The provisions of this paragraph do not apply to repeaters that transmit on the 1.2 cm or shorter wavelength bands. Before establishing a repeater within 16 km (10 miles) of the Arecibo Observatory or before changing the transmitting frequency, transmitter power, antenna height or directivity of an existing repeater, the station licensee must give written notification thereof to the Interference Office, Arecibo Observatory, HC3 Box 53995, Arecibo, Puerto Rico 00612, in writing or electronically, of the technical parameters of the proposal. Licensees who choose to transmit information electronically should e-mail to: email@example.com.
(1) The notification shall state the geographical coordinates of the antenna (NAD-83 datum), antenna height above mean sea level (AMSL), antenna center of radiation above ground level (AGL), antenna directivity and gain, proposed frequency and FCC Rule Part, type of emission, effective radiated power, and whether the proposed use is itinerant. Licensees may wish to consult interference guidelines provided by Cornell University.
(2) If an objection to the proposed operation is received by the FCC from the Arecibo Observatory, Arecibo, Puerto Rico, within 20 days from the date of notification, the FCC will consider all aspects of the problem and take whatever action is deemed appropriate. The licensee will be required to make reasonable efforts in order to resolve or mitigate any potential interference problem with the Arecibo Observatory.
The difference between 16 km and 10 miles is about 93 meters, the diameter of just the reflector itself is 305 meters, and the Arecibo grounds cover a somewhat larger area. So, if you add those factors up, I'd estimate you should figure on an easy +/- 500 meter ambiguity about where the 16 km boundary lies.
Taking that into account, the circle I've drawn around Arecibo Observatory on this map represents approximately 16.5 km from the center of the reflector.
The excerpts of US Title 47 CFR § 97 (Part 97) came from www.eCFR.gov and were current as of November 9, 2012.