|  | H |
SECTION H — ELECTRICITY

|  | H04 |
ELECTRIC COMMUNICATION TECHNIQUE

|  | H04L |
TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (typewriters Fulltext... Hierarchy... Expanded...B41J; order telegraphs, fire or police telegraphs Fulltext... Hierarchy... Expanded...G08B; visual telegraphy Fulltext... Hierarchy... Expanded...G08B, Fulltext... Hierarchy... Expanded...G08C; teleautographic systems Fulltext... Hierarchy... Expanded...G08C; arrangements common to telegraphic and telephonic communication Fulltext... Hierarchy... Expanded...H04M; selecting Fulltext... Hierarchy... Expanded...H04Q)

|  | H04L |
Note(s) This sub-class deals with transmission of signals having been supplied in digital form and includes data transmission, telegraphic communication, and methods or arrangements for monitoring.

|  | H04L 1/00 |
Arrangements for detecting or preventing errors in the information received (correcting synchronisation Fulltext... Hierarchy... Expanded...H04L 7/00; arrangements in the transmission path Fulltext... Hierarchy... Expanded...H04B)

|  | H04L 1/02 |
· | by diversity reception (in general Fulltext... Hierarchy... Expanded...H04B 7/02)

|  | H04L 1/04 |
· · | using frequency diversity

|  | H04L 1/06 |
· · | using space diversity

|  | H04L 1/08 |
· | by repeating transmission, e.g. Verdan system

|  | H04L 1/10 |
· | by using codes designed for error detection with or without automatic error correction, e.g. using Hamming code, using parity-checking

|  | H04L 1/12 |
· | by using return channel

|  | H04L 1/14 |
· · | in which the signals are sent back to the transmitter to be checked

|  | H04L 1/16 |
· · | in which the return channel carries supervisory signals, e.g. repetition request signals

|  | H04L 1/18 |
· · · | Automatic repetition systems, e.g. van Duuren system

|  | H04L 1/20 |
· | using signal-quality detector [3]

|  | H04L 1/22 |
· | using redundant apparatus to increase reliability [3]

|  | H04L 1/24 |
· | Testing correct operation [3]

|  | H04L 3/00 |
Arrangements for converting one code into another code (Fulltext... Hierarchy... Expanded...H04L 25/49 takes precedence; code conversion in general Fulltext... Hierarchy... Expanded...H03K 13/24)

|  | H04L 3/02 |
· | Arrangements for converting codes in which each character is represented by the same number of equal-length code elements into error-detecting or error-correcting codes, or vice versa, e.g. five-unit code into seven-unit code with three marking and four spacing elements

|  | H04L 3/04 |
· | Arrangements for converting codes in which each character is represented by the same number of equal-length code elements into dot-and-dash codes or vice versa

|  | H04L 5/00 |
Arrangements affording multiple use of the transmission path (multiplex communication in general Fulltext... Hierarchy... Expanded...H04J)

|  | H04L 5/02 |
· | Channels characterised by the type of signal

|  | H04L 5/04 |
· · | the signals being represented by different amplitudes or polarities, e.g. quadriplex

|  | H04L 5/06 |
· · | the signals being represented by different frequencies (combined with time-division multiplexing Fulltext... Hierarchy... Expanded...H04L 5/26)

|  | H04L 5/08 |
· · · | each combination of signals in different channels being represented by a fixed frequency

|  | H04L 5/10 |
· · · | with dynamo-electric generation of carriers; with mechanical filters or demodulators

|  | H04L 5/12 |
· · | the signals being represented by different phase modulations of a single carrier

|  | H04L 5/14 |
· | Two-way operation using the same type of signal, i.e. duplex (conditioning for two-way transmission in general Fulltext... Hierarchy... Expanded...H04B 3/20)

|  | H04L 5/16 |
· · | Half-duplex systems; Simplex/duplex switching; Transmission of break signals

|  | H04L 5/18 |
· · | Automatic changing of the traffic direction

|  | H04L 5/20 |
· | using different combinations of lines, e.g. phantom working

|  | H04L 5/22 |
· | using time-division multiplexing

|  | H04L 5/24 |
· · | with start-stop synchronous converters

|  | H04L 5/26 |
· · | combined with the use of different frequencies

|  | H04L 7/00 |
Arrangements for synchronising receiver with transmitter

|  | H04L 7/02 |
· | Speed or phase control by the received code signals, the signals containing no special synchronisation information

