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Homework Help: Weather and telecommunications

  1. Mar 9, 2005 #1
    Why/how does weather affect telecommunications? The photons in radio waves can pass through matter, such as human bodies and concrete, but they seem to be affected by weather conditions. Why is this, or is my reasoning flawed?
  2. jcsd
  3. Mar 9, 2005 #2
    Because large storms produce lightening, which is just an enormous electrical discharge. The electric field produced by lightenings is enough to cause disruption to radio and tv. Also weather can have a purely physical effect on telecommunications, damaging/destroying masts etc.
  4. Mar 10, 2005 #3
    Some radio waves bounce between the Earths surface and the ionosphere (I hope that's the right portion of the atmosphere I'm referencing), sometimes called a bounce or skip. Different frequency radio waves are absorbed, reflected or passed by different portions of the atmosphere. Expansion and contraction causes the angle of the radio wave front (especially in the HF frequency) to bounce at higher or lower angles sometimes changing how far away you can pick up a radio station (this is also why it's a regulation in the U.S. that AM (operate in the VHF range) radio stations reduce their output power in the evening).

    There's also such a thing called atmospheric ducting. THis is when a weather or storm front stretches accross a particular region and causes radios that would normally never be able to communicate or interfere with each other (due to being out of range) to do just that.
    Ham radio groups will watch weather reports and try and see who they can contact during these weather events.
    It's also been known to cause radio repair techs to go nuts trying to figure out where the intermittent interference is coming from in their area and make the same techs look like a BS artists trying to explain it to a non-technical person.
  5. Mar 10, 2005 #4


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    Staff: Mentor

    I can answer the "why are telecommunications affected by weather conditions". It's called "rain attenuation". In the case of wireless (broadband) and satellite communications, absorption is the major issue. Rain, ice crystals, snow & fog will absorb some of the radio waves, they can also scatter the waves. This causes attenuation of the signal (drop in the strength of the signal).

    The higher the frequency, the greater the attenuation. Lower frequencies have longer wavelengths and are less likely to be affected. Telecommunication companies will study the weather in each location they are transmitting and design the local network accordingly.

    When I design microwave (wireless broadband) networks for my clients, I have data available to me for each city that allows me to tell my clients how far he can optimally send a signal before having to bounce it. The distance is based on the worst weather conditions in the last 50 years. Different companies use different criteria.

    As for your second question "The photons in radio waves can pass through matter, such as human bodies and concrete, but they seem to be affected by weather conditions." If the atmosphere that the radio signals passed through were filled with human bodies and concrete, you would notice that they affect the signal as weather does, likely much more significantly. :wink: So your thinking is correct. Telecommunications of radio signals do not pass through these solid objects during the long distance transmission portion. Once it gets to your home, then the density of materials play a role, you may find a radio signal is weaker in one room than another, or your cell phone doesn't work in an elevator.

    I don't know if this helped or not.
  6. Mar 10, 2005 #5


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    Two answers for two separate frequency ranges. Francis's for your lower frequency transmissions and Evo's for your microwave transmissions (Ku band, I would guess).

    The attenuation Evo talks about is because of the harmonic frequency of different subtances. If you're transmitting at the harmonic frequency of water molecules, you wind up just oscillating the water vapor instead of transmitting an intelligent signal. In fact, while most frequency bands are designated by just one letter, they split the K-band up into two frequency bands when they realized this would happen. Now, you have Ku (under the water absorbtion band) and Ka (above the water absorbtion band). The closer you are to the divide, the more problems you have.
  7. Mar 10, 2005 #6


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    To take it a bit further, the size of the raindrop in relation to the wavelength of each frequency that passes through it is of importance. Any drop of rain in the path of the signal which approaches half the wavelength in diameter can cause attenuation.
  8. Mar 10, 2005 #7
    Thank you all very much. Great answers, very helpful.
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