<![CDATA[Abstrak. Tujuan penelitian ini adalah untuk melihat bagaimana efek distorsi harmonik total (THD atau Total Harmonic Distortion) berdampak pada akurasi pengukuran penerima di sistem Instrument Landing System (ILS). Dalam lingkungan bandara, perangkat listrik non-linear dapat menyebabkan distorsi harmonik, yang berdampak pada kualitas sinyal navigasi yang diterima pesawat. Ini terutama berlaku untuk parameter DDM (Difference in Depth of Modulation). Metode kuantitatif eksperimental digunakan; sinyal ILS yang terdistorsi disimulasikan menggunakan GNU Radio dan diuji dalam situasi nyata menggunakan HackRF One dan Portable ILS Receiver. Ada gangguan dalam bentuk harmonik orde ke-3, 5, dan 7 pada frekuensi 90 Hz dan 150 Hz, serta frekuensi tambahan seperti 30 Hz, 60 Hz, dan 120 Hz. Ini ditampilkan sebagai 1%, 3%, dan 5% THD, dengan variasi +10% dan -30%. Meskipun terdapat gangguan harmonik hingga 5% THD, hasil simulasi menunjukkan bahwa nilai DDM dan SDM tidak mengalami perubahan yang signifikan, menunjukkan bahwa gangguan ini tetap berada dalam batas toleransi sistem ILS. Penelitian ini menunjukkan bahwa, selain pengujian spektrum dan inspeksi penerbangan sebagai bagian dari pengujian ground check, evaluasi lingkungan elektromagnetik di bandara sangat penting untuk menjamin keandalan sistem ILS. Evaluasi toleransi memastikan bahwa sistem beroperasi secara optimal meskipun terpapar distorsi harmonik.Abstract. This research aims to analyze the effect of harmonic distortion (Total Harmonic Distortion/THD) on the measurement accuracy of receivers in the Instrument Landing System (ILS). Harmonic distortion may originate from non-linear electrical devices in the airport environment and interfere with the quality of navigation signals received by aircraft, especially in terms of DDM (Difference in Depth of Modulation) . A quantitative experimental approach was employed through ILS signal simulation using GNU Radio and practical testing using HackRF One and Portable ILS Receiver. Interference was injected in the form of 3rd, 5th, and 7th order harmonics from 90 Hz and 150 Hz signals, along with additional frequencies (30 Hz, 60 Hz, 120 Hz) and THD variations of 1%, 3%, 5%, with extra tests at 10% and 30%. Simulation results show that harmonic interference up to 5% THD did not cause significant deviations in DDM or SDM and remained within ILS system tolerances. However, higher THD and additional frequencies caused small fluctuations that were not detected during ground checks but had observable effects during flight checks, as evidenced by signal anomalies during aircraft approach. This research emphasizes the importance of spectrum analysis and flight inspection as complements to ground checking and highlights the need for comprehensive electromagnetic evaluation at airports to ensure the reliability of ILS systems. A tolerance evaluation method was applied to assess whether the system remained functional under harmonic exposure.]]>
