Examples of using MFSK demodulator in SA v 6.2.4.2

 Examples of using MFSK demodulator 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. 

The full version of this guide-article you may read here.

SA update to version v 6.2.3.8: Universal MFSK demodulator

SA update to version v 6.2.3.8

In this update, the pilot version of the general-purpose/universal demodulator MFSK is realized.





The demodulator supports to 256 levels (frequencies) of various MFSK signals. As an example: obtaining of a bit stream from the records Packet AX.25 and APCO-25 it is shown on the picture above. As FSK-2 it is special case of MFSK, the current extension of the module doesn't influence the previous possibilities, but only expands them.


Please pay attention on the allocation of levels of demodulation. The first and last levels, aren't restricted by the markers! Their area is stretched behind their limits, as it is shown below.

The bit stream can be presented in two variants.

The first variant is the symbol representation of levels recoded by default. In this case, the internal map of codings is used. 32 characters are supported standardly. It is favourable for using for FSK-2, MFSK-4,8,16 etc., that is, for rather few-channeled MFSK modes.

The second - obtaining/recieveing of the stream in the form of HEX-byte. Bytes in this case are partitioned/devided by the symbol-separator "x" (the Latin character "X" on the lower register).

As, the bit stream implies further processing anyway, we have refused an inverse mode. There is no big sense in an inverse mode, as an inverse can be received in any exterior viewer. Besides, we are planning to create our own special viewer of a bit streams.

Below you may view the practical example of operation of general-purpose/universal MFSK demodulator on the signal South African Navy.

Good luck!