sections 22 and 23 lightning induced transient and direct effects environments.

Pitfalls

• Mixing linear and dB scales: every measurement must be converted to its dB domain first (dbu_v_from_volts with volts * 1e6 for conducted, dbu_v_per_m_from_v_per_m for radiated); feeding volts straight into a dBuV limit comparison misplaces the anchor by 120 dB at 1 V.
• Flipping the margin sign: margin is limit minus measured, so a negative margin is a fail - computing measured minus limit inverts the pass/fail verdict for every sweep point.
• Applying the wrong curve side: CE102 conducted limits and RE102 radiated category floors are different functions of frequency, and emission_verdict needs the matching kind (conducted/CE102 or radiated/RE102); a radiated measurement checked against the CE102 curve is meaningless.
• Quoting the simplified curves as normative limits: the CE102 band curve and the RE102 category A/B/C floors here are reference-only typical values, not the current RTCA/DO-160 section 21 table - the real curve varies within the band and must be read from the current revision before any qualification call.
• Misapplying the ERP sanity check: field_strength_from_erp checks the radiating source with the inverse-square far-field relation (100 W ERP at 10 m is 134.77 dBuV/m) - it does not size an immunity amplifier; amplifier sizing belongs to the radio-frequency-susceptibility leaf.
• Demanding a hard 6 dB band: the >= 6 dB margin band is a typical engineering recommendation, not an RTCA requirement; the verdict in this leaf passes at a minimum margin of >= 0 dB, so treat 6 dB as design guidance, not a failure criterion.

Behavior contract (gate 3)

Run the deterministic contract test (stdlib unittest, offline):

python3 scripts/test_radio_frequency_emissions.py

The test covers the dBuV and dBuV/m conversions and their anchors, the reference-only typical CE102 band curve and RE102 category floors including band edges, the worked example margins (-12 dB conducted at 150 kHz, -16 dB radiated at 100 MHz, category A), pass and fail verdicts over single points and sweeps, worst case frequency selection with tie handling, the ERP far-field sanity check with inverse-square scaling, and ValueError rejection of non-physical inputs, out-of-band frequencies, unsupported categories, unknown kinds, and empty or mismatched sweeps.

Compliance

• Standards referenced, not reproduced: DO-160 (RTCA, EUROCAE twin ED-14) section 21 is referenced by name. The CE102 and RE102 limit values in this leaf and its logic module are paraphrased reference-only typical values, explicitly NOT the normative RTCA table; the normative limits come from the current RTCA/DO-160 revision and must be verified against it before any qualification decision (standards-map.yaml).
• compliance: STANDARDS-REF, gated: false.