Intermodulacja
Widmo częstotliwościowe z widoczną intermodulacją dwóch sygnałów o częstotliwościach 270 i 275 MHz. Wynik intermodulacji widoczny dla częstotliwości 280 MHz i 265 MHz.
Intermodulacja – proces, który zachodzi w nieliniowym urządzeniu lub ośrodku transmisyjnym, w sytuacji, gdy składowe widma sygnału lub sygnałów wejściowych oddziaływają na siebie i powstają w rezultacie nowe składowe o częstotliwościach równych kombinacji częstotliwości wejściowych składowych widma ze współczynnikami całkowitymi[1].
Zobacz też
- modulacja skrośna
- zniekształcenia nieliniowe
Przypisy
- ↑ PN-T-01030:1996 Kompatybilność elektromagnetyczna. Terminologia
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RF Intermodulation at 280 MHz.png
Autor: Nader Moussa, Licencja: CC-BY-SA-3.0
Frequency Spectrum of intermodulation distortion in a radio-frequency signal passed through the linear broad-band amplifier I built. The process of intermodulation is due to third-order harmonics of closely spaced signals. I tested this phenomenon with two signals: a Local Oscillator (LO) at 270 MHz, +0dBm, and an RF signal at 275 MHz. (Closer spacing would push the limitations of the RF spectrum analyzer resolution). Clear intermodulation products were seen at 265 and 280 MHz. As seen on the attached graph, the intermodulation power is 55.66 dB lower than the signal power. This graph nicely shows our desired signal peaks, as well as the side-band intermodulation. These closely spaced distortions would likely interfere with our signal, since it would be difficult to build a high-quality filter to cancel them out in our application. However, their overall power is more than 50 dB below the desired signal, which was sufficiently low for our purposes. We used this measurement to estimate the IP3 (third order intercept point) parameter.
Autor: Nader Moussa, Licencja: CC-BY-SA-3.0
Frequency Spectrum of intermodulation distortion in a radio-frequency signal passed through the linear broad-band amplifier I built. The process of intermodulation is due to third-order harmonics of closely spaced signals. I tested this phenomenon with two signals: a Local Oscillator (LO) at 270 MHz, +0dBm, and an RF signal at 275 MHz. (Closer spacing would push the limitations of the RF spectrum analyzer resolution). Clear intermodulation products were seen at 265 and 280 MHz. As seen on the attached graph, the intermodulation power is 55.66 dB lower than the signal power. This graph nicely shows our desired signal peaks, as well as the side-band intermodulation. These closely spaced distortions would likely interfere with our signal, since it would be difficult to build a high-quality filter to cancel them out in our application. However, their overall power is more than 50 dB below the desired signal, which was sufficiently low for our purposes. We used this measurement to estimate the IP3 (third order intercept point) parameter.