sentinal-5
sentinal-5
52 / 4
13th January
13th January
i made this mostly to answer a question from NoVIcE about the spherical vs parabolic shape of antenna reflectors. this type of antenna uses a spherical reflector and you probably have one outside your house if you get sattelite tv.
dish radical communication radio science

Comments

  • sentinal-5
    sentinal-5
    15th January
    TL;DR spherical dish is only good for listening, but you can aim it by moving your reciever within the dish.
  • sentinal-5
    sentinal-5
    15th January
    PortalPlayer if you want to have Tx capability yes you need a paraboloid dish, but for Rx only a spherical reflector is cheaper, works almost exactly as well due to the extremely short distance, and allows for multiple recievers per dish. the Arecibo space telescope is a great example of a spherical reflector, but they use theirs to allow the reciever to be moved against a stationary reflector.
  • PortalPlayer
    PortalPlayer
    15th January
    NoVIcE: small antennae are offset so that the feed horn apparatus doesn't block the signal. They're not common for larger dishes because the shape is harder to manufacture. I don't know what this stuff about them being spherical is about, because spheres don't focus properly.
  • PortalPlayer
    PortalPlayer
    15th January
    Offset feed dishes are still parabolic, they just use the half of the curve on one side of the focus. No way would you use a spherical dish.
  • mccafferty2
    mccafferty2
    15th January
    This is why i love tpt
  • NoVIcE
    NoVIcE
    15th January
    Hey, why do i see spherical offset antennas so often, are they cheaper than parabolic ones? It seems strange because for a parabolic one, it looks like you will need less precision to place the transmitter/reciever. Thats my guess IMO. So, why arent parabolic more abundant?
  • Security-Drone
    Security-Drone
    15th January
    "rrrrrefraction is dhe biinding of a rrray ohf lyght" as my dad's old science prof used to say. (Transliteration: Refraction is the bending of a ray of light.- He had dodgy pronunciation) But I see what your getting at. :P
  • sentinal-5
    sentinal-5
    14th January
    in 2d like TPT you'd be absolutely right, but prisms only allow for a 1d transformation, whereas with a 3d dish reflector you can capture a 2d plane of signal and compress it all into a point focus with just one transformation. there are certain types of antenna that use lenses, but obviously that isn't as simple in RF as it is in visible light. RF lenses actually end up being a series of concentric spheres of extremely specific dimentions.
  • SpamBot-01
    SpamBot-01
    14th January
    Frankly I think prisms would be a better way to go but I see what your getting at. :P
  • sentinal-5
    sentinal-5
    14th January
    there are a lot of really fascinating things about rf hardware i'd love to post. unfourtunately i'm really ill at the moment so they're going to have to wait. oh and then there's the fact that i'm not even sure i can build a working gregorian offset reflector in TPT lol.