Whitepaper
Indirect Lightning Testing using Waveform 3
This EMC Partner whitepaper addresses a fundamental technical limitation in performing indirect lightning testing using Waveform 3 (WF3) at 10 MHz as defined in RTCA/DO-160 and EUROCAE ED-14. WF3 is a damped sinusoidal waveform derived from lightning transients near aircraft, and its frequency is inversely proportional to cable length. While WF3 at 1 MHz presents no serious challenges for PIN injection or cable bundle testing — the required generator impedance of 25 ohms and short-circuit current of 128A are achievable — applying WF3 at 10 MHz introduces significant practical problems. Load impedance increases by a factor of ten between 1 MHz and 10 MHz, and a 1-metre coaxial cable more than doubles the effective test equipment impedance at 10 MHz, distorting the waveform and severely limiting achievable current. When a coupler is added for cable bundle testing, the required series inductance to maintain the correct oscillation frequency results in very high impedances, meaning that reaching the DO-160 limit current of 640A at level 5 would require generator charging voltages of tens of kilovolts — impractical and potentially damaging to the device under test. The paper concludes that the DO-160 provision allowing the generator to not produce the associated limit current in such cases should be rigorously applied, and presents the EMC Partner AVI-LV3 combined generator as a practical compliant solution.