digital walkie talkie

Discussion in 'The Projects Forum' started by jinalkothari, Sep 13, 2008.

  1. jinalkothari

    Thread Starter New Member

    Sep 13, 2008
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    I am very much a newbie to electronics, so I hope some one can help me out here. I want to design and implement a full duplex , digital walky talky. The hardest thing for me in the project is the data transfer between two devices. I wish to have a range of atleast 1-2 km, but i don't know which frequency to use or what modulation to use ( I am adamant about the data being digital and not analogue ) . I would obviously prefer an ic for the modulation. the data input to the modulator should preferably be parallel(8 bit) , but if not feasible i don't mind serial either. I am also not quite sure how do i actually put the output from the modulator 'on air' .

    Oh and for now i am ignoring legal issues of restricted freq . and i am not very sure of the data rate but the minimum i need is that enough for decent voice transmision ( i hope you understand my non technical lingo)

    I also think that it is not required for the ic to handle any protocols , as i have a microcontroller which would handle everything.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    The rest of us are not ignoring these issues. Please review: http://forum.allaboutcircuits.com/announcement.php?f=6&a=3
    That having been said, voice transmission only requires about 3.4 kHz bandwidth. If your ADC sampling rate is 8 kHz or better, and nobody is mumbling, you will have intelligible communication.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    An audio bandwidth of only 3.4kHz is very poor for voice communication. Like a lousy old AM radio.
    All letters must have a name because they are niot clear. Say Bravo instead of "B". Say Charlie instead of "C". B or C sounds like 'ee.

    Most consonants are at 14kHz and higher. S, F and a few other sounds are much highrer than only 3.4khz. The 15khz bandwidth of FM radio and TV produces the high frequencies properly.

    Telephones and communications have used a narrow bandwidth to save spectrum space.
    Imagine what it is like to be deaf to high frequencies and hear only vowels.
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
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    It's good enough for the military, and for the phone company. If you need a hi-fi system for your paintball team or your hunting buddies, then design accordingly.
     
  5. jinalkothari

    Thread Starter New Member

    Sep 13, 2008
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    that's not what i had meant, i meant i am only designing it for now. When i actually implement it , of course i would have to keep the laws in mind.
     
  6. jinalkothari

    Thread Starter New Member

    Sep 13, 2008
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    I am planning to modulate DIGITAL audio data. Can anybody suggest an ic please ? ( make rational assumtions when answering, because I might not have been very clear or specific about the problem statement)
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Modulating digital is modulating digital. It won't care if the bits are voice or pictures or text or whatever.

    Perhaps this is the kind of thing you are looking for: http://www.ti.com/lit/gpn/cc1020
     
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