If you're ever in DC and want to see more of this kind of stuff, definitely check out the Spy Museum. It's unbelievable the lengths both countries went to for even the most basic of intelligence!
Coincidentally I happen to be reading a book on the same subject. From memory, how the commies picked up the signal was even more interesting. In a false chimney attached to the Embassy they installed a remotely controlled Yagi antenna, that could be pointed at a particular target. At the top of the 'chimney' was a copper v-shaped dome serving to gather and focus the weak signal from the typewriters. The signal from the antenna was then sent through an amplifier and cable down a tunnel into the Soviet sector. The transmission from the typewriter consisted of a compressed burst-mode signal hidden in the side-bands of near-by television transmissions, making it virtually impossible to detect using normal bug detecting equipment. When the existence of such was reported to the ambassador, he said: can you bring us 100% proof the commies are bugging us.
