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Examples of using MFSK dem in SA v 6.2.4.2
In this article, we will consider examples of usage of universal MFSK demodulator in SA version v 6.2.4.2
Practically, any FSK/MFSK signal can be demodulated to a bit-stream in SA last versions. Here is, when we say "any" we mean, that there is nothing known about a signal initially. Also it is meant that necessity for obtaining/getting of the bit-stream can arise at any moment, on any signal, or any part of a signal.
The Example. The record of an unknown system in a VHW band ~900 mHz.
Step by step guide of main actions is shown below:
Step 1. Select a necessary/interesting fragment of the signal and create a copy.
Step 2. Select a necessary/interesting band of the signal and move it in a bottom.
Step 3. The Main objective of the previous step is the reduction of sampling rate to an optimal value. Initial record has sampling rate 68 mHz, and it has sampling rate for the signal, which is interesting us with the full spectrum in ~ 180-190 kHz is absolutely superfluous.
The mechanism of the abstract frequency conversion of sampling rate is built in SA, that is to us it doesn't matter which sampling rate will be specific, it is important that it would be optimal. It works as follows, and we had already wrote about it in one of updates.
In the same way works the abstract shift of a signal by frequency. It is also doesn't matter to us which position the signal occupies, but it is important that it would be in optimal position by frequency on sonogram.
Let’s come back to the signal.
Step 4. After the first frequency conversion of sampling rate, and setting suitable adjustments of the sonogram display, it is visible, that the signal occupies still smaller frequency band, which doesn't exceed 180-190 kHz and the current sampling rate ~ 11.33 Mhz is strongly overrated and also is absolutely superfluous. As in previous steps we reduce it to optimal value (~800-500 kHz) via mechanisms of signal transfer by frequency and oversampling. We will pass these steps, as they are the full copy of the previous actions.
Step 5. Attempt to get value of manipulation speed via function ADP. On this example the result is ~ 21.4 Hz, most likely it is not correct. It is obligatory to realize re-check.
Step 6. Now let’s make an obtaining of the value of speed of manipulation manually. The result is ~ 76810 Hz, it is much more real and convincing.
Step 7. After we got authentic value Br, we are calling function of the phase detector, which per se is the high-quality discriminator. The result of operation of this function is taken out in the window of review of a signal waveform for the further operation. Our purpose, I will remind, is an obtaining of a bit-stream.
The further steps come to selection of the necessary fragments in the module of the signals waveform viewer and calling of the universal MFSK demodulator.
There are three independent fragments of data transfer in the researched signal. It is well visible both at once and by results of the last action 7.
It is possible to get a bit-stream both any fragment and any part of any fragment.
The bit-stream of the first fragment:
The bit-stream of the second fragment:
The bit-stream of the third fragment:
As it is possible to see there is no any problems. Moreover, you have warranties of a correctness of a bit-stream, as you fully control the process of bit-stream getting/obtaining.
Other example. The record.
It is necessary/or we want to get a bit/symbolical stream from the selected fragment.
After the standard operations described earlier, and transfer of the fragment interesting us to MFSK module of the demodulator, actions on similar signals should be the following:
Selection of a necessary amount of frequencies and their positioning can seem difficult. Please pay attention, that in the signal not all frequencies are used, and to count them “in a forehead”/directly is impossible. Actually, all is very easy!
Set the main markers on extreme frequencies as it is shown on the picture.
Now, simply increase an amount of levels until all signal levels and additional marker lines will coincide.
Increase value of levels on one, and set the main markers in optimal positions.
Now you got the correct bit/symbol stream , as well as an amount of frequencies = 32. :-)
Basically, the main operation with the universal module of MFSK demodulator has been considered.
Certainly, there are nuances. But, in the first, it is the pilot version, and in the second, as well as any universal tool, this module (and SA fully as well) possess considerably bigger possibilities, than is described in our articles and examples. We affect only high lights, basic moments, potential possibilities and a spectrum of tasks that being solved, much more widely.
Good luck~
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| Файл создан: 04 Mar 2011 21:09, посл. исправление: 04 Mar 2011 22:31 |
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