|What is so
good about Feld Hell?
The oldest keyboard text communications
protocol is now one of the newest ham radio
modes! The hellschreiber method was used
over landline for many years before its
adaption to radio waves. This simple method
has one major advantage over all other HF
keyboard modes... The advantage comes from
the fact that it is NOT a true digital mode
in the way that modes like RTTY, PSK31 and
Pactor are. With Hell modes the text
characters are not decoded by the computer
program. For this reason, you will hear
hellschreiber described as a "fuzzy mode".
Hell text is "painted" to the screen as the
Hell tone is being received through the
sound card. To receive a Feld Hell signal,
the computer program sets up the sound card
to use DSP techniques for detecting the
signal and places the output on a short
vertically scanning line that is moving
horizontally across the screen. This action
produces a single line of text in a marque
fashion that gets wrapped around to
eventually create a full screen of text.
Really simple! The computer never has to
decide (decode) the characters and so no
missed characters or wrong characters will
ever be sent to the screen! To send Hell
characters, the computer program uses the
sound card to produce the audio signal to
modulate the transmitter in the same way
that other sound card modes are transmitted.
For Feld Hell, it is an on/off single tone
the same as used for MCW. Each tone burst is
conditioned by the DSP to have the correct
shape that will not cause harmonics and "clicks"
to be produced by the radio's modulator. A
properly adjusted Feld Hell input level will
produce a bandwidth of no more than 75 Hz.
Over driven levels will appear as wider
signals on the waterfall display.
With Hell modes, the only time that a
received character appears wrong on the
screen is when it is typed wrong at the
other end. The only time when a character or
word is not readable on the screen is when
radio propagation is so bad that not even
DSP techniques can pull it out of the mud!
This occurs at signal levels considerably
lower than those tolerated by all other
modes. The weakest link in decoding Hell
characters will be the operators ability
distinguish letters under noisy conditions.
Another advantage of Feld Hell mode over
most others is the ability to print readable
text under conditions of polar phase shift.
A severely phase shifted signal will print a
shifted character, but it can still be read
on the screen. Each Hell character is sent
on a double line, so that if one character
is shifted off the marque, the other will
still be visible. Another nice feature of
Feld Hell is that the RF power output cycle
is less than 50% during TX, saving energy.
One nice feature that feld hell has in
common with PSK31 is a very narrow bandwidth
used by the signal (about the same as for CW).
The end result is the most reliable keyboard
communications achievable on HF ham radio.
So why isn't everyone using Hellschreiber
How does Feld Hell compare with PSK31?
- The hardware setup and cabling is exactly
- Good freeware and shareware software is
available for both.
- Tuning in a hellschreiber signal is easier
- Hellschreiber is a little slower for
- No cut-n-paste from the receive screen
- You can chose the text font for sending
- Weak signals have better readabilty with
PSK31 is a true digital mode and for
some people that makes it a "sexier" mode
than Hellschreiber. Hell modes are more
closely related to CW than to other digital
mode. With CW you use your ears and for Hell
modes your eyes. Having both fuzzy and
digital modes available on the computer desk
top has been a good strategy for me. The
Hellschreiber frequencies are next to the
PSK31 frequencies on most ham bands, so they
are easy to mix. As more PSK31 ops discover
how nicely the two operating modes
compliment each other, we will see more
the other Hellschreiber modes?
The very popular Hellschreiber freeware
IZ8BLY and the Shareware program
UT2UZ have other experimental Hell
modes included. Of these, there are two
modes besides the traditional Feld Hell mode
that hams have found to be useful and are
currently using. PSK HELL and FM HELL modes
both come in a 105 baud and 245 baud rate.
With these modes, the ON/OFF keying needed
to paint the Hell characters across the
marque are sent by shifting the phase of two
tones (PSK Hell) or by shifting the
frequency of one tone (FM Hell). The faster
baud rate for both modes does not increase
text speed, but it does increase resolution,
producing a sharper font. Both modes have a
100% duty cycle during transmit, but the
additional power will produce a less noisy
background, making the text easier to read.
With either of these modes, it is fun to see
the font flow across the screen like a
video, as apposed to computer type set. When
your eyes get tired of reading computer
text, try Hell modes!