Nuts and Volts - December 2008

information on the switch-over is there, as well.

When the analog to digital switch-over occurs, your local stations will move to different channels, most likely from VHF to UHF. If you don’t know how to find the new channel, you can go to the FCC’s website ( www.transmitter.com/FCC98315/ chanplan.html) and get details there. One quick comment on antennas. If your rabbit ears get both VHF channels (2-13) and UHF channels ( 14-59), you will be okay. Same with an outdoor or attic combo VHF/ UHF antenna. Remember, higher frequencies travel shorter distances than lower frequencies for the same power. So, your stations new UHF signals could be lower in level with the new digital TV. A higher gain antenna will make up the difference.

With digital signals, there is no gradual weakening as indicated by “snow.” What you will get is a pixilated screen and then nothing if you are out of range.

■ FIGURE 1. This

GSM/GPRS M2M cell phone modules by Telit Wireless Solutions is only 1.7 x 1.7 inches square and operates in the standard 850/900/1,800/1,900

MHz cell phone bands. It can send short text messages or audio. This model has a built-in GPS receiver so it can report its location to the caller.

M2M ON THE RISE

What the devil is M2M, you ask? It stands for machine-to-machine. It is a growing technology that extends the use of a cell phone system to other than personal human to human voice and text communications. Instead, it implements communications between machines — machines talking to other machines or humans talking to machines. Sounds a bit eery at first but as it turns out, it is an amazing additional use of the large and very expensive cell phone infrastructure made up of over 260,000 base stations in the US alone. Here’s how M2M works. It is a form of wireless telemetry and control. Telemetry is the old term that means measurement at a distance — usually by wireless. Suppose you want to watch the temperature of a pipeline miles away from you or even across the country. You install a temperature sensor on the pipe and send the electrical signal to a cell phone. The cell phone is basically just the radio without the keyboard, display, speaker,

and microphone. It sends the digital version of the temperature over the cellular network to your phone or computer.

Suppose you want to control the liquid level in a remote tank. You could monitor the level with a sensor, then use that indication to turn a pump on or off to refill the tank when necessary. Could all be miles or a continent away.

M2M is the ultimate long range remote control. As long as you can get through a cellular network, you can monitor or control anything from any place at anytime. M2M has been around a few years and growing silently. Tiny cellular radios in modular form are cheap and widely available to enable almost any conceivable remote monitor or control function at a very reasonable price.

Vending machine companies use M2M to alert them that a machine needs refilling or maintenance. Trucking companies routinely use it to track their trucks and payloads. Companies attach an M2M transceiver on a high value asset like a bulldozer or large crane and monitor its presence or condition by a simple phone call. You can even put a video camera on one of the transceivers and keep an eye on your home while you are on vacation. Just call in and take a look at the current video conditions. Figure 1 shows a typical M2M cell phone module.

M2M is an impressive extension of the cellular system. With cell phone saturation nearing 50% of the

world population of just over 6. 5 billion folks, where does one go for growth? The answer is M2M. Some companies have estimated that there could be between 50 or 60 billion devices, machines, or things that ought to be monitored, tracked, or controlled. M2M is cheap and easy, so look for more of this “invisible” technology.

WHITE SPACES IN YOUR FUTURE

Another hot topic these days in wireless is “white space.” This is the term for those TV channels that will become vacant during the switch-over from analog to digital or those TV channels essentially unused or unassigned. With spectrum so limited and expensive, many are wondering why all that precious TV spectrum will go unused. Why not put it to work in cellular or other forms of wireless like high speed Internet connections or wireless networks? Most of it is in the highly valued VHF spectrum where signals travel far, penetrate walls, and allow many new useful services to be implemented.

By using smart technology, a radio will be able to monitor the spectrum for potential interference before transmitting and then decide not to transmit or to change frequencies.