xfhell is a GTK+ application for the "fuzzy" digital communication mode known as Hellschreiber. xfhell has several different built-in fonts in Adobe BDF format, including a font set for Greek, and a special "short" font set that is 12 pixels high instead of the standard 14 of the original Hell fonts. Using this font set would make xfhell incompatible with other Hellschreiber programs, but the short fonts speed up operation and avoid wasted bandwidth, inherent in the original Hellschreiber design (an unavoidable problem of the original mechanical implementation of the mode). xfhell also has selectable lower baud rate operation (down to 7.6 Bd), which again make it incompatible with other Hellschreiber programs, but the lower speeds (especially combined with the 12-pixel fonts) would make this mode even more efficient and effective.

Another distinguishing characteristic of xfhell is its ability to compensate for slight differences in the clock frequency of sound cards, which produce the characteristic skew of decoded text, requiring double-row printing in order to make it legible. Hence xfhell prints received text on a single row, continuously compensating for clock skew and propagation path effects. This feature works well when capital letters are in use so that with lower-case letters, the printed text tends to wonder up-down in the screen - please avoid lower case letters, they are hard to read anyway!

xfhell has built-in CAT control for the FT847 and FT857 transceivers and a QSO logging facility similar to xpsk31. It also has a FFT-derived waterfall display of the incoming signal, with the ability to detect maximum signal level and tune the transceiver, via CAT, to the appropriate carrier frequency by clicking near the signal trace.

Authors:
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Neoklis Kyriazis, 5B4AZ <n5b4az (at) yahoo (dot) com>