There is an interesting comparison between Arecibo and the Goldstone Solar System Radar (GSSR) here. Both have humongous EIRP but Arecibo just wins (or won) out. The GSSR has a 500 kW X-band (8.5 GHz) klystron into the DSS-14 70m dish which works out at around 130 dBW EIRP. Arecibo had 1MW at S-band (2.5 GHz) into a 305m dish so around 136 dBW. Any radio engineer will tell you a) that is a lot and b) don’t stand in front of it. Puerto-Rico has fewer aircraft passing over that might enter the beam so it was easier to schedule operations there but DSS-14 can point whereas Arecibo can’t (much). DSS-14 is still a critical element of the Deep Space Network so has a lot of money invested in it.
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