SA update to version 6.2.2.8

SA update to version v 6.2.2.8

This is planned updating.

The new element in the general options is added.


Internal management of markers is reconsidered. Appearance and the size of the markers has been changed.

It is problematic enough to surely catch the markers by mouse with the thickness in 3 pixels, on the big monitors. Although it is required not so often, it may cause some inconveniences.

Correct independent work of two and more Phase Plane modules is realized. Some users actively use this possibility, and in old versions it worked not correctly.

We also prepeared the demo clip, which shows how to work with the bottom panel of tools. In this clip, we finish the review of the basic SA working window, and in The further we will countine to make demo clips about work with concrete modules.

All demo clips are recommended to be started on monitors with the permission not less then 1024х768 in mode Normal size 96 DPI.

The list of demo files of own SA format are located in special section of the site => Video examples on use SA.

Good Luck.

SA: How to work with OFDM module. How to apply new features of OFDM module on practice. Practical examples on real signals from the air.

SA - how to work with OFDM module.

Several practical examples on the real signals.

Full version of this really interesting tutorial is here.

After version 6.1.0.5 and article SA OFDM module, constellations in channels has appeared, we received several letters with questions about how to use OFDM module and what are practical possibilities of constellations in the channels.

Even taking into account those difficulties, which have been described in previous article, SA OFDM module represents powerful tool. Operation with this tool we will be considered more detailed in this article.

In this small tutorial we took 4 real signals from the air to work with in SA OFDM Module.

Here is the signals from the air, which are used for analysis in this tutorial:

1) DAB

2) OFDM-59

3) WinDRM

4) Q15X25

I do not post the whole artilce in the blog, because it will take too much space, not because of text, but because of pictures.

Please, follow the link to see whole article with all pictures, and interesting features inside.

My personal opinion: It will be very interesting to read for everyone.

SA OFDM module improvement: constellations in channels.

Phase constellations in the channels of OFDM signals.

As usually, we will try to apply new options on the qualitative signal, with well-known parameters. In the first, it will allow us to estimate possibilities of the new method basically, and in the second, will give accurate enough representation of how to apply this method on real signals. For this purpose we have synthesized signal OFDM test2.wav.

Parameters of the test2.wav signal:

Number of channels - 30

Manipulation in the channels - pi/4 DQPSK

Step between channels (frequency net/grid)- 80 Hz

Manipulation speed - 66.6(6) Hz

Sampling rate of signals formation - 6400 Hz

Symbols length (LS) with CP, in samplings - 96

Length of defensive interval (LG), in samplings- 16

Symbols length (LU), block size IFFT/FFT, in samplings - 80

Preliminary, I wish to pay attention to one widespread enough mistake at the work with OFDM module. Very often in records of OFDM signals, there is a pause at the beginning. This pause it is not visible on a spectrum, because it is short enough and simply masks. Selecting a fragment of a signal for the analysis in OFDM module and capturing this pause, will strongly reduce efficiency of calculations, if the fragment is short enough. For example: we have 40 symbols for calculation of correlation triangle, while in reality we can have only 10 or less symbols, because the main body will get on absolutely not informative pause fragment. We do not speak about zero level, it can be pause in signal transmission, which somehow has gotten into record.

Example:

Such situations should be considered, it Is necessary be simply attentive. Especially it concerns to short signals. SA Free inserts a zero fragment into beginning of signals always, while SA Full in this respect, works more correctly.

Let's open in SA the test signal and select a fragment, please pay attention, we select the fragment from the beginning of the file, because we know that the signal is synthesized, and absolutely precisely does not contain any pauses. Now, let’s call OFDM module with default settings on, and start search for correlative triangle. There is no necessity to wait for the end of calculations, very often the triangle, which is not calling doubts, can be formed very fast, the program can be stopped at any moment. Although, in doubtful cases, it is better wait until the end of procedure.

If everything has been done correctly, the triangle will be positioned with it's top precisely on the yellow marker automatically, because we are working right now with the ideal synthesized signal.

Let's select the first channel (the lower channel) by double click on the graphic. Now let's include constellation mapping also by double click on the necessary record in the list. Actions order does not play a special role. Further, it is possible to observe constellation in the lower channel moving on the signal symbol-by-symbol. Now it is visible, that in absolute corners it is PSK-8, in relative PSK-4, all is correct, it is classical pi/4 DQPSK.

