Reach Out and Touch Someone
By Jim Sparks
Making a telephone call has been for years a very simple task. With new technology, telephone lines now provide much more than the ability to say hello to Aunt Edna on a Sunday evening. In fact, in today"s fast-paced business world, telephone access is a necessity.
It used to be that travel via ship, rail, car, or aircraft provided a rest from the stresses of the business world. But, as time is money, the communications industry began providing means of "staying in touch," even though the world might be passing by at a high rate of speed.
Commercial airlines, along with many business aircraft, are equipped with telephone systems that not only provide voice communication, but allow the transfer of electronic media through data links. When considering that many of today"s aircraft can travel thousands of miles at speeds approaching — and in some cases — exceeding that of sound, it is rather unrealistic to think of an airborne telephone system on the order of the pay phone down at the corner. Radio waves now take the place of wires and poles.
While aircraft technicians are responsible for safe and timely flights, now they also are required to ensure that passengers can conduct business whenever they need to.
Telephone communications from aircraft are categorized as either "Air to Ground" or "Air to Air." In either case, specialized technology and equipment are required. Just like with home long distance service, the aviation telecommunications market now has numerous players, and industry giants AT&T and GTE each has a significant share.
Flitefone,™ or now Claircom,™ are the AT&T systems with over 150 ground stations that provide coverage over the continental United States, Alaska, Hawaii, the Caribbean, and Canada. MagnaStar™ is the system used by GTE and has over 100 ground stations with similar coverage areas. Earth-orbiting satellites provide for "Air to Air" communications. Commonly referred to as "SATCOM," these satellites are connected to ground stations and can presently deliver communications coverage over about 85 percent of the planet with a new system on the horizon promising close to 100 percent coverage.
In the "Air to Ground" arena, the MagnaStar and Flitefone systems are functionally similar though the components are not interchangeable. In both systems, an Airborne Radio Telecommunications Unit (ARTU) provides the medium to connect the aircraft with the ground stations. The ARTU is both a receiver and a transmitter utilizing 290 channels. Frequency range during transmission is 894 to 896 MHz and the receive side is in the 849 to 851 MHz spectrum. The ten watts of transmitter power is quite adequate to provide contact with the vast array of ground stations. "Always Listening" is one of the features of the ARTU receiver that enables determinations of which ground station to use and when to hand off to another cell. It also offers tuner control and even power management along with encoding and decoding of both audio and digital signals, plus provides the protocol to interface with the ground network. An ARTU will also include Built-In Test (BIT) during power up and performs continuous system monitoring. Provisions are also made on the face of the ARTU to connect a patch cable to a laptop computer where a diagnostic software program can be utilized for fault isolation.
A Duplexer is used to connect the separate receiver and transmitter outputs from the ARTU to the common antenna. This device is a signal filter and combiner, that is a switching unit and is designed for a minimum signal loss during both the receive and transmit operations.
By reducing antenna size and increasing affordability, this new system will make satellite-based voice and data connectivity practical for a whole new segment of the industry.
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