Transmitter Harmonics & Spur Calculator

Harmonic emission regulation dates to the 1912 International Radiotelegraph Convention, which established the first treaty on radio interference. The US Radio Act of 1927 codified harmonic-suppression requirements for commercial broadcasters. Modern FCC Part 15 (unlicensed) and Part 97 (amateur) limits formalized in the 1980s specify out-of-band emissions as dBc below the fundamental or dBm absolute.

The 1990s spectrum-crowding drove harmonic specs tighter. Cellular transmitters had to suppress 2nd-harmonic emissions that would otherwise jam GPS (1.575 GHz — close to 2× 800 MHz GSM). WiFi 2.4 GHz 2nd harmonics land near 4.8 GHz (inside WiFi 5 GHz), so radios need sharp bandpass filters between PA and antenna.

Modern multi-band radios solve the harmonic problem with switchable filter banks (one per band) or with tunable filters built into the PA output. GaN PAs with >60 dB ACLR (adjacent channel leakage ratio) made post-PA filtering less critical, but harmonic suppression still requires dedicated filter stages in most production radios.

Enter the carrier frequency (with SI suffixes) and the number of harmonics to compute (2-20). The tool lists each harmonic frequency and checks whether any fall inside sensitive bands: GPS L1 (1.575 GHz), GPS L2 (1.227 GHz), aeronautical VHF (108-137 MHz), AM broadcast (535-1705 kHz), FM broadcast (88-108 MHz), cellular LTE bands.

Red-flagged harmonics tell you which filter stages to emphasize in your RF chain. Use this alongside your PA datasheet\'s 2nd/3rd harmonic levels to predict post-filter emissions. For production compliance, measure with a spectrum analyzer — calculated predictions are accurate only if PA nonlinearity is well-characterized. Everything runs client-side.