Scramblers: Harris AVS, Analog Voice Security

Harris AVS

Analog Voice Security

The record of Harris AVS

Author: SergUA6

Band Width ~2700 Hz

Low Range 300 Hz, in this example ~240-260, shift is possible

Count of Carriers 24 subchannels 112-113 Hz

Step between carriers ~112-113 Hz between centres of subchanneles

RX mode SSB

Sonograms:

pic.1 Generall view

The analogue not synchronizable scrambler, speech spectrum with band in 2700 Hz. It is broken into 24 subchannels in width approximately 112-113 Hz, these subchannels are replaced and partially inverted, time shifts are not used in this scrambler. The subchannels ocated densely without protective intervals as for example at 04XK100. Probably time shifts aren't used because of use on SW, though Codan them uses. This isn't direct inversion.

The small series of the articles about Scramblers by MSM Group. Direct Inversion.

Direct inversion.
Final Part III.
Direct inversion of speech spectrum.

Author: SergUA6 6.0
Band Width 2700 - 3400 Hz, it can vary, depends of tasks.
Low Range 100 - 300 Hz, it also can vary.
RX mode All types of modulation.

Sonograms

pic.1 Spectrum of inverted speech

pic.2 Spectrum of normal speech

1. The example of inverted speech, point(frequency) of inversion is 3600 Hz.

2. Exactly restored inverted speech.

Direct (simple) inversion - is the direct(simple) inversion of spectrum. It is one of the most widespread sorts of speech's masking. It is easily recognised by ear (in the case of absence of the strong interferences) and by the form the spectrum: it is well-visible on the spectrum, that the main energy is concentrated in the upper band of the frequencys, what is unusual for speech. Those who saw a normal spectrum of speech and inverted atleast once , will unmistakably define inversion further, even if it is got mixed up with other features. For today this sort of masking Makes impression unless on absolutely trustful people. Direct inversion is easily defined, easily removed, and in general it is more suitable for creation of insignificant minor problems , than for masking.

Nevertheless, the direct inversion is still widely spread today, by virtue:

• of it's simplicity
• of the absense of synchronization (the weak place of all synchronized scramblers)
• of the posibility to work in conditions of the strong interferrences

And anyway the function of the fast hiding of information is realized, althought the direct inversion isn't a barrier even in real-time.

The inverted spectrum is very easily formed by following steps:

• the frequency of inversion usually around 3000-4000 is selected
• after multiplication of an initial signal (speech) with this frequency is occuring
• then the lower lateral is selected from resulted DSB signal. This lateral is the inverted spectrum of the initial signal

The modern tools allows to do it very qualitatively. The same manipulations with the signal are used for restoring.

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.

The small series of the articles about Scramblers by MSM Group.

Public conventional Scramblers. Part I.
Icom UT-109.
The static double-band analogue scrambler.

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

The Scrambler is here

Icom UT-109 - the static double-band analogue scrambler. An operation principle of it is easily defined on the sonogram. The initial spectrum of speech is divided/separated on two parts, by the
conditional/relative line (frequency),and each part is inverted. The breaking line of the spectrum is an original key.

Listening Resistance is much more lower than for scrambler Icom UT-110, and generally comes nearer to direct inversion, and do not exceeding direct inversion so much.

The ear is extremely powerful analyzer oriented on speech, and loss even half of spectrum on the good signals does not lead to disastrous loss of articulation, especially if the language is native and the subject of the speech is not strongly specific.

The widespread enough error is that scrambler UT-109 represents itself the direct inversion.

In reality, in very many cases, it is really possible rather successfully to de-scramble this masking/mask as direct inversion, especially if the second half of spectrum is rather narrow. For example as on the first, second or fourth fragment in the record, but for the qualitative and a complete recovery the special approach with taking into account features of the scrambling is necessary.