Assuming he is watching U.S. TV shows provided by AFN, he will need an NTSC tuner like this one.
If you decide to go with this particular tuner, he will also likely need an audio adapter.
More than likely this will work, but you may want to verify that he is trying to watch NTSC service (U.S. analog programming) and not ATSC (digital) or PAL service.
my son-in-law is deployed in Afganistan. He has a TV coax input, but his TV only has RCA A/V input jacks. He has asked me to send him an adapter / converter so that he can watch TV.. Radio Shack and Best Buy have converters that will go from RCA to coax, but they say they don't have a way to convert coax to RCA A/V.
Any help will be greatly appreciated! Thanks!