How Does Encryption Work on a Two Way Radio?

Encryption modifies a voice signal using a coding algorithm. An encryption key controls this algorithm. The encryption key is used by the transmit and receive radios to enable the voice signal to be coded and decoded for both radios. Therefore, all radios communicating must have matching encryption keys, or encryption won't work. There are several different methods for encrypting voice signals:

Simple Inversion:
Inversion scrambling inverts the frequencies and volume of the voice signal. The Icom UT-109 Scrambler Unit uses the simple inversion technique.

Hopping Inversion:
This method adds a greater degree of security than simple inversion. Using this method, the frequencies and frequency rates change irregularly. This causes a voice signal that that appears to "hop" all over a number of different frequencies and frequency rates.

Rolling Code Inversion:
Rolling code inversion uses a method where the voice signal is inverted at a constantly changing rate. It starts at an upward inversion frequency direction and climbs to the upper limit. Then, it reverses direction and inverts at lower frequencies until it reaches the lower limit. The Icom UT-110 Scrambler Unit uses this inversion technique.

20/03/2006