Listening In on Hidden Signals

Listening In on Hidden Signals was Originally Posted on July 15, 2013 by lavarock

A Reuters report today states that a couple of researchers have found a way to hack a cellphone repeater to listen in on other peoples cell calls. This is not surprising to me or other people in telecommunications.

Much of our telecommunications have been public all along. When people sent smoke signals, they might have been encrypted (using some unknown language) but the fact the message was being sent was obvious.

Decades ago people would get a baby monitor or cordless phone and neighbors could listen in with just a police scanner. In the case of early mobile telephone calls, you could twist your UHF TV tuner up near channel 79-82 and listen in. TVs then began having digital or click tuners and finally that part of the spectrum was taken out of TV service.

Certain Ham radios can listen in on many services like CB and police calls, etc.

Many decades ago I listened to overseas telephone calls directly from a satellite. The channel was a few channels away from the HBO transponder that every cable company and some home enthusiasts had easy access to.

Remember the beeper? Many of us carried them. You would dial a telephone number, enter some info and the beeper would go off with the message. Did you ever wonder how it worked? Well, there were a few beeper frequencies in a town and like a radio station, the company would send message after message on that frequency/channel. Each beeper in that company’s service listened to all the messages. Your beeper had a code (like a phone number) and would see every message sent. When it noticed a message with your number in the header, it would display the message. So if you could get to the code (or knew a place to cut a track), you could see every message that company was sending out.

With telephone service from the phone company (traditional plain old telephone service), a telephone lineman could sit up on a pole and listen to your calls. (Years later the NSA could have just listened from the phone company offices). With just a dollars worth of parts from Radio Shack, you could listen undetected to pretty much any home phone in the U.S.

Some radio and TV stations use a hidden signal to communicate with an employee at a remote site. This SCA signal can be audio or perhaps control or data reporting. A simple SCA adapter may allow you to hear the DJ in a studio talking with people on the telephone and off the air. That signal might be listenable anywhere the main broadcast signal is heard. http://en.wikipedia.org/wiki/Subsidiary_Communications_Authority

A system called a simplex or a phantom circuit allows use of a set of wires to carry a hidden or extra service. If you are into electronics, watch this: http://www.youtube.com/watch?v=H4NDVkjT9mg

In old movies, you may see a blinking square in the upper corner of the picture, just before the movie reel needed to be changed to the next reel. Network soap operas also used a similar item just before the characters froze on screen and the dramatic music started. A commercial soon followed. http://en.wikipedia.org/wiki/Cue_mark

Decades ago my uncle Ralph would point his Ham antenna towards space. He heard signals and voices from the distance. No, not alien voices, other Ham Radio operators. These Hams were not out in space, but were talking to each other via a natural radio reflector. You call it the moon. They called it fascinating. The term used to specify communications from Earth to Moon to Earth was EME. Although not a perfect reflector, the moon does allow radio signals to bounce off it, assuming you have enough power and big enough antenna. In a recent “Big Bang Theory” show the guys shine a laser into space and reflect it off a reflector left on the moon. http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment

These are but a few of the hidden signals I know about. They may spark interest in you, or perhaps not. Still, the next time you watch an old movie, that little blinking indicator is bound to catch your attention.