Actually, I never thought of it before your last post, but why didn't anyone use a hand communicator to call Lexington?
(we really don't have a facepalm smiley?)
It's disheartening to like and defend something and then really see a huge plot hole big enough to drive the Fesarius through. In over 30 years I never noticed they didn't use a hand communicator.
I always assumed that the M-5 had a damping field around the ship blocking communications. Similar to what they did in "Journey to Babel" when they limited the transmission to the alien ship from that fake Andorian guy.