User manual

Teletype (TTY) systems by devising a 7-level code that, for valid
characters, provides a constant ratio of four binary ones to three
binary zeroes (4:3) in the code pattern. Such a code has the ability
to determine whether received data is valid or not. This simple
code then allows for a primitive means for data error control in
either forward error control (FEC) or automatic repeat request
(ARQ) modes.
When in FEC mode, each data character is coded in the appropri-
ate 7-level code, then multiply sent at different times, so to enable
time diversity detection. For ARQ, five characters are grouped
together to form a 21-bit data packet which is sent in a strictly
timed synchronized sequence.
The SG-7200 AMTOR implementation offers a modernized ver-
sion of the original AMTOR implementation, adding several inno-
vative features that have evolved since the introduction and accep-
tance of AMTOR.
5.1.3 Pactor I
Pactor I is a recent development of German amateurs Hans-Peter
Helfert, DL6MAA, and Ulrich Strate, DF4KV. It combines the
most-desirable features of AMTOR and HF Packet radio. This pro-
tocol is superior to both these. Not only does it guarantee deliver-
ing error-free data, but also does it much more efficiently. The pro-
tocol is adaptive between 100 and 200 baud and does use of
Huffman data compression to further improve efficiency. As for
AMTOR, there are two basic modes FEC and ARQ.
5.1.4 Maritime Mobile Marine CCIR 476/625
The SG-7200 firmware includes a dedicated CCIR 476/625 imple-
mentation that contains several features not used in Amateur Radio
service. This implementation conforms fully with CCIR recom-
mendations 476, 625, and 492. This includes ARQ, FEC, NAV-
TEX, and SELFEC modes.
The SG-7200 can function in an automatic marine radio; traffic-
handling environment by automatic reception, recognition and
traffic forwarding according to "free channel" signal formats
broadcasts. This comprehensive implementation allows the SG-
7200 to operate equally well aboard vessels sailing the oceans, or
part of shored-based operations.
SG-7200 CCIR 476/625 software uses a convention where the
mark tone is the lower of the mark/space set. This requires that
upper-sideband (USB) mode to be selected on a transceiver. When
using this convention, the front panel LED display will correctly
indicate mark and space signals. Transmission will also emit the
7
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