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Unlicensed Bands

  • 25-06-2007 2:48pm
    #1
    jhegarty
    Registered Users, Registered Users 2 Posts: 6,440 ✭✭✭


    Hello,


    Quick idiot question .... what bands can one transmit on (legally) without any license ?

    and what would have the longest range ?


Comments

  • #2
    Heathen
    Registered Users, Registered Users 2 Posts: 1,459 ✭✭✭Heathen


    CB 11 Meter band, and the range can be thousands of miles with the right propagation

    i think there may be other bands that things like cordless phones, garage door openers, etc that you could probably transmit, cb just seems to be handiest and more widley available, also a lot of different modes... am/ fm/ ssb/ usb/ lsb/ cw


  • #3
    watty
    Registered Users, Registered Users 2 Posts: 32,417 ✭✭✭✭watty


    CB, (allowed tall roof aerial), PMR446 about 5km no external aerial allowed. 49MHz toy walkie talkies about 0.1km.

    WiFi 2.4 and 6Ghz bands up to 100mW

    Video Analogue 2.4Ghz up to 500mW

    DECT is shortrange.


  • #4
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 92,367 Mod ✭✭✭✭Capt'n Midnight


    watty wrote:
    PMR446 about 5km no external aerial allowed.

    The limit on PMR 446 is Maximum Permitted radiated power (ERP)
    not EIRP so doesn't that mean you put them at the focal point of a corner reflector or satellite dish to increase the range.

    some limits are artificial , once you get to 54Mbs wifi the timing means you can't have more than ~300m with off the shelf stuff, whereas the 11Mbs stuff can go 8Km with suitable high gain antennas


  • #5
    watty
    Registered Users, Registered Users 2 Posts: 32,417 ✭✭✭✭watty


    Though 100mW power and a 26dBi gain MMDS aerial takes WiFi way beyond the legal EIRP. With that at both ends indeed you can get 12km, but you need to change the default timing or it won't work well beyond 5km.

    At 446MHz you need a very big dish, infact over 4 times the diameter of MMDS dish for same gain as it has at 2.4Ghz. Every time you double the frequency the dish is 4 times better. Except the accuracy has to be better and any holes smaller. Think how good a mirror for visible light has to be.


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