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Fiber Opti Am

Is fiber-optic technology in our future?

by Roald Steen AJ0N/LA6US

Photo A. Fiber optics is a rapidly evolving communications technology which is of interest to the amateur radio community.

Fiber optics is a segment of the communications industry which is evolving rapidly. While fiber optics is used chiefly for land and undersea communications cables, there are also uses lor this technology in amateur radio.

One of the most interesting applications of fiber optics in amateur radio may be as a substitute for coaxial cables. As you know, coaxial cables are lossy. The longer the coaxial cable and the higher the operating frequency, the more the signal will be attenuated in a coaxial cable. The falling cost of fiber-optic receivers and transmitters makes fiber optics an attractive substitute for coaxial cables.

We are used 10 having the receiver and the transmitter in the shack, but the correct location for these dcviccs is really right next to the antenna. Through fiber optics, it is possible to select these favorable locations for the transmitter and the receiver.

The equipment in your shack could produce both the frequency and the modulation of the signal which you arc transmitting, Once these two components of your signal are generated in Lhe shackt they can be fed from a fiber-optic transmitter through a fiber-optic cable to Lhe antenna, where an RF amplifier could be mounted in a weatherproof enclosure.

Both the fiber and the electric power to the transmitter must run up to the antenna. This can be achieved, in the case of a solid-stale transmitter, simply by supplying the 12 volts DC, needed to operate the transmitter, through low voltage wiring.

Also, for the receiver from end, the best location is as close to the antenna as possible in order to avoid attenuation of the received signal and pickup of noise. Coaxial cables pick up some electronic noise. By running fiber-optic cable from the receiver front end to the receiver in your shack you eliminate all pickup of electromagnetic

Photo A. Fiber optics is a rapidly evolving communications technology which is of interest to the amateur radio community.

been adopted by some mobile amateur radio manufacturers. Aviation and marine radio manufacturers are also adopting the fiberoptic cable as a link between the control head and the transceiver

Fiber-optic cables can be used for a number of other control and communications purposes. For example, fiberoptic cables may be used to connect one or several remote receivers to a repeater.

A significant advantage of fiber optics over other communications cables is its enormous bandwidth. A bandwidth of gigacycïes is possible. This bandwidth limitation is not a limitation inherent in the fiber itself, but rather in the input and output devices, i.e. the optic receivers and transmitters.

The technology of fiberoptic receivers and transmitters is steadily improving. Scientists working for a Japanese company recently fed information at a rate of 20 gigacycles through a fiber-optic cable exceeding 600 miles. This equals a capacity of around 3,000 television channels. Commercial devices are lacking such laboratory records, yet the capabilities of modern commercial fiber-optic systems can be impressive.

noise in the feedline. Fiber-optic cables are completely immune to electromagnetic noise. You can run a fiber-optic cable right next to the mosi powerful RF devices without any RF getting into the signal propagating through the cable.

Mobile Radios

Manufacturers of mobile radios have started to embrace fiber optics. Some mobile radios now come wilh a small but advanced control head which communicates with the transceiver in the trunk through a fiber-optic cable. This technology has also

Optie Fiber Types

There are three main types of optic fibers. Plastic fibers have high attenuation ratings which limit this fiber type to cables that cover up to a few hundred feet. But plastic fibers are cheap and easy to install, and are therefore an attractive material for short cable runs.

Regular glass fibers have some spreading of the signal, since internal reflections from the edges of the fiber ensure that a signal which is sent from one end is received somewhat smeared out in the other end. This smearing limits the amount of infor-

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