Generic MFSK Decoder

 

General description

The Generic multi-tone FSK (MFSK) decoder is a universal decoder for MFSK transmissions. It decodes MFSK signals from 10 baud/tone to 2500 baud/tone. It supports the decoding up to 64 MFSK tones. In most cases it is used together with the SkySweeper bit analyzing tool, which provides the synchronizing and character display functions. Generic MFSK does not support automatic frequency locking. The decoder frequency (=lowest tone frequency) must be set either by double clicking the left mouse button or by setting the default first tone parameter in the ‘Config’ dialog. The bolded blue bar in the decoder’s spectrum display indicates the frequency of the lowest MFSK tone.

 

SkySweeper supports both FFT and waterfall display modes for decoder tuning. The Decoder Spectrum Dialog chapter gives more information about spectrum display options.

 

Configuration

Pressing the ‘Config’ button opens the following Configuration dialog box.

 

 

 

 

Parameters

 

Pulse Length

The MFSK tone length in milliseconds can be set here. If the mode is already known, the tone length is easy to set (for example COQUELET-13 has pulse length of 50 ms or 75 ms). If the pulse length is not known, it has to be analyzed for example by using the waterfall (spectrogram) or the HFFT display.

 

Baud Rate

The MFSK baud rate can be set here.

 

Default first tone

This is the default frequency for the first tone. (for COQUELET-13 this is 812 Hz)

 

Number of tones

Number of tones in MFSK transmission.

 

Tone Spacing

Tone spacing in MFSK transmission.

 

2 Simul(taneous) Tones

If this is active, the Generic MFSK decoder detects two active tones (instead of one) at the same time.

 

Upper Tone First

If this is active, the bits corresponding to the upper tone are printed first. This is active only when ‘2 Simul Tones’ is selected.

 

Set default bits

When this is pressed the tone bit values are set to their default values.

 

Tone bit table

In the lower part of the configuration dialog, there is a tone bit table. The bits corresponding to each tone can be set here.

 

Print Format

The generic decoder print format can be changed by pressing the right mouse button over the text area window and selecting Properties from the pop-up menu. The Properties command opens the Bit Display Configuration Dialog

 

FFT

The FFT button opens and closes the power spectrum window. You can, for example, close the power spectrum window when the decoder has been locked onto the correct frequency in order to get more space for the text window.

 

Save

The Save button opens the log file control dialog, which is used to open or close a log file. The detector text window can also be saved into a file or sent into a socket.

 

Lock

The Lock button locks or unlocks the decoder frequency. The decoders have the ‘automatic frequency tracking’ feature. Push the Lock button when you want to lock the decoder onto a selected frequency. Push the Unlock button when you want to release the frequency locking.

 

Reset

The ‘Reset’ button resets the decoder and clears the text window.