300' range TX and RX setup. What type is best??

Discussion in 'The Projects Forum' started by tonga, Aug 8, 2010.

  1. tonga

    Thread Starter New Member

    Aug 8, 2010
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    Hi-
    What would be the best method to transmit from a small portable transmitter to several SMALL lightweight receivers that would not be more than a maximum of about 200'-300' away at any time? FM,AM,SW,IR,RF? What is the maximum range the FCC lets you transmit in any of those spectrums without a special license or permit? Ideally, I am looking to have the TX and RX's be able to select from 3 or 4 set frequencies that you could select with a simple switch (not have to manually tune in some freq). The other major consideration is that the receiver be very lightweight, preferably able to power a miniature speaker while using only button type or watch type batteries.

    I'm not sure if it is even possible to use such small batteries, but that aspect is probably the most critical of all.

    What do you all think? Doable or not? :confused:

    Thanks
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    First, you want to familiarize yourself with this:

    http://www.access.gpo.gov/nara/cfr/waisidx_08/47cfr15_08.html

    Then you need to check out commercially available modules, such as these:

    http://www.linxtechnologies.com/

    I suggest that rather than use separate frequencies for each device, you identify each device with a code. It is much like garage door openers and key fobs. When you use your garage door opener (or key fob) every other door in the neighborhood doesn't open, but they are all or mostly all on the same frequency.

    John
     
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    The FCC goes on maximum effective radiated power and the allowance varies by frequency band.

    Antenna gain is taken into consideration as well so where you may get by with a 1W transmitter into a unity gain antenna you'd be limited to less power were the antenna directional and possessed gain.
     
  4. gootee

    Senior Member

    Apr 24, 2007
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    Can you give us a clearer idea of what you are trying to do? What is this going to be used for?
     
  5. BMorse

    Senior Member

    Sep 26, 2009
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  6. tonga

    Thread Starter New Member

    Aug 8, 2010
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    I should have been a little more specific. I am looking for voice communications in this setup. I coach youth baseball and would like to be able to communicate with all the players without having to yell to the outfielders etc. The receivers would therefore have to be small and light enough to clip onto the bill of the hat and have a tiny speaker (like being able to hear your cellphone on loudspeaker mode) so they could all hear what I'm saying. 3 or 4 'set' freqs in case there was interference on one freq.

    What would be the best medium for this application? FM tx and tune in on FM rx? Or some other type band?
    Thx
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    1) Why not just use cell phones or whatever color berry is now popular?
    2) If that fails, try an off the shelf walkie talkie.
    3) I think to design, build and license something like you describe is a bit too complex for someone with little experience in electronics.
    4) Do league rules allow such wireless communications? Why not let the kids just have fun while learning the game.

    John
     
  8. bradstormer

    Member

    Aug 6, 2010
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    the first two of your list (AM,FM) are just types of modulation and as such dont really affect distances. IR stands for infra red and would be far too directional for your requirements. RF just stands for radio frequency. SW is a part of the High Frequency band of the radio spectrum.
    the difference between FM and AM is the sound quality (AM commonly used by phones, FM used by music radio stations), but for your application the sound quality is not really important.
    do you intend on making or buying a solution?
    maybe if you hacked a short range FM transmitter (like those that connect an MP3 player wirelessly to your car radio) and tuned in some cheap FM receivers available from most shops (just regular personal radios that you tune to a station). should be relatively easy...
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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  10. bradstormer

    Member

    Aug 6, 2010
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    those seem ideal!
    what kind of application to you intend to use them in?
     
    Last edited: Aug 12, 2010
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I haven't a clue, at that price they seemed like something to just buy and have around. I haven't taken one apart yet but I'd bet good money they're easily tuneable. They don't appear to be potted in any way, looks like a sharp X-Acto knife would open them right up to find a slug tuned or air stretchable coil.
     
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