Selecting other channels on the graphic's spectrum by single click, and moving on the signal symbol-by-symbol, it is possible to receive constellation of any channel.

In the video clip - this procedure is shown visually. Sometimes it is much better to see something once, for better understanding.

While we were making this video clip there was small problem: As far as constellation's points, on an ideal signal are the real points in one pixel, they weren't visible in the video clip. Thus, it was necessary to change mapping algorithm. Thereupon, for everyone who has version 6.1.0.5, it is necessary to update it to version 6.1.0.5a.

There is some thin moment, both absolute, and the relative constellations will be always precisely oriented on axes on any channel. Stable orientation of constellations, is a result of ideality of conditions of analyzed signal. These conditions are unstable, it is enough to shift the marker from triangle's top on the left slope, and from exact orientation on axes for absolute angles remains nothing. While for relative constellation everything stays former.

Why it occurs? Shift on the good side of triangle, as you should remember from the previous articles, guarantees a choice of one of correct LU. The quantity of LU in OFDM signal with CP is equal to LG+1. Remember the picture:

All LU differ from each other by phase shifts. Initially, while the marker was precisely at top of triangle, the latest LU was processed, and as this LU is "parent" of all other LU on it, at observance of all conditions, it is possible to demodulate the symbol and the whole signal. Actually this LU is the purpose of demodulator, because other LU mostly are spent on distortions in the signal.

That is why, as soon as we go away from the "true LU", we receive casual phase shift in absolute angles, while it is not reflected anyhow on relative angles.

To complete the picture, it is necessary to consider one more moment. We loaded the signal's fragment precisely from the first symbol, from beginning of the file. What if we will load file from random fragment? In this case, everything remains same: absolute angles will be randomly shifted, even if the yellow marker will stand precisely at triangle top. Relative remain stable.

What has happened? Isn't LU now "not native", after all, it is last LU in the complete symbol? LU is still "native", but if to speak more correctly, LU is the most authentic from all others, because distortions will reach it in the last moment. But now we got "not native" symbol!:) The program considers it as first symbol, while in practice we do not really know it. Yes, yes, in OFDM everything is so coordinated: symbol number, and number of LU, both sampling rate, and shift on frequency all that is coordinated. If one of these parameters is not that one, which should be, then chaos begins in absolute angles:)

Fortunately we have strong enough order in relative angles. Although, it is also not very stable.

For this reason, relative sorts of manipulations are so widespread in OFDM.

In reality, all is not so terrible as it is represented, the matter is that even not native symbol, and not native LU, at exact observance of all other parameters(such as the sampling rate and shift on frequency) do not threaten with anything deadly, except, a turn of absolute constellation relatively axes, of what we were convinced just now. The constellation is drawn correctly, and to calculate the angle of an error and to compensate it for each channel is possible. It is not an easy task, but this task has decisions.

In practice, any not distorted LU suits for the analysis, basically it is not important which number has the symbol. The maximum that it is possible to lose, in this case, is the correct orientation of absolute constellation. This loss is not too great for the analyzer.

Let's look, what results will bring not precise sampling rate. As minimum - the triangle will slide concerning to marker in this or that side, that automatically means that at symbol-by-symbol moving, there is almost no chance to stay on same LU. It pulls behind itself complete chaos in absolute angles, in this case, we cannot speak about any stable constellation. Also depending on speed of moving of the triangle, there can be order distortions in relative angles. There also can be different problems at the channel changing.

Let's check it up. We will change sampling rate on 1 Hz.

As it was anticipated, there is complete chaos in absolute angles. The constellation is not simply developed, it permanently turns around. In relative angles we have something looks like an order, but, at the big errors there also will be problems, with one difference from absolute angles, the constellation will not turn around constantly. At more serious changing of sampling rate, we observe more bright problems.

Let's watch what will give shift by on frequency in 0.1 Hz.

Everything will be same, but sensitivity to shift will become stronger, then to changing of sampling rate.

We will not bring examples, what will happen at shift of the signal by frequency and not correct sampling rate at same time, it is obvious that very serious problems will appear. The purpose of all this - is to show level of sensitivity of OFDM signals to these parameters.

