What is signals analysis? And why the signals must be analyzed?

What is signals analysis? What is it nessecary for? Why is it not possible to use decoders without analysis of the signals?

Author: SergUa6 and other MSM Group members.

We receive many letters with such questions, despite the fact, that the answers to these questions are stated in number of our articles, we have decided to make this short, but informative article. Okay, let's begin from start.

Everyone who has receiver heard not clear sounds and strange signals, and each time there is the question what is it? Only extremely small amount of people can exactly identify these signals and sounds for sure. While most number of people still suppose, that the only one way to identify the signals it is their ears. This is an absolute error.

Let's consider "analysis by ear" on the real examples and situations.

Examples of What is impossible to do by "ear-analysis":

• to distinguish OFDM with 20th channels from OFDM with 18 channels
• to hear the difference between OFDM with manipulation speed 50 and 45
• to differ PSK from QAM
• to distinguish PSK-8 from PSK-4
• to hear the difference between GFSK from MSK
• to distinguish FSK with speed 1200 from PSK with speed 1200
• to distinguish MFSK-32 from MSFSK-30
• ear can't exactly define that frequency spacing is 110 for example, instead of 100
• You can't distinguish MFSK-64 from MFSK-60 by ear

I can endlessly countine this list of the real and widespread situations ,where "ear-analysis " fails and simply doesn't work.

Ofcourse it is possible to distinguish CW from RTTY by ear, same as we can differ male and female voice and etc. But it is better to close the question about abilities of ear-analysis. With each day there are more and more digital signals and protocols are appearing, already for today there are more then thoudands types of them, and all that can't be identified and analyzed by "ear-analysis". Let's leave for ears things which are ment for them: music, speech, CW.

We were surprised by the fact that there are people, who believe in "ear-analysis", mostly that part of people believes that there are only two types of the signals: CW and RTTY. Thus, "ear-analysist" name everything what is not getting under these two cathegories as "digit" type.

The main function of the signals analysis - is exact and precise definition of parametres of a signal, such as: speed, sort of manipulation and much more. That allows to identify the signal absolutely precisely and authentically.

pic.1 Function of Signals Analysis

The picture 1 shows the purposes and the place of analysis. To us it is well-known that many people ignore the analysis basically, because they believe that decoders "will understand" and decode any signal and even unknown sound. Probably many people from those who are reading this article, got into situation when the decoder program produces random set of digits or characters. And there are no ways to understand what are the reasons for it, and how much authentic is this set of characters and digits or is it simply random trash?

I don't think that i'm opening the big secret: but all decoders work only with that type of signals, for which these decoders were specially created. In case if the signal has another parameters, like different speed, or another modulation, or any other parameteres from the expected ones, then even best decoder can't realize it's functions and don't decode anything.

Ofcourse the good decoder program has customised parametres, but how it is possible to expose/specify the parametres, if they are not defined precisely or not even known at all? And where is a guarantee, what you try to decode some correctly identified signal, instead of absolutely another?

The good analyzer will help with solution of all these problems:

• with precise definition of parametres of the signal
• with identification of the signal
• with a choice of the suitable decoder, for any signal which you have accepted/have written.

pic.2

As it is well-visible from picture 2: it is impossible to decode any sound and signal without Signals Analysis.

The analysis itself is not so hard as it may seem at first look, but it requires training and learning as any other professional or hobby sphere. It is same situation when : as soon as you learn how to read books at school - you open another interesting world, while illiterate person do not even know about existence of such world.

But if to meet the illiterate person today is uncommon thing, to meet "ear-analyst" is the very usual situation, althought "ear-analysis" is very similar to illiteracy:)

MSM Group is applying all best efforts and doing all possible and also impossible, to help everyone who wants to become engaged into signals analysis and develop their skills in that direction.

Good luck!

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
All rights reserved © http://signals.radioscanner.ru

Offline analyzers and real-time analyzers.

In the almost four years of the development of the Signals Analyzer, practically constantly we are taking part in the discussions, where most popular questions are:

- Why SA is offline signals analyzer and not the real-time?
- Why is this necessary to use Signals Analyzer while some people can define signals by ear?
- What will I have by using SA?
- There are lots of professional real-time analyzers and everything works okey in real timeanalyzators aswel?
- Why SA do not include real time analyzer and decoder? And etc etc

We have decided to reply on most popular questions, and the answers, which will be represented - are the result of long-standing practice, not just our opinion. I think you will agree that the best
answer on the question, is the fact which was admitted on practice many times.

First of all, I have to disappoint people who analyze signals by ear. I do not deny, that some people have abilities for that, but it is the absolute impasse, even when you have abilities for that.There are tens of hundreds of signals, where these people frankly give up, but they greatly are proud of the fact that they can distinguish CW of RTTY, but nevertheless they ask “why can’t I decode anything in MiX or SkySweeper?”

