пятница, 4 сентября 2009 г.

The small series of the articles about Scramblers by MSM Group. Icom UT-110

Public conventional Scramblers. Part II.
Icom UT-110.
The dynamic analogue scrambler.

Author: SergUA6 6.0
Band Width ~ 3400 Hz
RX mode NFM


The example of UT-110 Scrambler's work is here.

Sonograms

pic.1 General view



Icom UT-110 - the dynamic analogue scrambler. The operation principle is well-visible from the sonogram.

The principle is not difficult. The speech is divided into fragments with duration approximately 4 seconds. These four seconds, are also divided into four fragments with duration about 1000 msec. The frequency, which divides the spectrum on two parts, is selected from each fragment (F1, F2, F3, F4), and then each of these parts is inverted.

The Four-seconds blocks are divided by sync pulses with duration about 200 msec. The sync pulse represents an audio-frequency(tonal) impulse. Generaly, that's all essential information.

Ofcourse, such scrambler cannot be considered as serious protection. It is weak by it's definition.

The main weakness is the very long durataion of fragments of scrambling about ~1000 msec and predictability. All 4-seconds blocks have identical frequencies F1, F2, F3, F4. All that allows to easily remove the main parameters of the scrambling and to restore speech.

On the other hand, all these minuses allow to provide protection against the simple listening by common, simple, relativaly cheap methods. The cost of the method is very importent, when it is used in mass productution. Such scrambling is much more relieble, and provides qualitative enough protection against simple listening, at least, it is much more reliable than the direct inversion, which is not cracked only the lazy people in our days.