четверг, 15 октября 2009 г.

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!