Radio Theory 5

$Signal Loses The atmosphere can affect radio signal paths at lower frequencies, especially below 30 -50MHz, the ionosphere has a significant effect, reflecting (or more correctly refracting) them back to Earth. At frequencies above 50 MHz and more the troposphere has a major effect, refracting the signals back to earth as a result of changing refractive index. For UHF broadcast this can extend coverage to approximately a third beyond the horizon. Radio Interference Radio Interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. Electromagnetic Interference at 2.4 GHz can be caused by 802.11b and 802.11g wireless devices, blue-tooth, baby monitors and cordless phones, video senders, and microwave ovens. Source of Radio Interference Switching loads such as electric motors, transformers, heaters, power supplies, etc. all cause electromagnetic interference especially at currents above 2 Amps. Poor shielding will lead to unwanted emissions; electromagnetic Interference at 2.4GHz can be caused by: 802.11b, 802.11g, 802.11n wireless devices blue-tooth devices baby monitors and cordless phones microwave ovens Reducing Radio Interference A highly directional receiver, such as a parabolic antenna or a diversity receiver, can be used to select one signal in space to the exclusion of others. Spread spectrum and frequency hopping techniques can be used with both analog and digital signaling to improve resistance to interference. Use an RF spectrum analyzer to check for any unusually high radio signals in the frequencies you are using (2.4Ghz) Shielding - contains unwanted signals from electrical switching sources eg. Motors, transformers etc Use Filters - low pass filters, high pass filters, band pass filters$