| H | SK | ELECTRICITY |
| H04 | KL | ELECTRIC COMMUNICATION TECHNIQUE |
| H04B | UKL | TRANSMISSION [4] |
| H04H | UKL | BROADCAST COMMUNICATION (multiplex communication H04J; pictorial communication aspects of broadcast systems H04N) |
| H04J | UKL | MULTIPLEX COMMUNICATION (peculiar to transmission of digital information H04L 5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N 7/08; in exchanges H04Q 11/00) |
| H04K | UKL | SECRET COMMUNICATION; JAMMING OF COMMUNICATION |
| H04L | UKL | TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) [4] |
| H04M | UKL | TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08) |
| H04N | UKL | PICTORIAL COMMUNICATION, e.g. TELEVISION [4] |
| H04Q | UKL | SELECTING (switches, relays, selectors H01H; wireless communication networks H04W) [1, 2009.01] |
| H04R | UKL | LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) [6] |
| H04S | UKL | STEREOPHONIC SYSTEMS [3] |
| H04W | UKL | WIRELESS COMMUNICATION NETWORKS [2009.01] |