SA Update: version 6.0.6.4.

SA Update: Version 6.0.6.4
Reverse synthesis of FSK/MFSK signals.

New in version 6.0.6.4:

• the minor problems are solved
• some algorithms are optimised
• ability of reverse synthesis FSK/MFSK of signals is added

What is the reverse synthesis for? There is the certain problem with the signals, which have poor enought quality. If, in SA, it is possible to define parametres, and there is the possibility to save the signal in the better quality compare to initial one, then it is desirable to do it. We will consider a standard example.

The record Piccolo-12 from the site http://www.signals.taunus.de/FFT/PICC-MK12-TFC.jpg, by the way, is the only one record, which is managed to be found in Internet by me. It is well-visible, that the level of interferences is very high. Standardly used, in such cases, amplitude limiters do not make the situation better.

Nevertheless, SA allows to define paremeters of this signal reliebly enough, and moreover, SA allows to save the resulting signal in the much better quality.

Reverse synthesis removes both out-of-band noises and interferenсes and in-band ones, which are hardly can be removed by other tools. The difference is perceptible both by ear and by sonograms:

• initial signal
• restored signal

Reverse synthesis in SA, restores the signal in the same frequency positions, and with the same frequency spacing and speed of manipulation, as an initial signal.

There are more examples:

BulDiplo - is the high-speed enough signal.

On the record of Chinese modem MFSK-64 - almost complete suppression of noise is well visible.

Ofcourse, reverse Synthesis, as any other tool, has it's own field of application.

No need to use it too much and all the time, no need to expect that this tool will solve all the problems with the noisy records.

The positive accuracy and thoughtfulness is needed, some experience and skills are also required.

Attention please: Never represent similarly edited records for analysis.

Everywhere and always I insist that the analyst should have for the analysis completely initial, not touched (and not edited) material. Only the analysit solves what to do with this material and how to do
it.

Reverse synthesis is the tool of analysis, but not the tool of decoration of the records for the further analysis.

Good Luck!

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.

Analysis of QAM-16.

The example of analysis of the real signal.
Analysis of the record of QAM-16 signal.

The example of analysis of the real signal 2008_21_12_fm.wav

The video clip to this article is attached!

The first mandatory step is the testing of the record on suitability for analysis. This step does not guarantee exact diagnostics, and the main objective of the test is the tentative estimation of chances of success. If will be found out, that the record is made with rough disturbances, has strong distortions or was exposed to a compression, then the chances of carrying out of the qualitative analysis are extremely small.

In generall, the there are no big problems, and it is possible to hope that the efforts spent for the analysis will be not vain. The record seems to has a notable blockage/obstruction of level on the low frequencies, but it is not the reason for refusal of the analysis.

We get, where possible, the preliminary "measures" from the signal, at the same time we are marking that the blockage/obstruction is really present. When we say "Measures" here, we mean:

• preliminary, and rough enough estimates, of the spectrum's centre of the signal
• presence and direction of distortion/defect of the spectrum, of spectrum's width and etc

All that can be useful further for specification conclusions and summarys.

We receive clock frequency of manipulation, through two methods, both methods give identical results. The line of the clock frequency is clear and bright enough, that gives grounds to consider the received value relieble.

We check the version that it is FSK, MFSK or something like that. The version does not prove to be true, the histogram does not show any obvious allocation of frequencies.

There are two not so clear lines, with frequencies of ~1667 and ~1336 Hz, In the module of obtaining of harmonics, in the fourth degree. The standard error in this case, that, usually, an analyst does not check the following higher harmonics, in this case there is a risk to skip brighter and correct/clear enough picture. However on this signal, the higher harmonics do not give any lines at all.

Usually, the purpose in the exponentation module in a degree of harmonic's getting, the is to get any possible lines, in case when lines are gotten, the chances to open the signal are very great. Not always quality of the signal or modulation allows to make it, but in our case there are hooks. It is necessary, starting with Suppositions that it is a PSK-like signal to prove a choice of one of frequencies as carrier frequency. Of course, in hard cases, it is necessary to sort out simply all variants, but that does not forbid to prove the first variant somehow. On preliminary "measures" taking, Fc - is defined at level of 1320-1350 Hz, it is logical to make the first, and probably not correct supposition that carrier will be will be somewhere in this area and the choice falls on frequency ~1336.

Lanuch Phase Plane module and specify the fourth degree, that degree, in which the lines were detected. Please Pay attention that the preliminary "not proved" carrier, has much bigger amplitude, and looks as real carrier much more convincingly. But it is also necessary to pay attention that the common tendency of the non-uniform spectrum is saved and approximately conform to initial non-uniformity. It means that ,easily, at the expense of the distorted frequency characteristic such non-uniformity in levels of the lines can be objective, and is not mandatory that the strongest line is really carrier, that is is possible that a preliminary choice and was not wrong, but correct.

We start the process of constellation's mapping, after some time of capturing and synchronisation of the internal generators, the picture is more or less stabilised, and it will be possible to take advantage of the corrector for attempts to restore the signal.

The corrector successfully copes with the task, and it becomes absolutely clear that the researched signal is QAM-16, but it has some features. On the lines of the external big square, the positions, which do not coincide with positions of standard constellation QAM-16 are used. It is desirable to understand somehow what these positions are andd how they are related with the signal.

By having included mapping of transitions in the constellation, It is possible to notice that constellation's points produce the square in the main constellation QAM-16. If to look on the mapping transitions more attentive, then it is possible to notice that this additional square, is not linked by transitions to the main constellation. It is typical sort of constellation for QAM modulation, with so-called re-trainings. Re-trainings are injected into the signal specially, with the purpose to provide qualitative work of the adaptive corrector in the demodulator. It solves tasks of the qualitative demodulation of a signal in very hard and difficult conditions of reception, since re-trainings are known in advance to the receiving side, and the very effective tuning by time and setup of the adaptive corrector of the receiver are realized by re-trainings.

Having played with the semiautomatic corrector, and having selected more correct degree (12th) it is possible to receive the final signal with high quality enough. For the control this signal can be saved and cheked up for how should look the record with the absence of distortions or at their minimum value.

Much more regular allocation of the spectrum is visible, and besides, the signals of such quality, as a rule, do not call difficulties at the analysis, because practically at once in 12th degree, it is possible to recive value of the carrier, and the ideal constellation on phase plane. But in practice such signals are rare exception, than a rule.

The small video clip is attached to the article. The video clip, where the main course of process of getting of parametres of the signal and its correction is showed.

Good Luck!

An example of the signal from UDXF forum's discussion

Unfortunately, the record is not qualitative: or the receiver is RX, or the recording devices are distorting the signal.

But nevertheless.

8 frequency channels with space between frequencies 300 Hz and speed of manipulation (Baud rate) in the channel 100 Hz.

Ofcourse, it is possible to spend deeper analysis, but we already have enough data(including width of the spectrum), what is enough for a reliable identification of the signal.

It is classed as Japanese Military 8 freq. The description of this signal is in our signal's base http://signals.radioscanner.ru/base/signal159/ .

The small example: the signal from discussion in UDFX Group.

The marker of free channel of the sea coastal station SITOR from Turkey.