And here it is best time to remember, in what conditions, we are situated, when we have got record of really unknown OFDM signal. Generally, we do not know anything:

1) neither the sampling rate of creation of the signal

2) nor sampling rate of the record

3) we also don't know exact frequency of signal and etc.

As we saw signal's shift only in 0.1 Hz, practically disorganizes an absolute constellation. It means, that without auto regulation systems, chances to get exact parameters of modulation are extremely not great. But there is one more problem that is : to make the self tuning system work, it is necessary to know what exact values it is necessary to support. As far as it is impossible to receive exact parameters, as in general nothing is known exactly.:) The vicious circle. This is the main complexity of OFDM analysis, in difference from demodulation, when we have the signal with completely known parameters.

Really everything is so bad? To tell the truth, all is not too good, and at this moment all we have - is the possibility to observe convincingly enough, only relative constellations, what it gives? Unfortunately nothing very great. Even having good relative constellation, without accurate absolute constellation, it is not possible to guarantee neither a modulation mode in the channel, nor value of clock frequency, neither accuracy of position of a signal on frequency, nor an exact rating of a grid of channels. All it will be: something, somewhere, in a range of something.

Why the relative constellation, does not allow to define manipulation parameters precisely? The matter is that, for example, within the limits of relative manipulation pi/4 DQPSK, it is possible, and very often it used to be done, that both PSK-2 and PSK-4 are used. And there are two variants of PSK-2, with different orientation concerning axes. Nothing prevents to use relative manipulation 3*pi/8 DPSK-8, and it is used often. This sort of relative manipulation, has in it's arsenal, even more variants and types. Generally, there is no possibility to tell precisely, only by the look of relative constellation, if it is really relative manipulation or absolute is used.

Random phase shifts in the channels are not limited, and they very easily can create illusion of obvious and very strong constellation in absolute angles.

Is it possible to prove that in this channel is not absolute PSK-4 or QPSK, and all the same pi/4 DQPSK, while the triangle is not sliding at symbol-by-symbol moving, its peak positive and LU size is even? But it is possible to make convincing absolute constellation almost in any channel.

Basically, it is possible to guarantee something only on ideal, or qualitative records yet. Thus, it is necessary concern results, received in the current version of OFDM module carefully enough.

The problem is very hard and interesting; we are planning to go further with our developments in this direction

SA: work with OFDM module, FFT spectrum. Tutorial part II.

OFDM module, FFT spectrum. Tutorial part II.

Let's consider new abilities of SA OFDM module in version 6.1.0.3.

In the description of the previous version and in the first part of OFDM module tutorial, we have mentioned "the magic triangle", and have defined, that detection of this triangle says, that the analyzed signal belongs to OFDM class with CP. We have also concerned the bases of OFDM creation principles, and we had also have defined, that the triangle is closely linked with the transferred OFDM symbol. Let's go further, Let's take a view on the triangle more attentively.

For start we will consider schematically structure of the magic triangle, and we will try to understand, why only triangle shape is the right sign and What is so good in it? As i was already spoken, the magic triangle - it is known result of correlation of two equal rectangles, but nevertheless, we will look hardly more deeply on this triangle. Here seven is(conditional) main steps of results of calculation of correlation, we assume that LS and LG are received precisely.

It is perfectly visible, that the triangle's peak precisely points on an absolute coincidence of controll LS and LS of the signal. So It is perfectly visible that the triangle left-hand side "tells" us: that LU of the controll window window of LS, has completely entered into LS of the signal(It is very importent momemnt). Increasing of the amplitudes (rising) of the left-hand side of the triangle shows to us that: the controll LU is closer and closer to it's "native position" in LS.

Right side of the triangle says that: the controll LU, does not get any more completely in the signal's LS, and it goes away further and further, thereupon right side becomes not valuble for analysis. It is impoertent to to understand why the left side is good for analysis , and right is not good. We do not want that the user thoughtlessly would place the marker on "the good side" without understanding why it should be so and what hiddens behind it.

Ок, let's look on CP (LG), what does CP give?

CP increases length of the symbol, by so much countings, how many for CP is taken. What in general it means? As CP it is a copy of a part of the end of OFDM symbol, CP possesses very important property, it "is fastened" in the beginning of the symbol precisely in the phase. Here follows awesome conclusion:

The quanitity of correct LU values is not just one in the symbol with CP.

Quanitity of the correct LU = LG+1.