|  | H04L 7/04 |
· | Speed or phase control by synchronisation signals

|  | H04L 7/06 |
· · | the synchronisation signals differing from the information signals in amplitude, polarity, or frequency

|  | H04L 7/08 |
· · | the synchronisation signals recurring cyclically

|  | H04L 7/10 |
· · | Arrangements for initial synchronisation

|  | H04L 9/00 |
Arrangements for secret communication (in general Fulltext... Hierarchy... Expanded...H04K)

|  | H04L 9/02 |
· | by adding a key-signal to make the desired signal unintelligible

|  | H04L 9/04 |
· · | Arrangements for generating key-code characters

|  | H04L 11/00 |
Exchanges; Connections between exchanges; Connections between exchanges and substations

|  | H04L 11/02 |
· | Details

|  | H04L 11/04 |
· · | Switch-boards

|  | H04L 11/06 |
· · | Answer-back mechanisms or circuits

|  | H04L 11/08 |
· · | Monitoring arrangements

|  | H04L 11/10 |
· · | Allotting numbers to messages; Counting characters, words, or messages (counting in general Fulltext... Hierarchy... Expanded...G06M)

|  | H04L 11/12 |
· · | Testing equipment; Routine testing

|  | H04L 11/14 |
· · | Current supply arrangements

|  | H04L 11/15 |
· · | Arrangements for remote connection or disconnection of substations or of equipment thereat

|  | H04L 11/16 |
· | Party-line systems

|  | H04L 11/18 |
· | Systems affording broadcast facilities; Systems affording conference facilities

|  | H04L 11/20 |
· | Message switching systems (permutation-code selecting Fulltext... Hierarchy... Expanded...H04Q 3/02)

|  | H04L 11/22 |
· · | Manual relay systems, e.g. push-button switching

|  | H04L 11/24 |
· · · | with perforated tape storage

|  | H04L 11/26 |
· | Arrangements for preventing the taking of data from a data transmission channel without authorisation [2]

|  | H04L 13/00 |
Details of the apparatus or circuits covered by groups Fulltext... Hierarchy... Expanded...H04L 15/00 and Fulltext... Hierarchy... Expanded...H04L 17/00

|  | H04L 13/02 |
· | Details not particular to receiver or transmitter

|  | H04L 13/04 |
· · | Driving mechanisms; Clutches (in general Fulltext... Hierarchy... Expanded...F16)

|  | H04L 13/06 |
· · | Tape or page guiding or feeding devices

|  | H04L 13/08 |
· · | Intermediate storage means

|  | H04L 13/10 |
· · | Distributors

|  | H04L 13/12 |
· · · | Non-mechanical distributors, e.g. relay distributors

|  | H04L 13/14 |
· · · · | Electronic distributors (in general Fulltext... Hierarchy... Expanded...H03K 17/00)

|  | H04L 13/16 |
· | of transmitters, e.g. code-bars, code-discs

|  | H04L 13/18 |
· | of receivers

|  | H04L 15/00 |
Apparatus or local circuits for transmitting or receiving dot-and-dash codes, e.g. Morse code (teaching apparatus therefor Fulltext... Hierarchy... Expanded...G09B; telegraph tapping keys Fulltext... Hierarchy... Expanded...H01H 21/86)

|  | H04L 15/03 |
· | Keys structurally combined with sound generators [2]

|  | H04L 15/04 |
· | Apparatus or circuits at the transmitting end

|  | H04L 15/06 |
· · | with a restricted number of keys, e.g. separate key for each type of code element

|  | H04L 15/08 |
· · · | with a single key which transmits dots in one position and dashes in a second position

|  | H04L 15/10 |
· · · | combined with perforating apparatus

|  | H04L 15/12 |
· · | with keyboard co-operating with code-bars

|  | H04L 15/14 |
· · · | combined with perforating apparatus

|  | H04L 15/16 |
· · | with keyboard co-operating with code discs

|  | H04L 15/18 |
· · | Automatic transmitters, e.g. controlled by perforated tape

