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PhoneJacker

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CodeMachine

New Member
Hey guys,

I'm CodeMachine, I'm known in a few places. I've recently gotten the urge to get into electrical engineering and circuit engineering (I'm a teenager in high school, I took a quick class that lasted about a week or two in Physical science), but we only learned the basics. I do learn quickly, example: we only learned how to complete a circuit; battery, wire, bulb, switch, etc.. And a month ago or so I made a skeleton of a homemade alarm system for my bedroom.

I had this idea which would be awesome but I don't know where to begin in engineering, no one really has any good books (even though books don't help me a lot), and no one really can teach me the way I learn.

OKAY, the idea: Battery, dial, transmitter, speaker, switch.. I think that's it. The battery goes to the switch, which goes to the dial. The dial adjusts the frequency that goes to the transmitter, which goes to the speakers for any feedback. Then the circuit repeats. You adjust the dial to the right frequency the phone-line is using so you can pick up on the conversation, let's say. I just read a thread post that said "It uses the same frequency as a microwave, so major interference". That's kinda what I'm looking for, and everything that's being picked up on that particular frequency will be played through the speaker. Ya get it?

If you can't help, at least give me some places to go to begin my little adventure. If you can really help me, please post. If you guys help, I might stay for an extended period to learn some more from you guys lol. Thank you very much,

CodeMachine
 

audioguru

Well-Known Member
Most Helpful Member
I guess you are talking about a cell-phone, not an old wired phone.
When you study cell phones then you will learn that they use many frequencies in modern countries and some keep changing their frequency during a call (spread spectrum).
You will learn that they have digital modulation then will sound like buzzing on a radio if the radio can receive and lock into the frequencies of their signal.

About 25 years ago you could have used a wireless home phone to hear what your neighbour is saying on their wireless home phone.
 

Torben

Well-Known Member
Many wireless home phones do use the same band as a microwave oven (2.4GHz) although some use other frequencies: What are the cordless phone frequencies?

It sounds like you want to build a device to listen in on cordless phone conversations. With older analog phones you can do this with a police scanner (although you might have a hard time getting your hands on one legally, if you're in North America). Digital or spread-spectrum phones are much tougher to eavesdrop on as the signals are either encoded, or bounce around the spectrum, or both.

I'm afraid there is a lot more to a project like this than what you've outlined. Most of the complexity (at least, as far as analog phones go) is in what you've called the 'transmitter', although that should be called the 'receiver' (a transmitter sends information; a receiver. . .er. . .receives it).

I'd recommend picking up a copy of the ARRL Handbook (Google it and/or look for a local ham radio shop and/or visit a local library) to get acquainted with the basics of radio communication. You'll need some serious chops to build anything which will reliably work at 2.4GHz or higher, though--so start smaller and see if you can build a receiver to pick up regular radio signals first. There are lots of projects to practice on in the ARRL Handbook and on the net (and in other books and references).

Anyway, you have good enthusiasm. A receive like what you've described isn't a simple task but if you cover the basics first you can get there in the end.


Torben
 

Mr RB

Well-Known Member
Almost every cordless household phone these days is digital, channel changing and encoded. They have to be because the main market is city people.

It was only back in the 80's people would complain that their handheld phone could hear the neighbours talking and even by 1990 those old analog home phones were phased out.

Since you can buy cordless phones for $50 or so most families just upgrade them every few years when the handheld's batteries die. There won't be many analog ones left in use...
 
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