Chris Fallen on Twitter @ctfallen
Are you in the SE USA or Caribbean? Consider tuning your radios to approximately 5.125 or 8.175 MHz starting Saturday 11/3 for the possibility tuning in the Arecibo HF campaign. Bonus for tuning ~50 microsec (?) ISR pulses (0.6% duty cyc) at 430 MHz, perhaps offset by the HF freq— Chris Fallen (@ctfallen) November 3, 2018
Arecibo HF campaign pretty much all day and night through 11/9, mostly at ~5.1 MHz. When their local foF2 is up, try ~8.2 MHz?— Chris Fallen (@ctfallen) November 4, 2018
I'm a frozen-in @uafhaarp guy but also must admit I'm just a little bit jelly @NAICobservatory can run high-power HF nearly 24/7 during their campaigns!
Past, Present and Future of Active Radio Frequency Experiments in Spacehttps://t.co/HfpKiqPrPp— Chris Fallen (@ctfallen) November 5, 2018
Arecibo Observatory on Twitter @NAICobservatory
HAM Radio and WebSDR’s listening to Arecibo
Signal in SC pic.twitter.com/yjDuJCxjOU— Paul Jones (@NN4F_Radio) November 3, 2018
Additional reports that #arecibo observatory HF campaign is transmitting pulsing signals on 5100 khz. I see those on/off carriers but unsure if it actually is Arecibo. #hamradio #radio #swl #haarp .@ctfallen pic.twitter.com/e3LIKyC2T6— www.SpaceWatch.US (KM0MMM) (@KM0MMM) November 3, 2018
And now, off again - now on 😎— 🇮🇹 Marco (@BlackApple62) November 3, 2018
Merkours, if you have time, have a look at my video of a 31 july 2017 experiment with nice fireworks on the waterfall:https://t.co/fwGed0ShJV
Something I also have in JN53: just off now pic.twitter.com/85SdokI6Ue— 🇮🇹 Marco (@BlackApple62) November 3, 2018
Arecibo Observatory Enhanced HF Ionospheric Heating Instrument
Arecibo Observatory, PR-625, Arecibo, Puerto Rico
- Antennas: 6 crossed dipoles, 5.1 MHz (3 x 25.5 meters) 8.175 MHz (3 x 14.5 meters), 98 meter Cassegrain screen hexagonal sub-reflector, 305 meter dish primary reflector. 
- Frequency: 5.1 - 8.175 MHz
- Power: 600,000 Watts (600 kW, 100 kW x 6)
- ERP: 200,000,000 Watts (200 MW)
The investigators will use the enhanced instrument cluster at Arecibo Observatory (AO) to gain new insight into the complex nature of the space-atmosphere interaction region (SAIR). The new High Frequency (HF) heating facility with the ISR (Incoherent Scatter Radar) and other instruments provides a unique opportunity to study heating-related aeronomic and plasma physics problems. This includes the rapidly-imaged observation of airglow at 557.7 nm, 630.0 nm and 427.8 nm during ionospheric “heating” campaigns to understand the role of HF-heating in generating plasma bubbles, or modulating them if already present, and to understand the role of secondary suprathermal electrons in producing airglow at different wavelengths. This research will also yield insight to the heating process, including locating ionospheric “hot-spots”, yielding details of the electron collision process, elucidating the role of Langmuir and ion-acoustic waves in the strongly heated regions, and study of heating effects in Sporadic E. The latter study will include Ca+ metal-lidar observations as further defined by 555.7 nm imaging as well as ISR and HF radar results. HF heating of the ionosphere offers a unique opportunity to investigate the plasma heating process and its effects on the neutrals in a controlled (experimental) fashion. Outside of the heating campaigns, a database of 630 nm all-sky camera images from other locations will be assembled collaboratively to investigate the global context of the omnipresent ~1 hr period ionospheric waves, and associated dynamics, first identified with the AO ISR. This work will utilize other AO instruments, including the resonance and Rayleigh lidars, to investigate the role of wave coupling from lower atmospheric regions. Also, a proposed new CCD camera will allow high speed imaging to better understand HF heating effects and linking optical and radar meteors to study meteoroid aeronomy. The response of the SAIR to sudden changes in the environment caused by heating will be explored with the collaborative use of multiple instruments, thus informing numerous geophysical research areas. The multidisciplinary nature of this work will help to establish collaborations with plasma physicists, modelers, and space weather scientists. It will also advance the AO cluster capabilities with the addition of a User-Owned, Public Access (UOPA) high frame rate CCD to the current imager and help in establishing international collaborations. Students representing minorities from local universities in Puerto Rico will be encouraged to participate in observations and data analysis. They will be involved in the improvements of the optical systems including training on AO instrumentation and the application of these instruments to study aeronomy of the SAIR.
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 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. 
HAARP and the Sky Heaters (FAQ)
Ionospheric Heaters: How HAARP really works
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