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VHF Ethernet

Discussion in 'Electronic Design' started by [email protected], Feb 25, 2007.

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  1. Guest

    Hi

    I would like some help for creating wireless ethernet network using
    VHF radio with frequency range of 130MHz-18MHz. The distance supported
    shall be upto 100km LOS. Kindly advise on industry products available
    for such option.

    Regards

    Khan
     
  2. You need a license to transmit.
    130MHz (18MHz bandwidh?) are you crazy?
    You would be arrested the same day.
     
  3. perhaps - perhaps not. Depends on the country.

    R
     
  4. Somalia?
     
  5. SioL

    SioL Guest

    With this bandwidth it covers aircraft bands, pretty much guarantees you to be
    arrested probably in 99% of countries.

    SioL
     
  6. John Barrett

    John Barrett Guest

    look at a product called the TNC-X -- 1200 baud packet modem -- with
    appropriate software on your PC to act as a gateway, you can do TCP/IP over
    packet.... the interface to the radio is audio, so just about any voice
    radio will work with an appropriate cable to hook up the earphone,
    microphone, and transmit switch.

    Keep the frequency up as high as possible... in fact, you can basically
    scrap the 18-100 mhz range, atmospheric conditions can make so you cannot
    talk 10km with 100 watts under some conditions. and at the lower
    frequencies, there is every chance your signal will go MUCH further due to
    those same atmospheric conditions.

    I also strongly suggest beam antennas at both ends, up as high as your local
    laws permit.

    TNC-X packet modem
    http://www.tnc-x.com/

    AGW Packet Engine
    http://www.elcom.gr/sv2agw/

    I hope you have an FCC license (or the equivalent in your area) because for
    100km range, you will have to use higher power than is allowed for
    unlicensed operation in most jurisdictions. If your purpose is
    non-commercial, get an amateur radio technician class license, which will
    allow you to operate in the 144-148mhz "2 meter" band.... 50-100 watts will
    cover 100km quite nicely with a couple of 3 or 4 element yagi antennas..
    Getting the technician class license is pretty simple... most countries have
    dropped all morse code requirements, so its just a test you have to take to
    get licensed..

    And finally -- for 100km, you could most likely get away with a couple of
    2.4ghz parabolic antennas and run 802.11b wifi, which takes no licensing,
    uses off the shelf hardware, and has much higher data rates than 1200 baud
    packet. The only issue is getting your wireless access point as close to the
    antenna as possible... in a weatherproof enclosure mounted on the antenna
    mast. There are linksys routers that have open source firmware, and there
    are plenty of very reliable hacked firmwares that have features
    specifically for setting up point to point links. You put the parabolic on
    one of the antenna ports, and a small omni antenna on the other for people
    around the antenna to access.
     
  7. John Barrett

    John Barrett Guest

    If he meant 18mhz bandwidth -- there is nothing out there except wifi off
    the shelf for that bandwidth -- and you wont be running that at 130mhz !!

    I've got some 900mhz gear that will do 24khz bandwidth and thats clunky
    enough !! You can get amateur television hardware that will do 6mhz bandwith
    on a 1.2ghz carrier pertty easily, but then you are stuck with some pretty
    intense work to modulate and demodulate the data at that rate -- whip out
    your DSPs, boys !!
     
  8. ok

    ok Guest

    We have a licence for a particular frquency in range specified. No
    chance of geting arrested we are doing it all by legal means. Thanks
    to people all for the answers. Looking for right solution. thanks
     

  9. Well it is not that hard, TV at 67MHz with 6 MHz bandwidth is normal.
    I have build some small VHF TV modulators in the old analog days, to
    display output of stuff on the screen around ch4.
    The problem is limiting the bandwidth....

    The other problem he has is line of sight.
    At 130MHz the TV broadcast transmitter is on a > 100 meter high tower, and
    radiating many kW, and 100km is at the edge of range really...
    Analog TV is good old AM, and FM carrier for the sound here.

    Bit egoistic approach to grab 18MHz just for your personal Ethernet and
    pollute the whole area with it.

    The correct approach for that distance, if wireless, is to hire an up/downlink
    from a statellite provider, that comes actually cheap.
    Maybe there is no satellite service like that where the OP is.
     
  10. Ah, I have 1200Bd packet over 27MHz, do you have any idea how long a 1 MB download
    takes?
    LOL
     
  11. Guest

    I think the OP meant a freq range of 130MHz-180MHz (left out the '0')

    Covers TV broadcast and stolen vehicle trackers worldwide. Should get
    the cops on his ass real quick.
     
  12. Eeyore

    Eeyore Guest

    Why didn't you say you were in Oman ?

    Your problem will be that all existing solutions will be based around other frequency bands.
    I can't imagine it being that easy.

    Graham
     
  13. John Barrett

    John Barrett Guest

    I was being facetious -- the best solution for high data rates at that
    distance is wifi over parabolics -- though he will problably need 50ft high
    towers or better to pull it off -- and they aint cheap !!

    a slow speed (1200 baud) it can be done easily at 144mhz with off the shelf
    hardware and a ham radio license (non-commecial only)
     
  14. John Barrett

    John Barrett Guest

    I know exactly how long it takes :)
     
  15. John Barrett

    John Barrett Guest

    can you confirm the frequency range and desired data rate ?? would help with
    specifing a solution :)
     
  16. 18 MHz @130 MHz bandwidth is easily done with spread
    spectrum. Lowers detectability and interference.

    Rene
     
  17. ok

    ok Guest

    range is 130MHz to 180MHz ...sorry for the stupid typo mistake
     
  18. Another homework problem?
     
  19. http://www.lpbinc.com/indexNET.htm would have the power.

    Frequencies will be a tad lower.


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  20. Sometimes it did not finish at all.... :)

    It is not simply 1200 bits / second, but the packets are send as a frame,
    sync pattern first, CRC is added, then the transmitter waits for a reply
    (ack or reject if received CRC was wrong, because of for example interference),
    and then and only then (if the band is free from other transmitters, some wait
    time the transmitter listens) the next packet is send again.
    Hours.
     
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