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Functions of satellite TV and satellite

Discussion in 'Radio and Communications' started by Willen, Jun 10, 2012.

  1. Willen

    Willen Well-Known Member

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    I don't have such satellite TV receiver yet but now a days, a tv programme transmitted from satellite can be pause and play at home. How it can be possible? What is the system? Please!
     
    Last edited: Jun 10, 2012
  2. picbits

    picbits Well-Known Member

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    They normally have a hard drive inside the receivers which buffers / stores the video stream.

    There is also Video on Demand which streams the video signal via the internet - much like Youtube.
     
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  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes, it's a HDD in the receiver - but only PVR's do this, not plain receivers (exactly as with Freeview ones).
     
  4. dave

    Dave New Member

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  5. Willen

    Willen Well-Known Member

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    It means, when we want to Pause or Record whole day's program, Should we have to keep ON the receiver, to record the program continuously transmitted from station? Can we able to copy and paste these recorded videos into PC?
     
    Last edited: Jun 11, 2012
  6. picbits

    picbits Well-Known Member

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    Yes - if you turn the power off then it won't be able to record. Most will come out of standby to record a program then go into standby when they are finished though.
    It depends on what recorder you have - do you have the make and model number ? Most with internal hard drives will not allow you to access the data on a PC. Some which are compatible with external hard drives may allow this function.
     
  7. Willen

    Willen Well-Known Member

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    Hi again after 4 years(in the thread),
    As I know the TV satellite station in space is placed in zero gravity and it's not running like GPS satellites run. Then when the earth goes away to round the sun then how it follows the earth? If the motion of the satellite has been set same as earth, then how they make it possible? It needs to round the earth in 24 hours and need to round the sun in 365 days same as earth? How they set the motion of the satellite?
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Simple answer - GRAVITY.
     
  9. Willen

    Willen Well-Known Member

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    But the TV satellite are placed in 'zero gravity', isn't it?
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No - the earth's gravity keeps satellites (including the moon) in place, the suns gravity keeps all the planets in place.
     
  11. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    And their velocity keeps them at their respective distances from one another.
     
  12. Willen

    Willen Well-Known Member

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    But why things float in space (lets say between the earth and the moon)?
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I suggest you try googling :D
     
  14. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Witten,

    Standing still, swing an object (like a ball), that is attached to a string, around yourself. The ball is in an orbit around you, right?

    It stays away form your body, rotating in a circle around you. Similar to the graphic below:
    upload_2016-3-14_11-13-43.png
    Or, with a satellite:
    upload_2016-3-14_11-1-48.png

    In this example, you are the Earth (the source of the gravity), the string is equivalent to gravity and the ball, which is moving in a circle and so has velocity, is the satellite.

    This is also true on the Earth and the Moon, or the Sun and Earth or our Solar System and our galaxy!

    The above are Non- synchronous examples.

    Now, while swinging the ball, rotate your body as well, keeping your eyes on the ball - the ball is now in a synchronous orbit: you AND the ball are rotating at the same angular speed.

    Was this helpful?

    If so, we can move on to :zero-gravity" and the term "Float" in space.
     
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  15. JimB

    JimB Super Moderator Most Helpful Member

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    How mathematical do you want to get?

    The gravitational force of attraction between two objects is given by:

    F = (G .m.M) / r^2

    where G is the Gravity Constant (6.674 x 10^-11 N m^2 kg^-2)
    m is the mass of the smaller body
    M is the mass of the larger body
    r is the distance between the centres of mass of the two bodies

    The centrepetal force acting on a body in circular motion is given by:

    F = (m.V^2)/r
    where m is the mass of the body
    V is the instantaneous velocity of the body
    r is the radius of the circle

    Putting these two equations together we end up with:

    V^2 = G.M/r
    G.M is a constant, mass of the earth times the gravity constant

    Putting this into words, the lower the satellite orbit (r) the faster the satellite must move (V)
    So for a geosynchronous orbit, the velocity must be such that the satellite completes the distance of its orbit in 24 hours.

    So from all this, when you know the mass of the earth and the gravity constant, you can calculate how fast and at what height the satellite must move to stay in a fixed position in the sky.


    As for a small object half way between the earth and the moon, the gravity force on it are very small, so it will not go far very quickly.
    But, over time it will move, either it will drift off into space, or it will eventually fall to earth.


    In this case, yes it is rocket science! :)

    JimB
     
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  16. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    The simple answer:
    1) The earth pulls objects in. ( Gravity ) Just like you are pulled down right now. If you are far away from earth the pull is less.
    2)Objects want to go in a straight line. It is hard to turn a corner. It is hard to go in a circle. Think about riding in a car, turn hard and the people (in the car) are pulled to the outside of the turn.
    1+2) Earth pulls down. & Orbiting (going in a circle) pulls out. "float" is when ( pull down = pull out )
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I can't remember exactly but doesn't a satellite travel at 17,000 miles per hour so that it stays over one spot on Earth as the Earth spins around each day? It is called a Geosynchronous Earth Orbit.
    But some people still think the Earth is flat and stationary. They believe the heavens are spinning around us.
     
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  18. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Yes, the concept was first proposed by Arthur C. Clarke in 1945.
    He was a true visionary science fiction writer and actually included some real science in his fiction.
     
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  19. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    I can not get the flat idea to work.
    I have argued for the idea that the world is hallow and we line on the inside. The universe is in a time warp in the center. (I don't believe this like I don't believe in a 6000 year old world) It is an experiment in proving things that are wrong. lol
     
  20. Dr_Doggy

    Dr_Doggy Well-Known Member

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    the simple answer is that the satellite falls towards the earth at the same velocity it is traveling away from it...and no air resistance to slow it down...
    ....my belief is that there is a lucky guy sitting in the middle who gets to push alot of buttons!

    here's one,lol...
     
  21. Willen

    Willen Well-Known Member

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    I know a satellite rotates (rotating satellite like some satellite phone stations) in its orbit due to centrifugal force and gravity of centre object. But how they pause a satellite (which do not rotates, like TV satellite) in zero gravity? How they take reference in space to lock the movement?
     

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