|The Arecibo SETI observatory|
"It is basically the same as HAARP for the science, except that HAARP was in the Auroral Region, where the physics of the ionosphere is quite different with all the energetic particles and magnetic fields," Penn State Electrical Engineering Professor Jim Breakall, WA3FET, told ARRL. "HAARP also had 3 gigawatts of effective radiated power, where Arecibo will only be about 200 megawatts." The Arecibo Observatory Amateur Radio Club, KP4AO, is headquartered at the research facility, which celebrated its 50th anniversary last fall.
The National Science Foundation and Cornell University, which previously operated Arecibo Observatory, contracted with Penn State's Electrical Engineering Department to construct the "new and enhanced" HF ionospheric instrument. It will be used to study the interaction between HF radio energy and ionospheric plasma.
The new facility will replace an earlier ionospheric heater in Islote, Puerto Rico, that was destroyed by Hurricane Georges in 1998. Rather than rebuild that installation, the new instrument will use the observatory's 1000 foot dish for its antenna. This will keep all research activities involving ionospheric modification at the observatory proper. Plans call for a design based on a Cassegrain-screen concept of phased array at the bottom of the dish feeding a sub-reflector mesh that hangs above the dish from three support towers. Breakall and his team of graduate students at Penn State have done all of the electrical design and modeling of this new antenna system.
"There are three crossed-dipoles for 5.1 MHz and another three for 8.175 MHz, forming an array that will beam energy up to a net mesh reflector that will hang from the three big towers," Breakall explained. "This Cassegrain screen will then reflect energy back down to the 1000 foot dish and beam an effective radiated power of hundreds of megawatts up to the ionosphere to modify it." Each dipole is fed from a 100 kW transmitter, yielding a total transmitted power of 600 kW.
An even earlier HF ionosphere-heating antenna system also was suspended from the platform above the dish and driven by a single 100 kW transmitter over a frequency range of 3 to 10 MHz. That design suffered from arcing problems and was taken out of service in the 1970s.
Scale aside, Breakall said, while HAARP also tried to modulate the ionosphere's naturally flowing currents to create VLF and ELF for submarine communication, Arecibo "has much weaker currents, and that probably will not work," he said. On the other hand, he said, "Arecibo has a big advantage over HAARP in that the same 1000 foot dish can be used for diagnostics with the 430 MHz incoherent scatter radar that can measure things such as temperature, density, winds, etc, as they are modified. HAARP has nothing like this."
Breakall said he does not anticipate that the new Arecibo ionospheric research facility will attract the same degree of controversy that HAARP has over its history, but he conceded that it's possi