Our team is also still getting surprised, when people send us sonograms and ask to analyze them, or they try to analyze the sonogram by their own. The real analysis must have the object of analysis, and the object of the signals analysis – it is record of the signals first of all. In 90% of cases, we can see one stuff on the sonogram and hear completely other stuff on the record. Analyst has no interest to shadow of the signal, the record of the signal is the first thing, which is necessary.

These two aspects explain paradox: on hundreds of forums we see lots of same questions like: what is rustled yesterday? I heard grunted signal, something is hisses in my dynamics what was that?? And only small amount of people can intelligible answer what was it, who was it and etc.
The paradox is: everyone want to know details about the signal they cached, but only small number of people able to know it for real. Besides, signals analysis isn’t that terrible hard as many people think about it.

Now couple of words about real-time analysis. Don’t want to disappoint most of people, but…….today, the real-time analysis it is fiction, it does not exist in that kind of way, which most of people imagine. Of course, many developers are occupied by the real-time analysis, and our MSM team is also engaged into it. But we can’t create real-time tools, until all problems of the offline analysis will be fully solved.Surely, analysts who need fast and unclear analysis with an absolutely not accurate, not precise, not exact and not clear results, can please themselves with the illusion of the real-time analysis.

I underline, we are speaking about real true analysis, when the signal is unknown, and even, when it is not even known if it is signal or just noise. Sorting from the known signals as many programs do - this is not analysis. Especially, we can’t deny that we all need secure exact results, and get such results we can only through offline analysis.

The next question is : why SA does not include decoder, this is sooooo bad!

Well, let me explain. First of all, please, pay attention on the fact, that decoders work ONLY with
absolutely known signals. If the signal is unknown or it is shifted or it has parameters, which are
different from the expected parameters, then the decoder sharply moving in the category of the
beautiful expensive knickknack. Any of bit streams, in this case, can’t be considered seriously.
Thus, we see that the signals analysis and decoding of the signals are two completely different
categories. Analysis identifies the signal, gets parameters of it, studies it, and only after the
signal is analyzed, it can be placed into decoder. The better signal is analyzed, the better results
you will get after decoding.

Professional expensive software, mostly consist of real-time decoders, where functions of the signals analysis are declared. But in reality these functions of analysis just do not work. It is impossible to do reliable trustworthy analysis by such functions.
The overwhelming majority of people don’t want to admit it, but it does not change anything actually.


Thus, you understand, that analysis of the signals and decoding of the signals, are completely
different spheres of activities, which are going together and analyzers prepare material for decoders. And there is no other way.

So why SA? No problem, you can choose any other product, if it will give secure and reliable results as SA gives, will be more comfortable and better then SA and will be cheaper then SA.
Our MSM team has been developing and creating methods and principles of the signals analysis within 4 years, we still develop our own unique tools, which are designed specially for the practical applying, and seems like we have some success here:) SA is in constant development and evolution.

Recently there was the very interesting hypothesis that SA it is the plagiarism of Centurion. To visitors Resource (www.radioscanner.ru) it is not necessary to explain anything because the evolution of SV program (the first versions 2004-2005) into SV + (2006-2007), and after into SA (2009) occurred on eyes of many people. Monteria company really had the licence for usage of the program SV + under The COA brand, in their products. Approximately one year ago,probably a bit more, the licence was expired, the project SV + had been recognised by us as outdated and succssesfully abandoned.We decided to realise all our operating time and new ideas in the commercial project SA , and this decision was accepted. Whole mathematic had undergoned the careful analysis and full re-processing, it had allowed to increase speed of processing on the average by 30 %. Most of algorithms were realized on qualitatively another level, and today SA has not anything common with SV + and-or COA in the plan of mathematics and realisation of algorithms. The general concept is saved, becasue to us it does seem convenient enough, and the bases of this concept had been put into SV (2004-2005).


Many people write that SA free is too functional for demo version. I have to dissapoint you , it is only seems so. SA free is practically version SV + from March-April, 2007, with certainly out-of-date
solutions and the mathematics, it is having problems and inaccuracies in the analysis, and it is accessible only with the purpose of familiarization with the main ideas and principles. Eventually in the process of SA development the distance between commercial version of SA and SA free will only increase.

And in conclusion...What will You get from all that analysis stuff? All same what you have from book that you had read, from the QSO that you done, from the contact with your friends and etc.
Can You have more?Of course you can. Good analysts are on demand nowadays, this is profession. After all this is sphere, where amount of skilled, competent specialists is less then no matter where.