Modulation project

[BayArea98]

Hello,

I'm helping someone building a project to demonstrate modulation concepts. It's just like the radio but using sound wave instead.

1. I want to generate a sound wave and encode some data onto it. (data wave)
2. Generate a carrier sound wave and modulate it using the data wave
3. Capture the modulated wave using maybe a microphone
4. Demodulate it to separate the data wave
5. Should be able to store the waves in digital format

So far, I've figured out what I may need but don't know where to get it.

1. Sound frequency generator with wide range of frequencies
2. Encoder: Is there a product that I can use to encode data onto a sound wave
3. Modulator: Use a frequency generated "carrier wave" and modulate it by encoded wave
4. Microphone
5. Demodulator:

I'll need the guidance to build this project. If you can direct to me URLs of exact DIY kits or products or software to buy that would be great too.

I see some products and software online but need an expert guidance so I don't waste money in buying wrong software or kits.

Appreciate the help.

 

[Ian Rogers]

Ye'old modems used data transfer in the sound spectrum... Also anyone who owned a computer pre- 90's and loaded files by cassette....

 

[audioguru]

1) Morse Code modulated sound with a long and a short tone duration.
2) Another old modulation method of sound used a high pitched tone for a "1" and a low pitched tone for a "0".
3) DTMF (telephone touch tones) uses different pairs of frequencies for modulation.

 

[crutschow]

1) Morse Code modulated sound with a long and a short tone duration.
......................

Radio Morse Code actually just turns the carrier on and off in response to the key (the first digital modulator). The tone you hear is generated by a local beat-frequency oscillator (BFO) in the receiver.

 

[audioguru]

Radio Morse Code actually just turns the carrier on and off in response to the key (the first digital modulator). The tone you hear is generated by a local beat-frequency oscillator (BFO) in the receiver.

Of course. I forgot about the BFO because I was never a HAM. I learned only SOS.

 

[unclejed613]

try one of the newer ham radio digital communication modes. PSK31 is the most common, and one of the easiest to explain (assuming this is probably a school project). or you could go with RTTY, which is frequency shift keying.

 

[RichTheDude]

I would say OOK (On Off Keying) or FSK (Frequency Shift Keying) would be the simplest.

You could do everything you wanted with software like Octave or Scilab (free clones of Matlab), a pair of PC speakers and a PC microphone.

You can load wav files, save them, and do the appropriate processing.

http://www.gnu.org/software/octave/doc/interpreter/Audio-Processing.html

 

[unclejed613]

I would say OOK (On Off Keying) or FSK (Frequency Shift Keying) would be the simplest.

OOK can be human readable (morse code) or machine readable (ASCII serial data)

RTTY is the best known use of FSK. there's actually software out there that can do "all of the above"... look up FLDIGI or MULTIPSK. these are usually fed from the computer sound card into a radio, but work just as well using speakers and microphones.

with all of the various digital communication modes, some are easy to identify by ear, some are difficult to tell apart. there are even ways of sending pictures and binary files using some of these communication modes. some are relatively simple, such as OOK and FSK, and some are very complex, such as MT63. another interesting one is called feldhell, which uses OOK to draw letters on a paper strip similar to the way a dot matrix printer operates... the modern computerized version doesn't use paper strips, but would be compatible with the original WWII equipment if you had an old feldhell machine (or built one)

 

[RichTheDude]

I have done a bit of slow scan, but not much else. I have a class A ham license .

I was under the impression he wanted to figure out how to modulate and demodulate signals. Octave would let him do that mathematically / algorithmically at audio with none of the hassle of hardware. Most people have microphones and speakers to hand.

Depends how much he wants to learn I guess and whether he needs to just demonstrate it can be done.