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.

 

Oh and for now i am ignoring legal issues of restricted freq .

The rest of us are not ignoring these issues. Please review: http://forum.allaboutcircuits.com/announcement.php?f=6&a=3

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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.

 

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.

 

An audio bandwidth of only 3.4kHz is very poor for voice communication. Like a lousy old AM radio.

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.

 

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.

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.

 

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)

 

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