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.
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.