NH prepares for a radio-occultation of Pluto and Charon just after the physical pass through the orbital plane of the Pluto system. The earth broadcasts a signal and NH picks it up. Not sure where that is listed in the timeline video.
[EDIT]
The Pluto - Earth occ occurs at 12:42:55 UTC, with the REX instrument active (high-gain antenna + signal processing module).
The Charon - Earth occ occurs at 14:30:44 UTC, again with REX active.
REX has to listen to the transmitters from earth, and as can be seen in the video, it's not far from the Sun. The REX paper (address below) advises that the separation is 0.23 degrees. The Deep Space Network has been assigned to pump out a minimum of 10kW at a baseband frequency of 7.1GHz (preferably 20kW) to provide the occultation "artificial radio star light", which has to be picked out from the broadband signal from the sun. A pretty decent task for the REX module.
http://pluto.jhuapl.edu/Mission/Spacecraft/Payload.php
http://www.boulder.swri.edu/pkb/ssr/ssr-rex.pdf
Regards,
Tony Barry
WSAAG