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 H04B 1/66; by using a sub-carrier H04B 1/70; by multiplexing H04J; secret telegraph or data transmission systems H04L 9/00; secret or subscription television systems 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