FM Hell Modes
Createad by : Nino Porcino (IZ8BLY) and Murray Greenman (ZL1BPU)
Baud rate : 105 or 245
Matrix : - for FM HELL 105 bauds…height: 6 pixels and width: 7 pixels
- for FM HELL 245 bauds…height: 7 pixels and width: 14 pixels
Speed : 25 wpm
Modulation : MSK with a "minimum" shift between tones of 122.5 Hz (at 245 bauds). The white is at the upper frequency and the black at the lower one.
Receive mode : USB
Character set : all ASCII printable characters except small letters, carriage return (+ line feed) and error correction character. The used font (FeldHell) is derived from the font of G3PLX (Peter Martinez),
Shape of pulse : rectangular
Bandwidth : about 130 Hz for 105 bauds and 300 Hz for 245 bauds,
Synchronization : no need, each column is displayed vertically 2 times (but transmitted once)
Pmean/Ppeak : 1
Lowest S/N : - 10 dB for the 245 bauds mode
Note: the Multipsk "105 bauds" is not a "105 bauds" as described previously. It is, in fact, a mode similar to the 245 bauds and using the same characters (7 x 14 pixels). The difference lies in the frequency variation which is not the MSK one (i.e. +/- 61,25 Hz) but it is equal to 61,25*105/245 Hz. When receiving, it comes to the same (modes are compatible). In the other hand, this solution has the advantage to be able to use 7x14 pixels characters and so to keep on with a good definition.
Others pieces of information about Hellschreiber modes can be found on the WEB site of ZL1BPU (Murray Greenman) .