| H | SK | SECTION H — ELECTRICITY |
| H04 | KL | ELECTRIC COMMUNICATION TECHNIQUE |
| H04K | UKL | SECRET COMMUNICATION; JAMMING OF COMMUNICATION |
| H04K 1/00 | HGR | Secret communication (ciphering or deciphering apparatus per seG09C; systems with reduced bandwidth or suppressed carrier H04B 1/66; spread spectrum techniques in general H04B 1/69; by using a sub-carrier H04B 14/08; by multiplexing H04J; transmission systems for secret digital information H04L 9/00; secret or subscription television systems H04N 7/16) |
| H04K 1/02 | UGR1 | | . | by adding a second signal to make the desired signal unintelligible |
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| H04K 1/04 | UGR1 | | . | by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band |
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| H04K 1/06 | UGR1 | | . | by transmitting the information or elements thereof at unnatural speeds or in jumbled order or backwards |
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| H04K 1/08 | UGR1 | | . | by varying the polarisation of transmitted waves |
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| H04K 1/10 | UGR1 | | . | by using two signals transmitted simultaneously or successively |
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| H04K 3/00 | HGR | Jamming of communication; Counter-measures (counter-measures used in radar or analogous systems G01S 7/00) |