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seeking some advice/knowledge relating to RF communication

Discussion in 'Radio and Wireless' started by Cona, Oct 2, 2014.

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  1. Cona

    Cona

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    Oct 2, 2014
    Hello!
    I would like to ask a question regarding the abilities of RF communication.
    I am looking at making a little project/device that would be capable of sending a distress signal over a RF.
    The objective is to create a small device that has the ability to send a small piece of information (such as gps coordinates) to a recipient. The environment in which this device would be situated in is my major hurdle; which would be a state forest/land reserve.
    Would it be possible to to send the mentioned information over a relatively dense environment for 5-10km?
    or is it simply impossible given the following requirements..(I am not very experienced in RF technology)
    - The device would need to be small (handheld).
    - The device would need to be battery operated.
    - The device would also need to power a gps.

    Would something like this achieve this, they state that it has a 7-10km range, but the environmental factors would adversely affect this.
    SO if anyone has any other products that would match this form factor and exceed in range, please let me know.

    http://www.csgshop.com/product.php?id_product=86

    Regards,
    Connor
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    hi Connor
    welcome to Electronics Point :)

    that device would be 7 - 70 km under near line of sight condition and possible with a directional antenna ( a yagi)
    you would be limited to a low gain whip antenna and foliage absorption would be reasonably high ( very high if it was wet with rain etc)
    you may only get a couple of km at best

    You would also have to check with your local authorities ( I don't know what country you are in ??)
    to make sure that you can legally use it at that power level without a licence

    cheers
    Dave
     
  3. Cona

    Cona

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    Oct 2, 2014
    Thanks for the response and information, yes liaising with the relevant authorities is a must. But I must be able to produce a sound design to present. I am in Brisbane, Australia. Is anyone aware of any such transmitter that is compact, power efficient and has a strong broadcast? or additionally any information regarding how the range could be extended without sacrificing the scale of the device?

    Regards,
    Connor
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    EPIRB?
     
    davenn likes this.
  5. davenn

    davenn Moderator

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    Sep 5, 2009

    Yeah ... agreed and that was going to be my possible response at some stage


    Connor, do you realise there are already commercially available emergency locator beacons ?
    They transmit on 2 freq's ---- 121.5 and 243 MHz. There are a number of satellites that monitor these freq's
    and can triangulate a beacon's location to around 10 - 20 metres pretty much anywhere on the planet
    there's a zillion wwww sites about and selling them

    I remember many yrs ago back in NZ during the 1990's there was a great calamity down the road from home that the local rubbish site. Police, ambulance and fire service all converging on the dumpsite.

    Later found out some clown had disposed of a ELB and hadn't removed the battery before dumping it
    it switched itself on and caused a huge fuss

    cheers
    Dave
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    I notice there have been freq changes since I was working with them back in the 1990's

    406.025 MHz digital transmission seems to be the main one now

    the 121.5 and 243 MHz were analog transmitters
     
  7. Cona

    Cona

    3
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    Oct 2, 2014
    Yes I do, its actually on the 406MHz freq. This is my other option, In laymen terms I am striving for the most power efficient, accurate device with the smallest form factor; this device will not just be a safety device, it will also be used to track and record much more information; which will be utilised by sports people. (e.g heart rate monitor, gps progress tracker) the ELB system is secondary. I am merely investigating different methods of sending an SOS, and my research has shown that emitting an SOS on the 406 feq will most likely be my best bet.
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
    OK well that's a whole different ballgame. you are really going to struggle to get any significant distance
    in difficult terrain from a small portable system


    yes and for that you will have to use a commercial ELB transmitter ... you are not going to replicate one
     
  9. BobK

    BobK

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    Jan 5, 2010
    Maybe this is a stupid question, but is there reliable cellular service in the area?

    Bob
     
  10. Gryd3

    Gryd3

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    Jun 25, 2014
    Would need to be a high powered transmitter, or some strategic placed sensitive receivers.
    Would need to be on a freq that is clear and available to use without upsetting anyone on the wrong RF spectrum.
    Would need to transmit sparsely to conserve battery power...
    This does not sound like a project that can be built by a beginner, or even many moderate electronics enthusiasts. You need to be able to understand how different RF frequencies travel and propagate, as well as determining what output power is required for the given distances / environments you wish to use the product in.

    Buying a pre-made product sounds like the way to go, or modifying/adding to an existing product that may have the characteristics you require.
    BobK brings up a good point regarding cellular service. A simple SMS could relay the information you require.


    Existing products like this will be hard to compete against > http://www.findmespot.ca/en/
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    perhaps some drones with repeaters?
     
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