The Wireless Age

We are currently cruising at FL360 in a Falcon 900 over the South Central United States. Having accompanied our aircraft through a major refurbishment at a well-respected maintenance repair organization (MRO), we are testing and inspecting the new equipment and furnishings back in the cabin. It has, so far, been a very comfortable and convenient trip due to the various functions that can be accessed through wireless connections. First, I needed to check my email, so I activated my laptop and noticed that it logged onto the aircraft Wi-Fi requiring me to open my web browser to retrieve my messages.

During that time, I decided it would be nice to listen to some soothing music, so I then picked up a remote control and selected the XM Radio. I was able to find a channel with some suitable tunes. About that time my email appeared and when I read the first note, it required a followup conversation, so I pulled one of the cordless cabin telephones from its charging cradle and proceeded to place a call to our primary maintenance base to discuss the topic of the email. About that time, another passenger asked for the cabin remote control to turn on one of the DVD players. Before I gave it up, I selected the XM Radio off the cabin speakers and donned a wireless headset and selected the XM Radio to the audio input for the headphones. My co-passenger then took control of the Airshow by selecting CNN with the wireless mouse.

This is the age of Wireless, Wi-Fi, cordless, infrared (IR), and radio frequency (RF) controls.

These expressions are frequently used to describe an operating concept and are not always associated with their specific operating method.

In 1898 at an exhibition at Madison Square Garden, Nikola Tesla demonstrated a small boat which could apparently obey commands from the audience but was, in fact, controlled by Tesla interpreting the verbal requests and sending appropriate frequencies to tuned circuits in the boat. He was granted a U.S. patent on this invention on Nov. 8, 1898.

The term “Wi-Fi” suggests “Wireless Fidelity,” compared with the long-established audio recording term “High Fidelity” or “Hi-Fi.” “Wireless Fidelity” has often been used in an informal way, even by the Wi-Fi Alliance itself, but officially the term does not mean anything.

First used commercially in August 1999, “Wi-Fi” was coined by a brand consulting firm called Interbrand Corp. that had been contracted to determine a name that was a little catchier than “IEEE 802.11b Direct Sequence.” Interbrand invented “Wi-Fi” as simply a play-on-words with “Hi-Fi.”

Wi-Fi allows local area networks (LANs) to be deployed without wires for external devices, typically reducing the costs and increasing flexibility of network deployment and expansion. Spaces where cables cannot be run can host wireless LANs.

Wireless network adapters are now built into most laptops. Wi-Fi has become widespread in aviation infrastructures.

Wi-Fi standards
Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.

The 802.11 family includes over-the-air modulation techniques that use the same protocol. The most popular are those defined by the 802.11b and 802.11g and are amendments to the original standard. The first wireless networking standard was 802.11-1997, but 802.11b was the first widely accepted one, followed by 802.11g and 802.11n. Security was originally purposefully weak due to export requirements of some governments and was later enhanced via the 802.11i amendment after governmental and legislative changes. Standard 802.11n is a new multi-streaming modulation technique while 802.11b and 802.11g use the 2.4 GHz ISM band, operating in the United States under Part 15 of the U.S. Federal Communications Commission (FCC) rules and regulations. Because of this choice of frequency band, 802.11b and 802.11g equipment may occasionally suffer interference from microwave ovens, cordless telephones, and Bluetooth devices.
The 5 GHz U-NII band is used in conjunction with 802.11a, which, for much of the world, offers at least 19 nonoverlapping channels rather than the three offered in the 2.4 GHz ISM frequency band.

However, propagation around objects such as bulkheads and furnishings tends to be better at higher frequencies. These higher frequencies tend to scatter more, which helps them get around objects, whereas penetration is better with lower frequencies. You may get better or worse performance with higher or lower frequencies (channels) depending on environment, as Wi-Fi tends to reflect from objects rather than go through them.

Another factor in performance is absorption by water and moisture. A frequency of 2.4 GHz is very close to the oxygen-hydrogen bond frequency which means the chemical composition of water may create a significant absorption of the 2.4 GHz Wi-Fi signals. Higher and lower frequencies have less of a problem.

The segment of the radio frequency spectrum used varies between countries. In the United States, 802.11a and 802.11g devices may be operated without a license, as stated in Part 15 of the FCC rules and regulations. Frequencies used by channels one through six (802.11b) fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC rules and regulations, allowing increased power output but not commercial content or encryption.

Installation procedures
Aircraft Wi-Fi installations are very much concerned with electromagnetic induction possibilities associated with a wireless cabin. The FAA requires high power wireless routers to be certified prior to installation. The current interpretation of “high power” is anything greater than 25 milli-watts.

Many remotes for electronic devices use a near infrared diode to emit a beam of light that reaches the device. A 940 nm wavelength LED is typical. This infrared light is invisible to the human eye but is picked up by sensors on the receiving device. Video cameras see the diode as if it produces visible purple light.

With a single channel (single-function, one-button) remote control, the presence of a carrier signal can be used to trigger a function. For multi-channel (normal multi-function) remote controls, more sophisticated procedures are necessary and utilize digital communication. One can often hear the signals being modulated on the infrared carrier by operating a remote control in very close proximity to an AM radio not tuned to a station.

Since infrared (IR) remote controls use light, they require line of sight to operate the destination device. The signal can, however, be reflected by mirrors, just like any other light source, and may be susceptible to cancellation by a higher intensity beam. In aircraft, proper location of a photo cell is critical as streaming sunlight may interfere with functionality.

If operation is required where no line of sight is possible, as when controlling equipment in a concealed location, an IR extender may be employed. Most IR extenders have an IR receiver, picking up the IR signal and relaying it via radio waves to the remote part incorporating an appropriate receiver and infrared transmitter mimicking the original IR control.

Infrared receivers also tend to have a more or less limited operating angle, which mainly depends on the optical characteristics of the phototransistor. However, it’s easy to increase the operating angle using a matte transparent object in front of the receiver.

Existing infrared remote controls are frequently used to control personal computer (PC) operations. Almost any application that supports shortcut keys can be controlled via IR remote controls. This is widely used with multimedia applications for PC-based audio and video systems. Connections are most often made via serial or USB port. The widely used Collins Airshow in-flight display is one example of a system capable of using this technology.

Well, we have almost completed our journey. The Airshow is displaying time to destination at 20 minutes but, of course, my job is not yet finished.

I wonder if it is feasible to build a wireless remote control lavatory service cart.

What a concept!

Jim Sparks has been in aviation for 30 years and is a licensed A&P. His career began in general aviation as a mechanic, electrician, and avionics technician. In addition to extensive hands on, he created and delivered educational programs for several training organizations and served as a technical representative for a manufacturer of business jets. Currently when not writing for AMT, he is the manager of aviation maintenance for a private company with a fleet including light single engine aircraft, helicopters, and several types of business jets.