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Low cost Radio tranceiver Range :5Km Baud Rate : 19200-115200baud

Discussion in 'Hobby Electronics' started by Guest, Jul 13, 2004.

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  1. Guest

    Guest Guest

    I'm looking for "Low Cost" radio tranceiver with 5Km range and full-dublex
    19200-115200 baud rate. Would you suggest one?
     
  2. Mark Little

    Mark Little Guest

    Could you tell us what you want it for?

    If low cost is a prime consideration, you may be better off looking at half
    duplex systems. If you don't especially want a serial port connection, you
    may like to consider 2.4GHz Wireless LAN cards with a good antenna system.

    Mark
     
  3. Guest

    Guest Guest

    What about the range of 5Km? Do you thik wireless LAN (802.11) would reach
    that far?
     
  4. Mark Little

    Mark Little Guest

  5. atec

    atec Guest

    with the right rx/tx aerials you can expect considerably more , and
    quite cheaply
     
  6. A full duplex system requires two separate radio links, one for each
    direction. To avoid the problem with duplex filters, use two complete
    separate unidirectional radio links operating at different frequency
    bands.

    A 5 km range is easy, if you have a _guaranteed_ line of sight, but if
    not, it becomes quite tricky to get a decent reliability, requiring a
    lot of power (several watts), special modulation and coding systems to
    avoid selective fading etc.

    Then you have to consider in which countries this system should be
    operated and check separately for each country which frequency bands
    can be used for this kind of operation. Remember, you need two
    separate bands, if you insist on full-duplex operation.

    It would be easiest if some license exempt bands could be used, but
    these are usually limited to 10-100 mW, which would not be sufficient
    for reliable 5 km non-light of sight paths at those speeds. Also note
    that there are usually a lot of all kinds of other activities on
    license exempt bands that could block your link at much shorter
    distances, thus, you may need some frequency hopping or spread
    spectrum system to avoid the other users.

    For reliable systems, most likely a licensed radio system would have
    to be used, with type accepted devices and separate licenses for each
    installed transmitter. Depending on your definition of "Low Cost" this
    may or may not be acceptable :).

    Paul
     
  7. On Tue, 13 Jul 2004 20:20:45 +1000, atec

    While a WLAN link can be longer than 5 km, you need quite high towers
    to have a clean line of sight path between the stations, with
    preferably no obstacles within the first Fresnel zone :).

    In most countries the WLAN is limited to 100 mW ERP (+20 dBm) and when
    the path loss for 5 km and 2450 MHz is 114 dB, the received power with
    an omnidirectional antenna would be -94 dBm. After the feeder losses
    at the receiving end the power level entering the WLAN card can be
    calculated. Compare this figure to the nominal sensitivity of the WLAN
    card at various speeds and you know how much receiver antenna gain you
    are going to need. This calculation assumes a clean path with
    unobstructed Fresnel zone.

    You must also consider the local noise level near the receiver from
    other sources.

    Paul
     
  8. Guest

    Guest Guest

    One of the unit in my implementation will be mobile and therefore wireless
    LAN seems to be out of question (no tower, no directional antenna). Any
    other recommendation?
     
  9. Mark Little

    Mark Little Guest

    COuld you define "low cost"? - it such a relative term.

    Mark
     
  10. Guest

    Guest Guest

    < US$300
     
  11. Mark Little

    Mark Little Guest

    Have a look at this unit. It is US$269. It will have the same problems as
    the Wireless LAN as it operates in the 2.4GHz band as well.
    http://www.microdaq.com/wireless/aerocomm/index.php

    If this is for import to Australia, you will need to add freight and GST
    (depending on application). You may get a tax reduction as an export from
    the country of origin.

    If you are looking for a unit with a that will handle 5km all terrain, you
    will need to up your budget. Using something outside of bands like the
    2.4GHZ band, you may require a licence which will add to your costs.
     
  12. GSM? Cellular technology is cheap enough these days.
     
  13. Guest

    Guest Guest

    GSM device itself is not expensive but call charges are not.
     
  14. Try wifi with a decent antenna.

    A modified satellite dish gives 29dBi which will easily do 5 km, but an
    omnidirectional waveguide may work too.
    http://members.iinet.net.au/~clark/FreeNet/Satenna/

    Approximate wifi distances for various antenna types are at the bottom of
    this page:
    http://members.iinet.net.au/~clark/FreeNet/antennas.htm



    gtoomey
    www.ausinvestor.info  Australian Investor Forum
     
  15. Unbeliever

    Unbeliever Guest

    GPRS, then?
    < $200 US. Call charges negligible for smallish amounts of data in
    Australia.

    Alf.
     
  16. Completely unrealistic with those requirements.

    Drop the full duplex and data requirements and provide at least nearly
    line of sight paths (with the other station up in a high tower or
    balloon) may make the situation more realistic.

    Paul
     
  17. Mjolinor

    Mjolinor Guest

    Hmm, sounds like an EER application to me.
     
  18. Zak

    Zak Guest

    In the Netherlands you can get a rate of Eur 1.5 / megabyte for GPRS.
    For sending and receiving, so for GSM-to-GSM cost you have to double it.
    But if the amount of data is limited this is very acceptable.


    Thomas
     
  19. The good thing with the original 1200 bps half duplex audio FSK system
    is that it works with practically any unmodified radio telephone with
    a microphone and headphone connector, thus simplifying any type
    acceptance issues.

    The 27 MHz Citizens Band might be an alternative to reach the 5 km
    distance, provided that data transmission is allowed on the CB
    frequencies in a particular country. Of course, the 1k2 half duplex
    throughput is "slightly" below the 19k2.. 115k2 full duplex throughput
    expected :).

    Paul
     
  20. Cody

    Cody Guest

    With that kind of size, it's difficult to fit into a model plane...

    Kelvin
     
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