More visually it looks so:

It allows us to use LU freely enough at the analysis, because any LU, which we receive on "the good" side of the triangle, is basically correct.

Let's move to practice now. I will only mark that, for getting quantity of channeles and their amplitudes, all LU are equal. We will check up everything, as well as it is necessary, on an ideal signal. Let's synthesise for example such test signal.

Everything, what has been told earlier, is approved.

Move the specified slider and be convinced that "the good side" is really good, and that it's lengh takes precisely LG size, and that on this side all channels, which are entering into LU have stable amplitude and location.

Certainly you will notice that the real signals, behave a bit differently than an ideal ones, but you will also notice that the negative triangle does not promise anything good, and that it is useless to search for anything on "the bad side of triangle", because there simply nothing to search for. You will see, that, in general, all OFDM signals with CP submit to the common laws, considered by us that. Thus as soon as the marker leaves "the good side", FFT spectrum starts to behave strange, unpredictable etc.

Let's consider some practical nuances:

Please Pay attention, on the field LU (FFT Size) = X, where is X - os the FFY block sizeFT, or size of LU in countings. On real signals, X can be any. Actually, only the even size can be considered as the correct. Odd size of LU says that, sampling rate, or signal's shift by frequency, or all that have together led to the fact, that LU precisely lays down on odd quantity of countings of sampling rate. It is not forbidden, but it is not correct. Althogh, even in this case, the program works, as we use FFT algorithm working with any quantity of countings.

Why the yellow marker sometimes is a one pixel thick, and sometimes it is rather wide bar? Here all is very simple:

The size of LS is not limited formally, there can be signals both with LS=20 and with LS=2000, and for more comfortable observation of "the magic triangle", the map is scaled, and sometimes, there are 20-30 or more of countings in one pixel, in this case, then the marker is a thin line, and sometimes one counting is expanded on several pixels, and then the marker is wide.

You can consider the results of spacing and speed of manipulation as correct or atleast very close to real ones only, in case when:

1 - your triangle is motionless at symbol-by-symbol moving,

2 - LU is even,

3 - peak is positive

Otherwise it is necessary to speak about conditional enough accuracy.

Actually, you will notice that OFDM signals, allow rough enough inaccuracies. The very good spectra can be seen even at the big errors, moreover, it is also possible to receive the quite good constellations in the channels, but it concerns only to relative sorts of manipulation. The absolute constellations in channels, such as QAM, demand very serious measures of bringing on parametres of a signal to true ones. But this is already future...for now I suggest to be mastered with this tool SA OFDM module, this tool allows to do very many things, for example, like this:

It is DAB signal. FFT spectrum of this signal do not fit into the mapping window of the module on my screen monitor:) You do not have chances to receive exact pricese parametres of this signal by another way. SA allows to get pricese parameters.

Good luck~

Signals Analyzer: SA - OFDM module detailed tutorial. Part I.

SA - OFDM module detailed tutorial. Part I.

This tutorial is intented to help with solving difficult enough tasks of OFDM analysis.

The purpose of this tutorial - is to show what is possible to learn/understand/define with the help of current implementation of SA OFDM module and small "magic triangle":).

Click here to read full OFDM module SA tutorial by MSM Group.

From this SA OFDM module tutroial you will know:

• how to define the magic OFDM triangle
• how to recognize the right one triangle, in case, when there are several triangles in the signal
• when triangle can be negative and what does it mean
• what the correct "magic triangle" should look like
• specifics of "behavour" of the correct "magic OFDM triangle"
• and more interesting and usefull features for effective analysis of OFDM signals with help of SA OFDM module.

Soon the second part of OFDM module tutorial will appear.

Yours sincerely, Maria and MSM Group.

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!

Analysis of the real Chinese Serial Modem signal.

The signals analysis. Practical approach.

The real signal 7970.wav.

It is always necessary to spent estimation of the current record's quality before the analysis of the signal. It is very essential and important step. This step, in many cases, allows to avoid useless

work with problematical records as: the records with overloads, with the distortion of amplitudes, compressions and etc. There is lot of information about records quality, but as practice, the very small amount of people take this information into attention.

