Kantronics KPC-4 - Page 47

RTTY and ASCII Modes
KAM only
RTTY Theory
RTTY is a 5 level (5 bit) Baudot code, which limits the number of possible characters
to 32. This obviously does not provide enough combinations for all 26 letters of
the alphabet and the numerals and punctuation. Therefore, in order to allow more
combinations, two special characters have been reserved as a FIGURES shift and
LETTERS shift. When you first enter the RTTY Mode, the system is in the LETTERS
shift, thus allowing normal alphabetic characters to be typed. When you type any
numbers or punctuation, the KAM automatically inserts a FIGURES shift prior to
sending the character. One FIGURES shift is sent prior to the beginning of a string
of numbers, but if a space is typed, a new figures shift will be required. You may
manually insert a FIGURES shift by typing a Ctrl-N or a LETTERS shift by typing
a Ctrl-L. If this is done, the KAM will not insert the FIGURES shift for you, for that
sequence of numbers.
The standard mechanical teletype machine always "un-shifted" when it received a
space character, thus any numerals or punctuation immediately following a space will
require a FIGURES shift to insure that the receiving machine is in the FIGURES
mode. The KAM simulates this un-shifting based on the setting of the USOS
command.
When operating in RTTY, standard procedure is to transmit approximately one line of.
RYs
prior
to
actually
typing
your
message.
This
allows
the
receiving
station
time
to
properly
tune
his
station,
and
adjust
his
receiving
equipment.
This
was
particularly
true
with
the
older
mechanical
units,
but
has
carried
over
into
today's
computer
terminal
RTTY
operation.
A
typical
sequence,
then,
for
calling
CQ
might
look
like
this:
RYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRY
CQ
CQ
CQ
DE
WK5M
WK5M
WK5M
CQ CQ CQ DE WK5M WK5M WK5M
CQ CQ CQ DE WK5M WK5M WK5M KKK
The
RY
has
been
used
for
the
synchronizing
and
testing
purposes
because
in
the
5
level
Baudot
code,
this
represents
a
complete
reversal
of
the
bit
pattern,
therefore
the
receiving
mechanical
machine
had
to
completely
reverse
all
levers
and
gears
within
the
time
frame
of
one
character.
It
was
felt
that
if
the
machine
could
do
a
complete
reversal
like
this,
it
could
copy
any
other
combination
without
problem.
i
RTTY
is
transmitted
using
FSK
(Frequency
Shift
Keying)
in
which
the
two
possible
conditions
for
each
bit
of
data
are
sent
as
two
distinct
frequencies.
These
are
called
MARK
and
SPACE
and
the
difference
between
these
two
frequencies
is
called
the
SHIFT.
Most
amateur
RTTY
is
transmitted
with
a
170
Hz
shift,
but
other
common
shifts
used
are
425
Hz
and
850
Hz.
With
FSK,
the
frequencies
are
generated
by
changing
the
actual
carrier
frequency
of
the
transmitter.
Another
method
of
transmitting
RTTY
is
to
generate
the
tone
within
a
piece
of
equipment,
and
then
modulate
the
carrier
with
the
tones.
This
is
called
AFSK
(Audio
Frequency
Shift
Keying).
The
KAM
supports
both
methods
of
transmitting
RTTY
and
ASCII
signals
as
well
as
all
three
of
the
standard
shifts.
In
addition,
the
KAM
can
use
non-standard
shifts
by
selecting
MODEM
SHIFT
and
setting
your
own
choice
of
MARK
and
SPACE
tones.
©
Copyright
1989,
Kantronics,
Inc.
All
Rights
Reserved.
P
Duplication
of
this manual
or
the
firmware
without
Version 2.85
permission
of
Kantronics,
Inc.
is
prohibited.
Operations
Manual