The circuit uses a fast Norton amplifier in a configuration that excites a 75 ohms line. The circuit is suggested by National's 1994 Linear Applications Handbook.
This shield, found in old English documentation, appears with variations elsewhere in this section...
This complementary or bilateral emitter follower was found in American documentation from the 90s....
This configuration that functions as a zener diode was found in an English publication from 1976....