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What's different between a receiver & transmitter antennas?

  1. Aug 15, 2015 #1
    Hello,

    I'm currently working on satellite model for high-school compatition, and i'm not sure if there's a visual differance between a reciver & transmiter antenas (on satellites)...
    Also, is it possible to satellite to recive a radio wave information from another satellite

    Thank you
     
  2. jcsd
  3. Aug 15, 2015 #2
    I think there is no visual difference from one to another, but a satellite receiving radio wave information from another one, it's possible yes, some satellites are connected to transfer information one through another to then send it back to earth at another location ex: From one side to another, only 1 satellite can't do the work alone.
    Satellites are connected like a network, they receive and send informations from earth one to another until one sends it back again to earth.
    But to the visual difference, i think there isn't one, i don't know for sure.
     
  4. Aug 15, 2015 #3
    Thank you very much :)
     
  5. Aug 15, 2015 #4

    berkeman

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    Depending on the application, I can think of a couple of potential differences. Can you say what they might be? (Hint -- think about different applications that satellite communication support) :smile:
     
  6. Aug 15, 2015 #5

    berkeman

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    Also, since this is for your schoolwork project, I would normally move this thread to the Homework Help section of the PF. I'll allow it to stay here in the EE forum for now, as long as posters remember to have you do the bulk of the work on this question... :smile:
     
  7. Aug 15, 2015 #6

    sophiecentaur

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    Is your question actually about transmit and receive antennae on board the satellite? Are we dealing with broadcast or communication antennae here? Makes a big difference to the designs.
    Have you looked at images (Google) of satellite transmit and receive dishes? You will notice they are the same shape (parboloids) and the differences will be mainly in diameter - depending on the power of the transmitter used and how strong the received signal is.
    This could be a very sophisticated question and it's potentially way beyond High School level but, if you are concerned with TV satellite mounted antennae then you have to think about Footprint for the transmitting dish. Beam needs to be narrow (perhaps 1000km footprint on the surface and a distance of about 35000km) to make sure the satellite only serves a restricted area of the Earth. There are only so many channels available and the channels have to be re-used for nearby reception areas. How does the signal get up to the satellite? An Earth station can have a more powerful transmitter and that means the receive antenna can have lower Gain.
    Give us some feedback about the details of your project brief.
     
  8. Aug 15, 2015 #7
    what\s a 1000 km footprint?
     
  9. Aug 15, 2015 #8

    nsaspook

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    For a satellite it's the coverage area on earth from a signal beamed from satellite to earth from a transponder or group of transponders using an antenna.
    It might be a traditional parabolic reflector or a modern phased array used to electronically steer the focus and direction of the beam to earth or on the earth to receive that signal. The size of that footprint depends on both the transmit and receive antenna gain (size), transmit power, receiver sensitivity, type of modulation and a host of other factors.

    For an example most large DBS commercial networks have two types and typically use much higher frequencies for the down-link (KU and up 12-20+ GHz band for smaller antennas with high gain for consumers) than the up-link (C 5-7 GHz band large dishes for the providers that also provide resistance to atmospheric effects like heavy rain)
    1. A wide coverage beam(s) on one or more transponders on the same channel or group of channels for general coverage of a wide area footprint.
    Dual_Matrix_Coverage_Map_02.jpg
    1. Spot beams on other transponder channels designed to provide specialized coverage (like local TV channels)
    for groups of large cities each with a much smaller footprint
    27DTVSpotBeammap.png

    and yes, you can and do have satellite to satellite communications on some systems.
     
    Last edited: Aug 15, 2015
  10. Aug 15, 2015 #9
    I assume it is a 1000 km diameter circle target on earth, then. Rather than a 1000 km2 target?
     
  11. Aug 15, 2015 #10

    nsaspook

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    That should be the Radius distance (I think, it's been a while since I worked with this stuff) but it's not always a circle.
     
    Last edited: Aug 15, 2015
  12. Aug 16, 2015 #11

    Baluncore

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  13. Aug 16, 2015 #12

    sophiecentaur

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    That's certainly the answer in a nutshell. The supplementary is "Transmitting to what and Receiving from what?"
    Link budgets rule.
     
  14. Aug 16, 2015 #13
    Thank you all, it was very helpful :smile:
     
  15. Aug 17, 2015 #14

    berkeman

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    But you didn't answer my question...
     
  16. Aug 18, 2015 #15

    sophiecentaur

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    But does it make any significant distance in the context? We are talking in terms of Orders of Magnitude. When Engineers need km accuracy they use km and when they need mm accuracy, they talk in mm. Life's too short, chaps.
     
  17. Aug 18, 2015 #16

    sophiecentaur

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    I think we scared him off!! :smile:
    Engineering replies can be a bit overwhelming.
     
  18. Aug 18, 2015 #17
    Sorry, I didn't see your comments until now...
    I'm not sure yet about all the details, it's a team project, and I'm in charge only on the model design... So i don't know about any difference between them, or even if there is one...:frown:
     
  19. Aug 18, 2015 #18

    berkeman

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    Well, most satellite antennas will be parabolic dishes. What are most land-based, mobile antennas?
     
  20. Aug 18, 2015 #19
    I'm not sure... I think they're also parabolic, aren't they?
     
  21. Aug 18, 2015 #20

    davenn

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    you sure ? :wink:

    what sort of antenna does your car radio have?, what about the antennas on vehicles for CB, Ham or commercial
    radio communications ?

    The main places for terrestrial based radio systems using parabolic dishes is
    for microwave links between sites

    have a look on a cell (mobile) phone tower
    you will see several large vertical antenna arrays for communicating with the mobile phone you carry
    there will also be up to 3 small parabolic antennas for microwave band linking to other cellular towers,
    generally in the 18 - 50 GHz range


    Dave
     
    Last edited: Aug 18, 2015
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