Tuesday, November 13, 2007


Mobile phones and the network they operate under vary significantly from provider to provider, and nation to nation. However, all of them communicate through electromagnetic microwaves with a cell site base station, the antennas of which are usually mounted on a tower, pole, or building.

The phones have a low-power transceiver that transmits voice and data to the nearest cell sites, usually 5 to 8 miles away. When the cellular phone or data device is turned on, it registers with the mobile telephone exchange, or switch, with its unique identifiers, and will then be alerted by the mobile switch when there is an incoming telephone call. The handset constantly listens for the strongest signal being received from the surrounding base stations. As the user moves around the network, the mobile device will "handoff" to various cell sites during calls, or while waiting between calls it will reselect cell sites.

Cell sites have relatively low-power radio transmitters which broadcast their presence and relay communications between the mobile handsets and the switch. The switch in turn connects the call to another subscriber of the same wireless service provider or to the public telephone network, which includes the networks of other wireless carriers.

Monday, November 05, 2007

Aerial tramway

An aerial tramway is one or two set cables (called track cables), one endless loop of cable (called a haulage rope), and two passenger cabins. The fixed cables give support for the cabins. The haulage rope, by means of a grip, is solidly linked to the truck (the wheel set that rolls on the cables). The haulage rope is frequently driven by an electric motor and being connected to the cabins, moves them up or down the mountain.
Two-car tramways use a jig-back system: A large electric motor is situated at the bottom of the tramway so that it successfully pulls one cabin down, using that cabin's weight to help pull the extra cabin up. A similar system of cables is use in a funicular railway. The two passenger cabins, which carry from 4 to over 100 people, are positioned at opposite ends of the loops of cable. Thus, as one is coming up, the other is going down the mountain, and they pass each other midway on the cable span.
Some aerial trams have only one cabin, which lends itself better for systems with small altitude changes along the cable run.