Agency reduces power on 72-mile WLAN link

Computerworld - The High Performance Wireless Research and Education Network (HPWREN) has cut back the power it uses on a 72-mile WLAN link between San Diego and San Clemente Island.
Operating in the same 2.4-GHz frequency band used by wireless LANs, the agency reduced a power amplifier it uses from 1 watt to 250 milliwatts following complaints that the original configuration was illegal after a story about it appeared in Computerworld (see story).
Hans Werner-Braun, principal investigator for HPWREN, said the network, based at the San Diego Supercomputer Center on the campus of the University of California, San Diego, made the change last weekend on the long-shot connection to San Clemente Island in order to stay within Federal Communications Commission regulations for power levels on the 2.4-GHz band.
Computerworld received numerous e-mail complaints that HPWREN was in violation of FCC power limits following publication of its original story. Steve Bragg, a senior electronics engineer at Internet Telemetry Corp. in Tulsa, Okla., called the HPWREN San Clemente Island link illegal, saying, "If I was the FCC, I would bust these guys."
Werner-Braun said any violation of the power limits was unintentional and resulted from the fact that the personnel working on HPWREN primarily have expertise in computers and not radio technology. Based on research he has done in the past week, Werner-Braun said he could actually operate at "a much higher EIRP just by reducing the antenna input power and using huge high-gain antennas."
EIRP stands for effective isotropically radiated power, which is the power supplied to an antenna, plus its gain.
Instead, Werner-Braun said, HPWREN chose to reduce power to the 2-ft. parabolic antennas by 75%. Even at that lower power level, he said, HPWREN has managed to maintain the 72-mile link to San Clemente Island, although data throughput has now dropped to about 300K bit/sec.
The link is used to carry data from a seismograph, data logger and Global Positioning System receiver. It cost about $3,000 to build and install.
Computerworld has asked FCC officials for comments on the complaints about the San Clemente Island link, but the agency hasn't responded.
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