Viscount724 From Switzerland, joined Oct 2006, 27192 posts, RR: 22 Posted (8 years 1 month 2 days 23 hours ago) and read 2210 times:
Most if not all early 747s (both -100s and -200s I believe) had some kind of housing a few feet long on the upper fuselage at the extreme rear of the upper deck (where the upper deck meets the rest of the fuselage). It's clearly visible in the first photo below. Some years later it was removed. The second photo is of the same aircraft many years later and it is gone.
N231YE From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 1 month 2 days 23 hours ago) and read 2203 times:
It was an antennae housing, but I forgot what antennae was inside of it. Someone asked this very question in an issue of Airliners Magazine, but that was long ago...and I don't know what happened to the issue.