|  | H |
SECTION H — ELECTRICITY

|  | H04 |
ELECTRIC COMMUNICATION TECHNIQUE

|  | H04K |
SECRET COMMUNICATION; JAMMING OF COMMUNICATION

|  | H04K |
Note(s) The term "secret communication" includes secret line and radiation transmission systems, i.e. those in which apparatus at the transmitting station modifies the signal in such a way that the information cannot be intelligibly received without corresponding modifying apparatus at the receiving station.

|  | H04K 1/00 |
Secret communication (systems with reduced bandwidth or suppressed carrier Fulltext... Hierarchy... Expanded...H04B 1/66; by using a sub-carrier Fulltext... Hierarchy... Expanded...H04B 1/70; by multiplexing Fulltext... Hierarchy... Expanded...H04J; transmission systems for secret digital information Fulltext... Hierarchy... Expanded...H04L 9/00; secret or subscription television systems Fulltext... Hierarchy... Expanded...H04N 7/16)

|  | H04K 1/02 |
· | by adding a second signal to make the desired signal unintelligible

|  | H04K 1/04 |
· | by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band

|  | H04K 1/06 |
· | by transmitting the information or elements thereof at unnatural speeds or in jumbled order or backwards

|  | H04K 1/08 |
· | by varying the polarisation of transmitted waves

|  | H04K 1/10 |
· | by using two signals transmitted simultaneously or successively

|  | H04K 3/00 |
Jamming of communication; Counter-measures