General description
MFSK16 is based on multi-tone FSK modulation and also utilizes the most modern FEC (Forward Error Correction) techniques as well as interleaving. MFSK16 provides 31 WPM text throughput with FEC and 61 WPM with no FEC. SkySweeper uses soft bit Viterbi decoding in FEC mode. SkySweeper supports also 2MFSK16 (63WPM) and 4MFSK16(125 WPM) modes.
The decoder searches the MFSK16 transmission within the given frequency boundaries. Also you can set the first MFSK16 frequency by double clicking the mouse on the required frequency position. The value of the first MFSK16 frequency is shown on the screen. When an MFSK16 transmission has been detected in the given range, the decoder will then lock itself to that frequency. When locked, the decoder draws a bold blue line on the spectrum display at the currently locked frequency (the blue line is drawn on the 1st tone frequency). If the decoder is not locked, then the blue line is not shown as bold. When the frequency is locked, the decoder starts to estimate the keying parameters of the transmission. When all the parameters have been estimated, then the decoder starts to print characters on the screen. In the locked state, the carrier frequencies are automatically monitored within the given frequency boundaries and if the carrier frequency changes, then the decoder moves to a new frequency. If 'Lock' is pressed in the user interface, then the decoder will not automatically change its frequency. ‘Reset’ resets the decoder. Received text can be saved using ‘Save’. The parameters can be modified by pressing the ‘Config’ button. Note that you can install several decoders in one configuration, if required.
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:
Tone scan area
The scanned frequency range is given with two values - ‘low’ and ‘high’. The MFSK16 transmission is searched for only within this frequency window.
FEC
If FEC is selected, the Forward Error Correction is used. This means that interleaving and convolution coding is used to protect the data. When FEC is selected, the text throughput will be dropped by 50%.
Mode
The used mode is selected here. MFSK16 is a standard MFSK16 transmission. 2MFSK16 is double speed version and 4MFSK16 is four times faster version of the standard mode.
FFT
The ‘FFT’ button opens and closes the power spectrum window. You can, for example, close the power spectrum window when the decoder has locked into 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. 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 frequency locking.
Reset
The ‘Reset’ button resets the decoder and clears the text window.
