Bandwidth Signal Mediums

The Radio Frequency Medium

The medium a frequency travels through effects bandwidth. Radio Frequency, or RF, travels through air much like sound. The higher the RF frequency, the less it will be affected by the environment and the more information it can carry. RF, however can be interfered by physical things such as walls, trees, clouds, buildings, etc. Non-physical things can also have an effect such as another RF being generated at a fairly identical frequency. This would cause a clash with the information carrying frequency. In either case, the signal could deteriorate.

Using Wire as a Medium

Different types of wires have an effect on bandwidth for cable and telephone. Coaxial cable used for television is designed for higher bandwidth because of transmitting both picture and sound, but still way too low to be used for anything large scale. Also, coaxial cable was originally designed for transmission of information in one direction only. New cables are being used to supply two directional communication, but it’s not currently available in all neighborhoods.

Phone lines are even worse yet. The wiring and service was originally only designed for voice communication. It’s designed to transmit around 14kHz, which is the average voice frequency. A 56kb dial modem tries to squeeze four bits on every wavelength. The resulting poor quality combined with the travel distance degrades the actual speed to much less. Trying to support a mass telecommunication environment with this wouldn’t be possible.

Photonics Air Medium

That’s where photonics comes in. With the frequency of a 1330nm wavelength laser being 225THz, an enormous bandwidth is available. Light can be sent through air, usually by infra-red, but the transmitter and receiver must be line of sight with no obstructions and distance is limited due to the openness and particles in the air. The laser doesn’t stay focused and spreads out the farther the distance, becoming less reliable. Also, dirt and water in the air can cloud the medium and weaken the laser signal. The result of these factors, keeps the bandwidth way below light’s true potential.

Photonics Fiber Medium

The best medium is for the laser to be transmitted through thin glass fibers from destination to destination. This keeps the light focused within the fiber providing very little loss. Present day optical fibers are manufactured with glass so free of impurities that it’s clearer than air itself and the core carrying portion is thinner than a human hair. “A single optical fibre is able to carry the equivalent of 300,000,000 simultaneous telephone calls” states Technical Insights analyst Michael Valenti (NewsRx 5-1).

Brandon Yautz
April 2006