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Energy lost by EM radiation per cm in air?

  1. Nov 20, 2015 #1
    Hey all, is there a formula that can calculate the energy losy by a photon travelling through air at 1 atm per meter given frequency? Any help apreciated.
     
  2. jcsd
  3. Nov 20, 2015 #2

    russ_watters

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    Photons do not lose energy when traveling - they are what they are.

    However, a photon may be absorbed and cease to exist.
     
  4. Nov 20, 2015 #3

    jtbell

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    Do you have a particular frequency range in mind? (radio, visible, X-ray, gamma-ray, ...?)
     
  5. Nov 20, 2015 #4

    sophiecentaur

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    If you google "atmospheric absorption" you may find out what you want. Your question is too unspecific for us to help you more.
    Perhaps you are not concerned with a single photon?
     
  6. Nov 20, 2015 #5
    Yea, but wouldnt it be absorbed and reemitted at lower energy on average a certain number of times or would that be too capricious to be used?

    Yea, microwave/radio
     
  7. Nov 20, 2015 #6

    sophiecentaur

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    So you are interested in radio wave propagation. There is loads of information about that and I recommend that you google appropriately to get some background and to find out the actual questions that need answering for your problem.
    The attenuation of the atmosphere varies wildly over the microwave region and also with water content. There isn't a number of formula that you can just plug into and get a reliable answer. There is a lot of Statistics involved. But there are many graphs (google Images) which could give you a clue about what to expect.
     
  8. Nov 20, 2015 #7
    Thanks :)
     
  9. Nov 20, 2015 #8

    davenn

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    as you have been told ... forget about individual atoms ... that's irrelevant

    ohhh and for the calc's below, anything less than a few 10's of metres is also going to be irrelevant
    as you would be dealing with near field effects which is isn't going to be helpful to you

    if you want to learn more on that google RF propagation, near field and far field


    OK that is relatively straightforward and is used all the time for us doing pathloss calculations between radio transmit and receive sites
    say example microwave links
    have a look at this site and it tells you all about FSPL ... Free Space Path Loss
    http://www.radio-electronics.com/info/propagation/path-loss/free-space-formula-equation.php

    This will serve well for line of sight paths and for frequencies up into the mid freq microwave bands ~ 10 GHz
    after 10GHz. there are additional significant atmospheric problems to deal with


    cheers
    Dave
     
  10. Nov 21, 2015 #9
    Thanks :)
     
  11. Nov 24, 2015 #10

    sophiecentaur

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    You should try to find stuff on 'Link Budgets". That takes everything into account; transmit power, feeder loss, antenna gain, path loss, spreading loss, etc etc and can give you a Carrier to noise ratio for the demodulated signal. Just what a chap needs. Path loss on its own is not actually a lot of use for designing a practical system.
     
  12. Nov 24, 2015 #11

    davenn

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    the 2 popular ones are Radio Mobile and UKW Tools
    I have used UKW tools for many years for my activities on 1296MHz and up to 24GHz

    it takes all those factors into account :smile:


    Dave
     
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