Thor
A relative of DominoEX with added error correction.
What does it sound like?
Similar to DominoEX: flowing, stepping tones.
12-second example. A clean example made with the free fldigi program (Thor 4); signals on the air usually sound noisier.
Who uses it?
Amateur radio operators.
Where and when can I hear it?
Various ham frequencies.
The science
Thor keeps DominoEX's 18-tone incremental frequency keying, where information rides on the step between tones, and adds full-time error correction taken from MFSK16: a convolutional code with interleaving, decoded by a Viterbi decoder. Speeds range from about 2 tones per second (Thor Micro, 53 Hz wide) up to about 100, with Thor16 at 15.625 tones per second, about 355 to 420 Hz wide depending on how fldigi measures it. Each transmission starts with a distinctive double rising tone that clears the receiver's decoder.
Why use it?
fldigi describes it as particularly well suited to atmospheric static noise, and its tone-difference coding keeps DominoEX's tolerance of poor tuning. The DominoEX designers note the trade-off: the error correction did not add greatly to performance and costs some of DominoEX's quick turnaround. It was developed specifically for ARQ transfers, in which the receiving station automatically asks for a resend of anything that arrives damaged, and fldigi's version can also send small images.
Lore
ZL1BPU's pages credit Thor to Dave Freese, W1HKJ, author of fldigi, following earlier work by Patrick, F6CTE, who added error correction to DominoEX. Its images include "avatars", small pictures tied to a station's call sign, and fldigi's default avatar is the Tux logo, the Linux penguin.
Easily confused with
- DominoEX: DominoEX's error correction is optional; Thor's is always on