antenna stuff

Discussion in 'Wireless & RF Design' started by aac9876, Jan 23, 2007.

  1. aac9876

    Thread Starter Active Member

    Dec 9, 2006
    A yagi has elements that are recievers. they are .25 of a cycle..?? Why are they not a full cycle length.?
    Why are some Yags have smaller elements towards the end but others have elements
    that are all the same size..??
    Is a patch antenna a form of Yagi??
    The little patch antenna that comes with Satellite radios is what kind??
    They say to place it close to your FM antenna if you want to use the FM system for broadcasts. If the signal comes down as a modulated digital signal then where does the conversion take place. Does the signal go to the patch,then the conversion box, then back to
    the patch and then jump to the FM antenna??? If the digital signal just jumped to the FM
    antenna it wouldnt be intelligible..
    Why is a dish shape reflector with a yagi in the middle so much better than a straight yagi??
    I just read an aarticle that said if you are installing a dish antenna and you move it 1-2
    inches the wrong way you wont get any satellite signal. If thats so how thw hell can so
    many people in a city still zero in on the signal of one satellite?? Thanks:eek:
  2. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    Is there an online source that's making these claims?
  3. mrmeval

    AAC Fanatic!

    Jun 30, 2006
  4. beenthere

    Retired Moderator

    Apr 20, 2004

    About the satellite being available to many - we can all see the sun, too. It's further off than the geosynchronous satellite.

    You might be interested in reading up on antenna theory.
  5. Gadget

    Distinguished Member

    Jan 10, 2006
    Think of the satellite as a light bulb out in space, and the dish is a magnifying glass trying to focus that light onto a tiny spot (the LNB)..... the co-ordinates have to be fairly precise, and you need a bloody steady hand.
  6. subtech

    AAC Fanatic!

    Nov 21, 2006
    Hello aac9876
    To answer all of your questions here could get quite lengthy, so, let me dig up some links for you that will give you basic answers. Let's deal with the facts dealing with yagi antennas first.
    go here:

    I'll try to find a link on parabolic reflector antennas (dish antennas) next and post it here soon.
  7. subtech

    AAC Fanatic!

    Nov 21, 2006

    Here is another link that will give you a page which lists several articles
    that will explain much about parabolic reflectors, feeds, waveguide, and other
    aspects of the part of the electromagnetic spectrum which usually make use of "dish" antennas.
  8. subtech

    AAC Fanatic!

    Nov 21, 2006
  9. RAH1379

    Well-Known Member

    Dec 13, 2005
    the reason they use 1/4 wavelength for the driven elements is the impedance is easy to match to the feedline impedance,the different ratios of element length and element spaceings change the focus of the signal, and the bandwidth of the antenna. The amount of gain depends on how much the beam is focused just like a search light.