|  | H04L 15/20 |
· · · | with optical sensing means

|  | H04L 15/22 |
· · | Apparatus or circuits for sending one or a restricted number of signals, e.g. distress signals

|  | H04L 15/24 |
· | Apparatus or circuits at the receiving end

|  | H04L 15/26 |
· · | Operating only on reception of predetermined code signals, e.g. distress signals, party-line call signals

|  | H04L 15/28 |
· · | Code reproducing apparatus

|  | H04L 15/30 |
· · · | Writing recorders

|  | H04L 15/32 |
· · · | Perforating recorders

|  | H04L 15/34 |
· · | Apparatus for recording received coded signals after translation, e.g. as type-characters

|  | H04L 17/00 |
Apparatus or local circuits for transmitting or receiving codes wherein each character is represented by the same number of equal-length code elements, e.g. Baudot code

|  | H04L 17/02 |
· | Apparatus or circuits at the transmitting end

|  | H04L 17/04 |
· · | with keyboard co-operating with code-bars

|  | H04L 17/06 |
· · · | Contact operating means

|  | H04L 17/08 |
· · · | combined with perforating apparatus

|  | H04L 17/10 |
· · | with keyboard co-operating with code-discs

|  | H04L 17/12 |
· · | Automatic transmitters, e.g. controlled by perforated tape

|  | H04L 17/14 |
· · · | with optical sensing means

|  | H04L 17/16 |
· | Apparatus or circuits at the receiving end

|  | H04L 17/18 |
· · | Code selection mechanisms

|  | H04L 17/20 |
· · | using perforating recorders

|  | H04L 17/22 |
· · | using mechanical translation and type-bar printing

|  | H04L 17/24 |
· · | using mechanical translation and type-head printing, e.g. type-wheel, type-cylinder

|  | H04L 17/26 |
· · | using aggregate motion translation

|  | H04L 17/28 |
· · | using pneumatic or hydraulic translation

|  | H04L 17/30 |
· · | using electric or electronic translation

|  | H04L 19/00 |
Apparatus or local circuits for step-by-step systems

|  | H04L 21/00 |
Apparatus or local circuits for mosaic printer telegraph systems

|  | H04L 21/02 |
· | at the transmitting end

|  | H04L 21/04 |
· | at the receiving end

|  | H04L 23/00 |
Apparatus or local circuits for systems other than those covered by groups Fulltext... Hierarchy... Expanded...Fulltext... Hierarchy... Expanded...H04L 15/00-H04L 21/00

|  | H04L 23/02 |
· | adapted for orthogonal signalling [2]

|  | H04L 25/00 |
Dc systems

|  | H04L 25/02 |
· | Details (circuits in general for handling pulses Fulltext... Hierarchy... Expanded...H03K; in line transmission systems in general Fulltext... Hierarchy... Expanded...H04B 3/02)

|  | H04L 25/03 |
· · | Shaping networks in transmitter or receiver, e.g. adaptive shaping networks (impedance networks per se Fulltext... Hierarchy... Expanded...H03H) [2]

|  | H04L 25/04 |
· · · | Passive shaping networks [2]

|  | H04L 25/06 |
· · | Dc level restoring means; Bias distortion correction

|  | H04L 25/08 |
· · | Modifications for reducing interference; Modifications for reducing effects due to line faults

|  | H04L 25/10 |
· · | Compensating for variations in line balance

|  | H04L 25/12 |
· · | Compensating for variations in line impedance

|  | H04L 25/14 |
· · | Channel dividing arrangements

|  | H04L 25/16 |
· · | Interpolating arrangements; Removal of redundancy; Predictive arrangements [2]

|  | H04L 25/18 |
· · | Arrangements for inductively generating telegraphic signals (induction coil interrupters Fulltext... Hierarchy... Expanded...H01H 51/34; dynamo-electric generators Fulltext... Hierarchy... Expanded...H02K)

|  | H04L 25/20 |
· · | Repeater circuits; Relay circuits

|  | H04L 25/22 |
· · · | Repeaters for converting two wires to four wires (in general Fulltext... Hierarchy... Expanded...H04B); Repeaters for converting single current to double current

