Diagnosing the Ionosphere
Read about research using HAARP
An interest in amateur radio and a passion for public broadcasting eventually led Steve Floyd (BSEET, ’80) to serve as chief RF engineer and designer for the highest-power, short-wave transmitting station in the world. This station, called the High Frequency Active Auroral Research Program (HAARP), can transmit up to 3,600 kilowatts via an array of 180 crossed dipole antennas on towers covering 42 acres in Alaska’s bush country.
HAARP is a research facility for studying plasma physics and radio science involving the Earth’s Ionosphere. Changes in the Ionosphere’s plasma in this near-space region are related to space weather, which generate the beautiful auroras. Space weather can also interfere with all forms of radio communications and navigation systems, or generate electromagnetic impulses that disrupt the power grid.
While passive radar stations around the world can measure the effects of space weather, HAARP and similar facilities — including ones in Peru, Puerto Rico, Russia, and Norway — can transmit a focused high-frequency (HF) electromagnetic radio beam into the ionosphere to study different effects (See page 20). The HAARP website describes the intensity of the HF signal in the ionosphere as less than 3 microwatts per cm2 — tens of thousands of times less than the Sun’s natural electromagnetic radiation that reaches the earth. However, this is enough power to do ground breaking Ionospheric physics research.
It wasn’t a love of space science, however, that drove Floyd to his role with HAARP, but a passion for amateur radio and public broadcasting. Floyd had earned his ham radio license when he was 13 and spent the next few years building radio equipment and experimenting with wire antennas in his back yard. During that time, he also started listening to public radio. “One of my goals was not just to study EE,” he recalls, “but to find a way to get involved in the high power transmitter engineering side of radio broadcasting.”
Floyd’s experience at WUVT sparked an interest for high power RF technology, eventually putting him in charge of the most powerful RF antenna in the world
When he visited Virginia Tech as a high school student and discovered the student-run WUVT radio station, he knew he had found a good fit. He returned home and promptly earned his FCC commercial broadcast licenses. “Back then, you had to have an FCC commercial radiotelephone license to be a radio station disc jockey.” Floyd earned his FCC First Class radiotelephone license, enabling him to serve officially as a radio station chief engineer. When he enrolled at Virginia Tech as a student, one of the first things he did was join WUVT. “Within a week of joining, I was on the air doing a radio show,” he says. Although he continued with ham radio, most of his extracurricular time was spent with the campus radio station, working as a disc jockey and station engineer.
During his senior year at Tech, the WUVT engineering team upgraded from a 770 W transmitter to a much larger and complex 3,000 W transmitter. “We received an old transmitter and lovingly rebuilt it, and redesigned the entire WUVT transmitter system including the installation of a new high power broadcast antenna on Lee Hall,” he says. “We did all the work ourselves, and we prided ourselves on being as professional as we possibly could.”
The new WUVT transmitter system was based on ceramic-metal tube RF amplifier technology for the power amplifier. “I really fell in love with that higher-powered RF technology,” he says.
After graduating in 1980, Floyd worked in the defense industry in the Washington, D.C. area, designing radio transmitters, receivers, and radar systems. While working for E-Systems (acquired by Raytheon), he earned his MSEE degree from The Johns Hopkins University in 1991. In 1995, he joined the HAARP team. “My past experience with the new transmitter for WUVT lit a fire of interest in me for that high power RF technology. I’d always been looking for an opportunity like HAARP,” he says. HAARP employs 180 20 kW each custom designed transmitters using ceramic-metal tube RF amplifiers. “It’s essentially a larger version of the WUVT system!” he says.
When Floyd joined HAARP, the initial 18-transmitter build-out was experiencing problems. “We were able to completely redesign the existing system, plus build 30 more modified transmitters and antennas. By 1998 we had 48 transmitters operating in a 60 MW phased-array system. “Everything was working well and we had some great science results from researchers using the facility.” In 2004, the final build-out began and by 2007, HAARP was up and operating at the planned 180 transmitter/antenna system.
HAARP can transmit up to 3,600 kilowatts via an array of 180 crossed dipole antennas on towers covering 42 acres in Alaska’s bush country.
Designing and building a research facility of that size and complexity is not without problems. One of the early issues was defining the very technology required and creating it. “We had many debates as to whether to use the new solid-state or ceramic-metal tube transmitter technology,” Floyd recalls. “I had experience with both and preferred to use tubes, due to the inherent ruggedness and simplicity of construction.” HAARP is a planar phased antenna array of 12 columns by 15 rows, creating a highly interactive environment. “The transmitter interactions, or “mutual coupling,” between the closely spaced antennas would generate widely varying load impedances across the array. A tube amplifier is by far the most rugged amplifier type that can withstand this harsh environment. It is also more sound architecturally and less costly to build.”
Tubes are so rugged, that when operating under extreme conditions, all they do is get hot, he says. “We have lots of cooling air in Alaska.”
The required operating mode flexibility of the HAARP system and a desire to minimize any possible interference to other radio users was also a challenge. Most high-power broadcast transmitters are designed for one modulation type or service, such as FM or AM. HAARP needed the flexibility of operating in AM, FM, CW, or pulsing with user defined shaped rise and fall times. “We needed to limit the transmitted signal occupied bandwidth on the dial,” he says.
The team designed for a very pure output signal. “When other users of the radio spectrum saw the planned extreme high radiated power, they were concerned that our unintended radio harmonics and spurious emissions would be correspondingly large — that we’d interfere with them.” So, one of the specifications was for the transmitters to be 100 times, or 20 dB, better in harmonic and spurious emissions than any other transmitters ever built. The tuned plate tank output circuit used in tube amplifiers inherently provides a low harmonic output in addition to rugged durability, according to Floyd. “The required signal purity output was a huge challenge and we met it.”
In spite of its name, HAARP is not supposed to be musical. However, in 1998 when the facility first started at 48 transmitters, the maintenance staff would ask Floyd why they were hearing tones when we were transmitting. “They should not have been hearing anything. That meant there was arcing going on in the antenna system. We found there were missing wire connection welds from an antenna contractor.” The team waited until the dark of night, then transmitted a 1,000 Hz amplitude modulated tone. Listeners would indicate where the tone was loudest in the antenna wiring. They would spot a blue flame and then repair each defective connection.
His experience at Virginia Tech gave him an uncommon background, Floyd says. “I developed a love of high-power transmitter design and RF engineering from the wonderful teaching of my EE professors at Tech. The enthusiasm in the EE department and at WUVT was infectious. Not only did I succeed well in defense electronics, but then I found HAARP.”
It’s rare these days to find an EE comfortable with designing and building high-power transmitters. “I was tailor-made for this job,” Floyd says.