I recall a book I read back in middle school (ca. 1981), where humanity had sent an astronaut to check out signs of an intelligent race or something like that, but he disappeared. Earth then sends his younger brother to see what happened, but using an older spacecraft because the first mission used the only up-to-date one Earth had. Also they refuse to let him take any weapons, to avoid any possible provocation.
On the way something impacts his windshield, punching a hole through it. He thinks either it was a meteoroid, or a laser beam--but no Earth laser beam could punch a hole that small from more than 1000 miles away.
He later finds the aliens, who are blobs with tentacles or something like that (my memory's hazy), and he's out in his space suit. He doesn't have a laser to defend himself with, so he uses his communicator (or something like that), setting it to CODE, its most intense setting. That seems somehow to disable the alien, and soon it's in trouble. He comes out to it and tries to pull it away from danger, but of course with nothing to push/pull against, his efforts are in vain--but it turns out that convinces the aliens that humanity really means them no harm, so he returns to Earth a hero.
That's as best I can remember the story. Does it ring any bells for anyone?