Figure 3.5-1. Assembly of a 9-meter dish near Gainesville, Florida, to pick up Apollo 17 radio communications, November 1972. Credit: Sven Grahn.
The Italian radio telescope at Arcetri, near Florence, picked up the voice communications of the Apollo 11 astronauts as they descended to the Moon. Professor Guglielmo Righini, director of the observatory, and chemistry-physics professor Salvatore Califano of the University of Florence, vividly describe their scientific eavesropping on the conversations of the Apollo astronauts:
Professor Righini explained that at Arcetri, the physicists from Florence followed the American space endeavor from its beginning, staying permanently in indirect contact with the spacecraft and listening to the conversations of the astronauts when they occurred on a particular wavelength to which the Arcetri instrument was tuned and when, before the Moon landing, the American spacecraft orbited around the near side of the Moon.
-- Attraverso i sassi lunari studieremo il sistema solare, by Carlo Degl’Innocenti, on L’Unità, 22 July 1969, page 5.
These signals are very strong evidence that the Apollo spacecraft actually did go all the way to the Moon for several reasons. First of all, the very large antennas used by these non-NASA receivers are highly directional: in other words, they only hear signals that come from the very small spot in the sky towards which they are pointed. If the Apollo signals were picked up by the antennas while they were pointed at the Moon, the signals had to come from the Moon. These signals could not arrive from, say, an Earth-orbiting artificial satellite, because such a satellite would have move in the sky much faster than the Moon in order to stay in orbit.
Secondly, the Apollo signals exhibited Doppler shift: their frequency shifted when they moved periodically towards and away from the receivers as the spacecraft orbited around the Moon. The values of this shift allowed to determine the speed of the vehicles and confirm that they were orbiting around the Moon at the speed and distance stated by NASA.
In other words, voices from lunar orbit were received independently on Earth by researchers. Anyone claiming a conspiracy would therefore have to explain, in technical detail, how these signals could be faked so well as to fool scientists or would have to accuse Sven Grahn and professors Righini and Califano of being liars.