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turn cable connections into wireless internet Answered

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 =]


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.

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.

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...

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...

I should have also mentioned that the ZigBee, Nortic type (and similar) data transceivers do the modulating and demodulating for you...

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.

this sounds fun to experiment with =] thanks. so it does not need to be modulated, right?

Jeez, I don't about that... I imaging a TV signal needs some sort of modulation...but it would depend on the signal source. I know I recent bought an RF modulator for my TV recently (convert video games or DVD output to a cable input) for only $4 USD...

The other issues:

--The wideband transmitter itself. Then the receiver, which would then convert the signal back into a broadcast band...
--A TV signal is usually broken up into separate transmitted bands for audio, color, etc. Whether an RF modulator takes care of all that, I don't know...
--Transmitting a strong 6 MHz wide signal in the shortwave band is a sure way to have the the FCC or homeland security knocking on your front door...

You can certainly buy low-power UHF frequency video transmitters. Or build one. I've got a copy of Radio-Electronics mag, Feb 1986 sitting on my lap right now. The cover project is: Build This Wireless Video-Camera Link .

alright, i'll experiment with it. thanks for your help =]

is it hard/possible to build such thing that modulates and demodulates? hope it's not too complex

Well, you could just adapt off-the-shelf telephone modems (you won't be able to exceed their speed with your own circuits.)

From a diy perspective, it does get pretty complicated...

--A modulator could be a simple as using a common 555 timer to create a waveform. Maybe use an FET as a switch to turn the signal on and off.

--Demodulating is more complex. Try using a 567 tone decoder.

Modern modems also have fault detection. If you're planning an one-to-one RF version of cat5, maybe the network protocols will handle bad packets, etc. But that probably includes some hardware handshaking, and I don't know how that will translate. You might need to design your own protocol, too.

wow it is complicated! right now, making this thing is even beyond my knowledge...i think i should drop this project for now.
thank you all for the help =]

I don't see why you couldn't experiment with low-power transmitters.

It's just that his schematics reminded me a similar project I saw, once, on the internet (can't find the link). The author did not really know what he was doing, and his transmitter was generating a lot of interferences because of "harmonics" ... =o)

So what you're saying is that this possibly could work, just have a great potential to cause interference? This was actually inspired by the idea of transmitting music via the radio (AM). Thanks

So what you're saying is that this possibly could work, just have a great potential to cause interference?

It has great potential to cause interferences if you don't really know what you're doing ... =o)
Well, I was not trying to discourage you. I was trying to make you aware that if you don't really know what you're doing, this could lead to various problems ... :o/

This was actually inspired by the idea of transmitting music via the radio (AM). Thanks

Remains devices for audio transmission, walkie-talkie, baby surveillance, video signal transmission devices, etc, that could be hacked for your purpose of course.

Well the radio idea sounds like it wouldn't be very easy to do but if the connection is within line of sight then you could make two four reciever four laser stations to acts as aline based on the sound over laser beam instructable, however getting definite off/on might still be hard to do. alignment needn't be a problem, a cleverly placed mirror or use of a window at the right angle means upstairs/ downstairs could be done via outside. Wait you would need two stereo connections at each end to make it work for radio. that means four radios in total. But four remote control car senders/recievers each end could work making a rudimentary wifi connection, it would also be working at the same speed as the wiring does, you'd need sixteen transistors, 8 remote control car remotes and recievers (different frequencies) however the circuitry and soldering would be minimal.

sounds very very complicated (at least for me it is). but anyways thanks for the help =]

hey do you guys have any idea of hacking an ADSL? i came up with this project becuase i can't access the wireless. the ADSL has some cable connections and a wireless lan. i am no expert at this, but is there any way that i could open it up or do some computer configurations so to get the wireless lan going? thanks

. When you say "AM radio" do you mean 520 kHz–1,610 kHz? If so, that will severely limit your bandwidth.
. Even shortwave AM (2.3 MHz–26.1 MHz) will be limiting (you'll never come close to achieving the theoretical max with DIY equipment).

good point! i've never thought of that. If i transfer data via the AM radio, that means it's in kilohertz, but todays wireless is like some gigahertz