What a shame if they have to tear it down, they just finished the build out to the full array a couple of years ago!

I was fortunate to get a tour of the site about 10 years ago as my friend Steve W4YHD was the Chief Engineer, quite impressive! I have some photos (35mm film, not digital) which I need to scan.  The HAARP transmitters were true AM transmitters as they were used to heat the ionosphere and generate e.l.f. waves by modulating the carrier with low frequency audio tones, very inefficient (but all elf transmission schemes suffer from lack of efficiency), ,many megawatts of HF energy used to excite milliwatts (or perhaps microwatts?) of elf radiation from the ionosphere.

See:
http://vlf.stanford.edu/research/experiments-haarp-ionospheric-heater

    I recall that they had a Radar on site and were supposed to shut down in case an aircraft flew through the beam. They also had an ICOM R72 receiver so they could listen before transmitting so as not to cause QRM !  The whole lashup was powered by a series of 5 generators driven by diesel locomotive engines.   The transmitter was actually a bunch of final amplifiers, solid state driver and a 3cx5000 PA tube, housed in trailers below the antenna array, each trailer housed a number of 3cx5000 PA's - the PA's were fed by an HP synthesizer (don't recall the model #, might be in one of my photos) and fed with equal lengths of coax so all PA's would be in phase. There was a method to shift the phase across the array so as to change the shape and direction of the beam. The antennas were bow-tie dipoles broadband from 3-10MHz.  The whole thing was controlled by Sun Sparc workstations from a master control room.  Just for fun I tuned up one of the transmitters on 7.290 MHz AM to see if I could strap Ashtabula Bill W8VYZ, of course it was daytime and I don't think anybody was affected!

   Was hoping to make a return trip to see the fully built out site but its looking very questionable at the moment.

73 Warren K2ORS