Washington county resolves radio interference involving Nextel
The Clark Regional Emergency Services Agency, Vancouver, WA, has resolved interference to the agency’s radio communications system that was associated with a Nextel Communications cell site in the sheriff’s precinct in the western part of Clark County. Clark County, WA, borders Multnomah County, OR, and the city of Vancouver lies across the Columbia River from Portland.
“We made some measurements and found that we were getting intermodulation interference in our radios. Our consultant, who helped with the measurements, gave Nextel a frequency set to use on its site that probably would work. Nextel retuned the site several months ago, and it has been working fine since,” said Rick Lazo, CRESA’s senior communications system technician.”
Lazo said that, prior to the retune, police officers were “pretty upset” with gaps in the radio system’s coverage.
“The West Sheriff’s Precinct practically didn’t have any communications. Voice and data were wiped out in their parking lot and around the one tower that Nextel had on that side,” he said.
Lazo said that he hired Adcomm Engineering, Woodinville, WA, to consult his agency about the problem, both for Adcomm’s expertise and its test equipment.
“We don’t have a good spectrum analyzer, just service monitors,” Lazo explained.
Lazo said that he spent about a week’s time and $700 for consulting services to resolve the interference. He said that since the retuning, he hasn’t received any more complaints about system performance than normal.
Nearby Portland, OR, has documented a lot of interference problems connected with cellular-type wireless telephone systems, including Nextel’s, that affect its public safety radio communications. Lazo said that he believes his agency has had less of an interference problem because Portland’s Nextel sites are loaded with more channels, which increases the potential for intermodulation interference. He said that Nextel has fewer sites using fewer channels in his area.
Tom Griffin, CRESA’s director, said that the agency’s regional radio system serves every public safety agency in Clark County. Most agencies use the regional 800MHz infrastructure that provides multiple channels of voice and data communication and interoperability between agencies, a vital feature during emergencies. All law enforcement agencies and some fire departments receive data over the system to on-board computers in their vehicles. Agencies served by CRESA that use VHF frequencies are “patched” to the 800MHz system to enable them to communicate with agencies on that system.
In addition to its 9-1-1 and radio dispatching responsibility, the agency provides emergency management coordination and oversees a contract for ambulance service to a part of the county.
