FLDIGI Users Manual  3.21

Thor is a new forward error correcting incremental frequency shift keyed communications mode. It was developed specifically to meet the needs of ARQ transfers in the HF spectrum. It is particularly well suited under conditions of atmospheric static noise. Thor borrows from two current modem technologies, MFSK and DominoEX.

Thor emits a distinctive double rising tone sequence at the beginning of each transmission. It is used to flush the receive decoder and also provides a visual and audible clue to its being used.

The modem code for Thor uses a wide band multiple frequency detector that can lock on and detect the incoming signal even when badly mistuned. Frequency domain oversampling is used to allow proper tone detection without the need for AFC. The AFC control does not alter the decoder in any way.

The waterfall and digiscope will appear as:


The text displayed in the status area is the secondary text being sent by the transmitting station. When the keyboard buffer is empty the Thor modem transmits text from the secondary text buffer. Your secondary text buffer can be edited on the Thor configuration tab.

The digiscope display is similar to the DominoEX display and represents the tone pairs moving through the tone filters. You can also use an alternate digiscope display (left click on the digiscope display area).


In this display mode the red line represents the center of the multiple tone bins that are in the detector. The dots will be blurry if the AFC is not locked on and become very distinct when AFC lock has been achieved. The tone dots will move from bottom to top (opposite the direction of the waterfall).

This is the same signal mistuned:

DominoEx Mistuned

and with the signal badly mistuned:

DominoEx Mistuned 2

Return to Top of Page
Return to Main Page