The inner workings of a Sprint 4G LTE cell site (pictures)

CNET goes behind the scenes at a Sprint cell site in San Francisco, as the carrier prepares to officially launch its 4G LTE network in the Bay Area.

Lynn La
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Sprint's LTE cell site

Although Sprint's 4G LTE network has already been available in some pockets of San Francisco for months, the carrier has yet to announce its official launching. Until then, CNET takes a look at one of the carrier's active cell sites in San Francisco, known as Site SF33XC664.

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Going down Van Ness

The site is located on the roof of the Medical Arts Building on Van Ness Avenue. When looking for an ideal location for a cell site, engineers involved in radio frequency design look at the surrounding typography, population, and traffic density of a given area.

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Signaler on the roof

Once a location is chosen, carriers must get clearance from municipality and zoning commissions. They then negotiate leasing terms with building landlords for every individual site. Currently, Sprint has 38,000 sites across the U.S.

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The subtle antenna

At this location, Sprint has installed three antennas on the roof. The range of each antenna depends on its location. For a site like this, this antenna is estimated to cover about a quarter square mile.

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One for 1,900MHz

Directly below the antenna are two radio heads (no, not that Radiohead). This unit is an RF amplifier that supports the 1,900MHz band frequency.

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The other for 800MHz

Below that is the RF amplifier for the 800MHz band. By installing the radio heads directly below the antenna (instead of nearby underground or at the cell site's base station, both of which are common methods), the carrier minimizes the amount of lost signal.

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Color-coded labeling

Cords that run throughout the antenna and the radio heads are wrapped in bright tape, with different colors representing different network speeds and bands. It helps engineers to quickly identify fiber optics for 4G LTE and 3G CDMA technology.

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Note from the FCC

Warning signs about radio frequency exposure are posted in various locations throughout the site.

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Joe Meyer, VP of network service

The vice president of Sprint's network service management, Joe Meyer, stands in front of the site's base station where signal traffic between phones and the network are regulated.

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Cut the blue wire!

Here, the top control panel handles LTE data, while the bottom two handles CDMA data and voice. The station does not support WiMAX technology.

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Room for expansion

The space below the panels are left intentionally empty to make room for more spectrum, if need be. Likely, the extra spectrum would be provided from Clearwire.

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Backup battery power

Next to the base station is a backup power unit made up of 12 deep-cycle batteries. If a site loses commercial power, the batteries are designed to provide between 4 and 8 hours of emergency power.

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Fiber back haul station

Data from the base station is fed through this fiber back haul station, which will then send signals through AT&T's (the incumbent cable company in the City) fiber cables. The signals travel about 10 miles out to Brisbane, Calif., where calls and Internet receptions are routed to the appropriate locations.

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The current time is...

At the very top of the base station is a white and red GPS antenna, which synchronizes information like the local time and location to your cell phone.

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Competitors staying close

Sprint isn't the only carrier to install a cell site here. Though you can see another one of its antennas on the left, one of AT&T's white antennas stands a few feet to the right of it.

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Engineers from Samsung

Two Samsung engineers (right) stand by at the cell site. A total of three OEMs -- Samsung, Ericsson, and Alcatel -- are providing the build-out for Sprint's expanding 4G LTE network.

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Aging technology

Next to Sprint's new base station is one of the carrier's own previous, 15-year-old base station (left), which is equipped with radio heads inside. To the right of it are two backup battery sources. The station only provides 1X, 3G, and voice technology, and will soon be decommissioned.

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MetroPCS is on the house

Behind Sprint's equipment is MetroPCS' own base station.

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In case there's confusion

A MetroPCS sticker labels the carrier's equipment.

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Once again, AT&T

Not far from both carriers' stations is AT&T's equipment as well.

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Consider us warned

The door leading to the cell site is riddled with more warning signs from different carriers cautioning against high amounts of radio frequency exposure.

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