In our case, any of specific problems are not observed. The signal is "live" and it "breathes", the noise level is small enough, that allows to hope for the successful analysis. The best fragments by

the spectrum are the first and the third. The second and the fourth fragments have the visible selective distortions, althoguht it is the not the reason for denial of 2 and 4 fragments, but we are choosing the best fragments. By the first look, this signal seems like founded OFDM. The typical mistake in such cases, is the orientation on the searches of the signal's parametres as OFDM, that is the other versions are not even considered. It is the mistake in the sense, that even if any disparities will be detected, it will be very hard to stop consider the signal as OFDM. All the attention will be paid to signs in favour of the OFDM version, and the signs, which are not in favour of this version, most likely will be recognised as accidental and ignored. As I always say, even if
the signal seems very "familiar" or "clear" the approach to it should be always standard and same as to absolutely unfamiliar and unknown signal, to which all arsenal of knowledge and abilities is
applied. And only then, having gathered the various data, it is possible to do conclusions and to check all the versions, co-ordinating the results, received earlier. Lets gather, without going deep, the data in favour of OFDM.

The spectrum's sort/look on the sonogram, especially in the first part of the signal is very similar to OFDM, it is possible to distinguish "channels" and "pilots-tones". The second part is lesser
similar to OFDM, but nevertheless is does create the strong enough impression of the block-channel transmission, and the "pilots-tones" between the blocks. ACF is bad and does not give the clear answer, besides, it is visible on the waveform, that the signal "is slightly beaten" by the impulse interferences. So it is not clear what ACF is that. The graphical spectrum also does not give any special pluses in favour of OFDM, the whole spectrum has not clear ejections through each ~50 Hz, and it is hard to to say is that the result of creation of the signal or something else.
In that way, there is no any forcible arguments in OFDM favour, except the first impression. The situation with "pilots-tones" brings even more suspicions: the pilot-tone, even in OFDM without CP, should be located in relatively pure space. In this signal, we hardly can recognise that condition, but ofcourse it is possible to recognize if You have great desire to believe that the first OFDM
impression is correct, and if You ignore all the disparities, which are not in OFDM favour.

Lets take envelope of the signal.

There is bright enough and obvious line on the position of expected line of the clock frequency. That line can say that the signal is already not OFDM, but FSK, PSK or QAM. The FSK is denied very fast
after using of Phase/frequency detector. But to define is the signal is PSK or QAM is problemcaticaly enoguh. Methods allowing to detect QAM, in current SA version do not exist, whether I'm also not
assured if these methods are exist in general. It is possible to define QAM or PSK on the signal's constellation, but it assumes the absolute high quality of the signal's record, and knowledge of the
carrier frequency of the signal.
It is not possible to receive the carrier frequency on this signal assured, because the signal has distortions. SA allows to restore the signal, by the clock frequency, from supposition that it is PSK.
That is, the semi-automatic corrector, in AM mode, attempts to restore the signal being orinted not on the concrete PSK order, but on the signal's belonging to PSK class basically, and also oriented on value of the clock frequency. It is not such trivial task, it also does work far not in all cases, but this only thing that we have. To check this version, I have taken the third fragment.

The work with the semi-automatic corrector, was described earlier, both in the program's Help and in other articles, so i won't consider the work of the semi-automatic corrector in the detals. I will result screenshots after attempts of restoring the signal by the semi-autmatic corrector. Here is also the video-clip, which shows the process course of how semi-mode corrector works with this signal.

Literally after four-five passeges of the semi-automatic corrector in AM mode, the classical picture is appeared in the eighth degree. After getting of the classical picture, it is possible both to
continue correction in AM mode, and to switch into X^N mode, or to combine both modes. This is the deal of technique results are usually reached very fast.

The question is: maybe it is just the fortuity or the comdination of incredible coincidences, and the corrector has distorted the signal into PSK? Theoretically it is possible. But in practice, it is very
improbable, athough sometimes it happens. For detection of such cases, it is necessary, periodically to inspect/controll waveform of the signal in the first degree: the absence of deep failures in the
signal's bar or the absence of obvious distortion of the waveform, atleast guarantee the absence of obvious distortions of the signal, unless guarantee 100% total accuracy of the corrector's work.

It is necessary to save the signal and to compare it with initial signal, essential differences should not be present. Ofcourse after the semi-automatic corrector's work the signal will be another, with
more correct spectrum, with its much more regular allocation. But the signal after corrector's work should not be the absolutely another signal, the main features and structure should stay same.

Good luck!

The author of this article is SergUA6
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