EMC and Transmitter Interference

Cross Modulation & Blocking

  • When a strong signal overloads an amplifier it can cause the gain of the amplifier to vary in time with its modulation, imposing its modulation on a wanted AM signal, e.g., TV video, as light and dark horizontal lines; lesser impact on FM signals
  • SSB is worst for this; interference from FM transmissions might go unnoticed
  • A strong signal may affect the receiver’s AGC circuits, or overload an amplifier stage, turning down gain and causing the wanted signal to become weak or / and noisy; this is known as desensing or blocking
  • It is more common from FM or data modes