Windows XP / Networking

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How can I extend the life of my computer's battery?

A radio transmitter consumes electric power as it sends and receives radio signals, so the battery in a portable computer with a wireless adapter will run down much faster than the same computer without the adapter. Fortunately, there are a few things you can do to keep the power drain down to an absolute minimum.

First, turn off or disconnect the adapter when you are not using it. If you are on an airplane or a train, or anywhere else where you are outside the range of a wireless signal, or if you are using the computer for some purpose that does not require network access, remove the PC Card adapter from its socket or unplug the USB cable. If your computer has an internal wireless adapter, turn it off.

This is good advice for any plug-in device on a PC Card. If you are not using it, remove it. Modems, Ethernet adapters, and storage cards all consume power any time they are plugged into the computer, so your battery will keep going longer if the socket is empty.

When you use your wireless network adapter, you can reduce power consumption by using the Power Saving Protocol that is part of the 802.11 specification. Someplace in the adapter's configuration utility, there is a set of power management options that can instruct the adapter to enter a power saving mode:

• Constantly Awake Mode (CAM) consumes the most power and provides the fastest response. In CAM mode, the adapter is on all the time. It receives all incoming messages as soon as the access point gets them.
• Power Saving Protocol (PSP) mode consumes less power, but it also provides slower response. In PSP mode, the adapter instructs the access point to hold messages for this network node in a buffer, and it enters a low-power sleep mode. At regular time intervals (several times each minute), the adapter wakes up and polls the access point for messages. Because there is a delay between the time the access point receives each message and the time it sends the message on to the sleeping adapter, data and messages will take longer to move through the network.

I have heard that radio signals from cellular phones might be dangerous. What about Wi-Fi?

Some people believe the jury is still out on the safety of cellular telephones. Others are convinced that they're a serious health threat. Scientists and engineers have performed studies and published papers that claim to prove that extended use of a cell phone can-or can't possibly-cause cancer, make milk go sour, or have some other terrible effect. Human exposure to electromagnetic fields at the frequencies used by cell phones and wireless network adapters is within the levels that most organizations and regulatory agencies that have studied the matter consider safe. The dissenters believe that those levels are too high.

Even if you think cell phones are potentially dangerous, it is likely that the radios in wireless adapters are safer, for several reasons. First, when a cellular telephone is transmitting, it is usually just an inch or two from the user's brain, but a wireless adapter is probably a foot or more away (even though they are called laptops, most people use them on a table rather than on their laps). The effect of nonionizing radiation (a fancy name for radio waves) decreases at a rate equal to the square of the distance, so a transmitter located two inches from your head will have about 36 times more effect on your body than a radio located a foot away, assuming that both radio signals are equally strong at the antenna.

Second, the radio in a cell phone is 20 times more powerful than a radio in a wireless adapter (0.60 watts versus 0.03 watts), so the intensity of the signal is more than 700 times stronger.

Finally, the effect of radio frequency radiation on organic matter is cumulative-the longer the body is exposed to radiation, the greater the effect. Most cell phones transmit a continuous stream of packets as long as the phone conversation is going on, but wireless LANs are bursty services that are only active when they are actually transmitting data. The total amount of transmission time for a wireless adapter is just a fraction of the time that a cell phone is active.

Therefore, the total amount of radiation your body receives from a wireless network adapter is just a tiny fraction of the amount you receive from a cell phone. There are plenty of other, more serious, threats to your health and safety.