SCS PTC-IIex, Manual

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15 Basics
The
SCS
team, in developing PACTOR-II, came up with a simple and clever answer to
these problems. The Markov compression would be limited to the 16 most common
leading characters. All other characters result in normal Huffman compression. We have
thus a hybrid of Markov and Huffman coding, that we have named "pseudo Markov
coding. The coding table remains reasonably small, and the uncommon characters can no
longer cause trouble due to their unstable probability results. In practice it has been
shown that PMC almost always produces a greater benefit compared to normal Huffman
compression.
15.4 PACTOR-II in practice
15.4.1 General points
Those experienced users of PACTOR-I should have no trouble changing to PACTOR-II,
particularly if they know the usual commands of the
SCS
controller for PACTOR
operation. Before the first try-out on the air a check should be made, using the
MYcall
command (refer to chapter 6.62 , page 63 ), to see that one's own callsign has been
correctly loaded into the PTC-IIex from the terminal program. If this should not be the
case, then put in the callsign manually using the
MYcall
command. Other than this, it is
essential that the AF output level, together with the maximum output power in FSK and
DPSK are correctly set. For this, see the information contained in the description of the
two commands
FSKAmpl
(refer to chapter 6.42 , page 55 ) and
PSKAmpl
(refer to chapter
6.73 , page 69 ). Once that has been done, then one is ready to start. The transceiver can be
tuned to say 3583.7 kHz or 14079.0 kHz, and DL2FAK called (providing the frequency is
clear). If there is PT traffic on the chosen frequency, irrespective whether PT-I or PT-II,
the PTC-IIex will automatically copy it, providing the
Listen
mode is turned on (refer
to chapter 6.49 , page 57 ). As with previous PTCs', a connect is started with
cmd:
C
CALLSIGN <Return>
At the very start of a link, the two controllers automatically agree to use the highest
common level. This functions with all known PACTOR-I equipment, as these all contain
a correct implementation of the Level-1 protocol for the initial link. At present, we know
of no PT-I implementation which does not work correctly with the automatic level setting
during the initial link-up. The user knows virtually nothing of the auto level setting
procedure and does not have to concern himself with it. In the case where a Level-II link
is set up, the appearance of the tuning indicator changes drastically in comparison to the
usual FSK tuning help.
15.4.2 The tuning indicator and tuning behavior
The tuning indicator consists of 15 LED’s, which, during Level-II operation, not only
show the quality of the received signal, but also its frequency offset. Unlike with FSK
operation, these two operations are practically independent of each other. With an error
free received DPSK signal, only the two outer LED’s should flicker. If the signal contains
noise or other interference, then some of the middle LED’s will flicker, more or less
brightly, depending on interference.
The frequency offset is shown separately with one of the 13 inner tuning indicator LED’s.
If the tuning is exactly correct, then the centered LED is permanently lit. An offset of
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