Cell towers and distributed antenna systems (DAS) are pillars of our digital society. Smartphones and the calls, YouTube videos and business deals we harness them for are dependent on the quality of the cellular connections in our homes and places of work. Cell towers empower us to do all of these things, and when connections break down due to massive crowds like those at a sports game, DAS boost our signals. What happens, then, when cell towers and DAS experience faults and drop signals? To test a cellular data network, towers and DAS require specific testing methods such as PIM testing, cable & antenna analysis and carrier-approved cell fiber tests. Towers will also require antenna alignment to direct signals to other towers.
How Do Cell Towers Work?
We rely on cell towers for almost every type of communication in our society. But how exactly do they transfer our data? Cell towers transfer information through cables, specifically fiber optic cables in most cases, which lead to the antenna at the tower’s apex. From there, we can divide towers into two distinct breeds with differing ranges of bandwidths.
- RF Cell Towers
- An RF cell tower is mounted with three antennae, each covering a 120° angle to maximize both signal coverage and communication with other towers. These are the standard cell sites.
- Microwave Cell Towers
- A microwave cell tower concentrates its signal into a single beam and locks on to a very distant tower, which simultaneously is locking on to the first tower, until their signals are synchronized. Data is then shared back and forth. The powerful bandwidth a microwave antenna generates allows for the transfer of data over long distances.
What is a DAS?
A Distributed Antenna System, or DAS, is an array of antenna nodes spread over a defined area to both amplify and aggregate cellular signals. Facility owners choose to replace a single high power antenna with a grouping of low power antennas in order to compensate for blind spots in coverage, distant cell towers or signal-blocking materials. A DAS will also lead to a wider signal bandwidth, which means faster data speeds. To test the connection speed of a DAS, technicians analyze the fiber optic cables that connect each antenna node with the instruments discussed below.
Cell Tower Test Equipment
The following test instruments are designed for testing an array of different cell tower performance characteristics from troubleshooting fiber cable faults to locating passive intermodulation.
PIM Testing
PIM, or passive intermodulation, is a byproduct of loose contact between inconsistent metal surfaces channeling a current, especially cell tower or DAS fiber cables as they transmit data. This conductive contact generates meddlesome PIM signals, which interfere with intentional RF transmissions. PIM analyzers, then, test for PIM by performing distance-to-PIM tests and discovering the source of the network performance failure while verifying the quality copper or fiber cables.
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Cable & Antenna Analysis
Cable and Antenna Analyzers, or Sweepers, measure VSWR / return loss, cable loss, insertion loss and distance-to-fault for copper cables. Commonly, a technician may choose to run a sweeper over the copper cable section of a tower above the long lines of fiber and simply replace the copper section, which can save costs in comparison to renting a PIM analyzer.
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Cell Fiber Testing
Cell fiber test kits are wireless carrier-approved bundles of fiber testing equipment which include OTDRs and other testing devices like visual fault locators, optical power meters and fiber inspection scopes. These all-in-one kits allow technicians to verify fiber cables with instruments approved by carriers like Verizon.
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Antenna Alignment
Intended for use with cell towers, not DAS, antenna alignment tools ensure a tower’s antenna are directed towards the next tower and connected with the network. Carriers like Verizon, AT&T and Sprint require antenna alignment tools to optimize the link reliability of their towers, especially for long-range microwave towers.
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Other Test Equipment
ATEC carries an extensive inventory of cellular network equipment which consists of other equipment used at cell site and for other types of cellular network testing like:
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