Wireless Link


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In April, 2007, the CSU-CHILL site Internet connectivity was upgraded using a wireless modem link to the nearby University of Northern Colorado. UNC provided high speed 25 Mbps bandwidth to the CSU campus.


Link Hardware

The modem used is an Exalt EX-5r-c IP, along with an Andrew C-band antenna. The EX-5r-c IP provides 55 Mbps data rates, at distances up to 30 miles, depending on the antenna used. The link reliability is greater than 99.999% (five nines). The link operates at one of three frequency bands:

  • 5.25 - 5.35 GHz
  • 5.47 - 5.725 GHz
  • 5.725 - 5.85 GHz

The operating frequencies are set sufficiently away from the second harmonic of the CSU-CHILL radar (5.45 GHz). Additional capacity, up to 200 Mbps, may be added by upgrading the modem firmware.

The modem is fully self-contained, and rated for outdoor use. It is designed to be mounted on the antenna mast, and receives power through a Power-over-Ethernet scheme.

Site preparation

The first steps in setting up the wireless link was to identify the type of antenna needed and the sites where they would be mounted. An engineer from the modem company visited the CSU-CHILL site, after setting up a test antenna on a rooftop at UNC.

After making measurements at CHILL, the company decided on the Andrew C-band external antenna. This antenna also provides some isolation from the CHILL radar's high-power microwave signal due to its directivity.

Installation of the Wireless Link

Engineers from the modem company visited CHILL site again, after setting up the wireless dish and modem at the UNC site. They then mounted the C-band antenna, with weather-proof radome, on the side of the CSU-CHILL office building. The link was aligned optically, as well as using a spectrum analyzer.

Next, the modem was mounted to the antenna mast. The N-type connectors with low-loss cables were attached to the antenna. The Ethernet data and power cable was run into the CHILL office building, to the network wiring closet. Here, a Power-over-Ethernet injector and power supply was installed, since the existing CHILL network infrastructure does not support PoE.

The link was then tested using the netperf network performance monitoring tool. Netperf was allowed to run overnight between the CHILL site and a computer at UNC. After establishing a satisfactory link, more performance testing was done with a computer located at CSU Engineering. Once reliable communications was established, the existing T1 link between CSU-CHILL and CSU Engineering was disconnected and replaced with the wireless link.

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