Single-sideband modulation: Difference between revisions

Revision as of 21:21, 15 March 2003

Revision as of 17:36, 25 June 2003

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For this to work, the false carrier must be accurately adjusted to match the frequency of the original carrier. If the false carrier is mis-adjusted, the output signal will be frequency-shifted, making speech sound strange and '[[Donald Duck]]'-like.

If the wrong subcarrier is selected at [[intermediate frequency|IF]] conversion time, the audio signal will also be frequency inverted. This effect was used, in conjunction with other filtering techniques, during [[World War II]] as a method for speech [[encryption]]. Radio telephone conversations between the US and England were intercepted and 'decrypted' by the Germans; they included some early conversations between Roosevelt and Churchill.

Today (2001), such simple 'inverter'-based speech encryption techniques are easily decrypted using simple techniques and are no longer regarded as secure.