turn cable connections into wireless internet

hey everybody
i just got this idea of making a wireless internet using ADSL (from cable form to wireless). There should be some cat5 cable connections. There are 8 pins in a cable, 4 of them are used: 1 pair for transmit (+ and -) and another for receive (+ ad -). I haven't experiment with this yet, but by connecting a crystal to the adsl, like transmitting music using AM radio, and connect a receiver, like most cd players that have abilities to receive am radio (perhaps solder the 2 wires from the speaker), this probably should work? Connect the same things to the computer, like the images below shown. So 2 crystals and 2 radio receivers are needed. Also, there should be 2 different frequencies, one for transmit and another for receive.
Hope this would work. Any thoughts and comments are very welcome =]

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The use of radio frequencies is regulated by local and internationals authorities. If your emitter is not designed correctly, your system could use forbidden frequencies and/or interfere with other equipments (yours, those of your neighbors, and maybe even farther) and may cause various unexpected incidents. I know it's less interesting than doing it yourself, but I'd recommend the use of WIFI technologies instead.
I don't see why you couldn't experiment with low-power transmitters. But you'd need to modulate the signal for transmission (and demodulate to receive.) So modems would be needed--kind of points to the speed limitations of lower frequency RF.

If you want to build on existing tech, how about Packet Radio.
J50Nunlimited (author)  gmoon10 years ago
nice suggestion =] but building a packet radio system seems a bit troublesome to me
my goal for this project was to build a wireless internet using components lying around, not to buy the big things
btw what do you mean by modulate/demodulate? i thought the receiver radio already done that
Your internet connection (via the cat5 cable) is binary DC. This type of signal can only be transmitted/received with a direct connection. A directly-wired connection has characteristics that RF does not; most important, the 'state' of the line (high or low) can be constant and persistent (pull it high and it stays there...) A radio signal transmits data in pulses; a form of AC. By their nature, radios can only send/get signals that are constantly changing. They are, after all, waves. So a 'high' signal needs to be converted into a series of pulses (modulated), and those pulses needs to be held long enough for the receiver to lock on, and identify that incoming pulse (demodulate.) That's the modem's job. This is the speed limitation--the RF carrier wave may be fast, but the actual data being broadcast isn't. AM / FM / Short wave were designed for voice communication, and like your telephone can only move a narrow band of data. Modems try to do an 'end run' by transmitting multiple signals simultaneously--but there are inherent limitations.
J50Nunlimited (author)  gmoon9 years ago
hey i just discovered this new thing: Digital to Analog converter and Analog to Digital converter! so by using this, i could modulate and demodulate the internet signals, right? i don't know much about this yet. the other day i was surfing on Atmel's web page and found a device called ZigBee...802.15.4 for WPAN (wireless personal area networks). i am hoping it would nice to use for this project.
Oh, if you're using some of the modern transceivers (ZigBee, Nordic, etc.), sure you could get something going (I thought you were committed to a 'ghetto' AM approach.)

You'd still need to design some sort of protocol, but that's part of the fun, right? After all, if you wanted a plug-and-go solution, you would have chosen a standard wifi rig....

sparkfun.com has a nice wireless selection, with datasheets handy so you can compare specs. I've used the Liapac RF modules myself. They are pretty-low speed devices, but were just fine for my application...
J50Nunlimited (author)  gmoon9 years ago
Awesome! sparkfun.com has those tiny, and yet powerful transceivers! (although it's pretty expensive) i think i will just build one using Atmel's ZigBee chips...and it will take me a long time, since i don't have such knowledge. but it will be nice if i release an instructable on this- cheap and easy wireless internet!
i know that protocols are like monitors for data communication; it governs them. i've never heard of actually designing them. thus i need to use some sort of encryption...wow it's getting so complicated...
gmoon gmoon9 years ago
I should have also mentioned that the ZigBee, Nortic type (and similar) data transceivers do the modulating and demodulating for you...
J50Nunlimited (author)  gmoon9 years ago
does transferring video/image signals (composite video) over AM radio need to be modulated?
I sincerely doubt you could broadcast a TV signal in the AM band... Standard AM signal is transmitted in the 520 kHz -1,610 kHz range. Single stations are spaced at 10K intervals. A single NTSC TV station occupies a total bandwidth of 6 MHz. That's ~6 times the total frequency range of the entire AM band. US channels begin about at about 45MHz. There may NOT be a frequency limitation here, as some of the earliest TV stations were broadcast starting at 1600KHz (just above AM and into shortwave bands.) So in theory, it might work in shortwave.
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