|  | H04L 25/24 |
· · · | Relay circuits using discharge tubes or semiconductor devices

|  | H04L 25/26 |
· · · | Circuits with optical sensing means

|  | H04L 25/28 |
· · · | Repeaters using modulation and subsequent demodulation

|  | H04L 25/30 |
· | Non-synchronous systems

|  | H04L 25/32 |
· · | characterised by the code employed

|  | H04L 25/34 |
· · · | using three or more different amplitudes, e.g. cable code

|  | H04L 25/36 |
· · | with electric or magnetic storage of the signals before transmitting or receiving to increase transmission speed

|  | H04L 25/38 |
· | Synchronous or start-stop systems, e.g. for Baudot code

|  | H04L 25/40 |
· · | Transmitting circuits; Receiving circuits (repeater circuits, relay circuits Fulltext... Hierarchy... Expanded...H04L 25/52)

|  | H04L 25/42 |
· · · | using mechanical distributors

|  | H04L 25/44 |
· · · | using relay distributors

|  | H04L 25/45 |
· · · | using electronic distributors (electronic distributors in general Fulltext... Hierarchy... Expanded...H03K 17/00) [2]

|  | H04L 25/46 |
· · · | using tuning forks or vibrating reeds

|  | H04L 25/48 |
· · · | characterised by the code employed (Fulltext... Hierarchy... Expanded...H04L 25/49 takes precedence) [2]

|  | H04L 25/49 |
· · · | using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels [2]

|  | H04L 25/493 |
· · · · | by transition coding, i.e. the time-position or direction of a transition being encoded before transmission [3]

|  | H04L 25/497 |
· · · · | by correlative coding, e.g. partial response coding or echo modulation coding [3]

|  | H04L 25/50 |
· · · | with electric or magnetic storage of the signals before transmitting or receiving to increase transmission speed

|  | H04L 25/52 |
· · | Repeater circuits; Relay circuits

|  | H04L 25/54 |
· · · | using mechanical distributors

|  | H04L 25/56 |
· · · | Non-electrical regenerative repeaters

|  | H04L 25/58 |
· · · | using relay distributors

|  | H04L 25/60 |
· · · | Regenerative repeaters with electromagnetic switches

|  | H04L 25/62 |
· · · | using tuning forks or vibrating reeds

|  | H04L 25/64 |
· · · | Start-stop regenerative repeaters using discharge tubes or semiconductor devices

|  | H04L 25/66 |
· · · | Synchronous repeaters using discharge tubes or semiconductor devices

|  | H04L 27/00 |
Ac systems

|  | H04L 27/02 |
· | Amplitude-modulated carrier systems, e.g. using on/off keying; Single sideband or vestigial sideband modulation [2]

|  | H04L 27/04 |
· · | Modulator circuits (in general Fulltext... Hierarchy... Expanded...H03C); Transmitter circuits

|  | H04L 27/06 |
· · | Demodulator circuits (in general Fulltext... Hierarchy... Expanded...H03D); Receiver circuits

|  | H04L 27/08 |
· · | Amplitude regulation arrangements

|  | H04L 27/10 |
· | Frequency-modulated carrier systems, i.e. using frequency-shift keying

|  | H04L 27/12 |
· · | Modulator circuits (in general Fulltext... Hierarchy... Expanded...H03C); Transmitter circuits

|  | H04L 27/14 |
· · | Demodulator circuits (in general Fulltext... Hierarchy... Expanded...H03D); Receiver circuits

|  | H04L 27/16 |
· · | Frequency regulation arrangements

|  | H04L 27/18 |
· | Phase-modulated carrier systems, i.e. using phase-shift keying

|  | H04L 27/20 |
· · | Modulator circuits (in general Fulltext... Hierarchy... Expanded...H03C); Transmitter circuits

|  | H04L 27/22 |
· · | Demodulator circuits (in general Fulltext... Hierarchy... Expanded...H03D); Receiver circuits

|  | H04L 27/24 |
· · | Half-wave signalling systems

|  | H04L 27/26 |
· | Systems using multi-frequency codes

|  | H04L 27/28 |
· · | with simultaneous transmission of different frequencies each representing one code element

|  | H04L 27/30 |
· · | wherein each code element is represented by a combination of frequencies