FELD
HELL
Traduction anglaise.
FM Hell is a Hellschreiber mode. The Hellschreiber modes FELD HELL, PSK HELL, FM HELL and HELL 80 are
graphical modes where characters are drawn and the interpretation done by the
user. For FELD HELL, the transmission is done by On-Off keying (OOK) as in CW,
by BPSK for PSK HELL and by AFSK in HELL 80 and FM HELL (MSK in fact).
This mode is included into the software MULTIPSK by Patrick F6CTE, there is the description of this mode and its
variants as well as the specifications coming from his software :
Click on the copy of the screen in order to
listen to the corresponding audio
signal.
Generalities: Feld Hell is a Hellschreiber mode. All Hellschreiber modes are "Fuzzy" modes. The rules to be "Fuzzy" are:
- the transmitter uses no coding,
- the receiver does not decide when data is present,
- the receiver does not decide what data is present.
These modes are only human readable. They cannot be read by computers
unless sophiticated neural system are used. In fact, hypothesis that
human eye/brain character recognition in its context was better than a
computer could do,
Created by : Rudolph Hell in 1929
Description :
Baud rate : 245 bauds but, in fact, it is a pseudo-122.5 bauds (one "pixel" is 8.163 ms long)
Reading direction : column by column, from down to up and from left to right,
Matrix : height: 7 pixels et width: 7 pixels…so a total of 49 pixels per character
Speed : 25 wpm
Modulation : On-Off keying of an audio tone
Reception mode : indifferent (USB or LSB) but in general 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 : raised cosine profile
Bandwidth : about 300 Hz,
Synchronization : no need, each column is displayed vertically 2 times (but transmitted once)
Pmean/Ppeak : 0.25
Lowest S/N : - 12 dB
Note:
pieces of information about Hellschreiber modes can be found on the WEB
site of ZL1BPU (Murray Greenman). Pascal F1ULT make a french
translation of ZL1BPU's site on http://f1ult.free.fr.
Recommanded
frequencies for FELD HELL (USB)
Valid also for PSK HELL, FM HELL and HELL 80.
3580, 7035, 10135, 14063, 21063 and
28063 KHz
