SCS P4dragon DR-7800, Installation Manual

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3.The PACTOR Modes
0
1.000
2.000
3.000
4.000
5.000
6.000
P1 P2 P3 P4
PACTOR Speeds
PACTOR Speeds
Figure 1: Comparison of the PACTOR modes
Special Features:
P4 modems provide a new FSK sync algorithm (normal PACTOR link
setup) with excellent sensitivity (-18 dB) and instant frequency offset
compensation (±280 Hz). The IRS (base station) corrects the receive
AND transmit offsets immediately after FSK synchronization. The ISS
(user system) then only must correct the residual offset (smaller than ±5
Hz) right after the FSK synchronization and thus P2-P4 connections
start up with full speed even if the initial offset was as high as ±280 Hz!
Even the first FSK-ACK/NACK signal from the IRS appears on the
“correct” frequency. This feature is especially valuable on higher HF
bands. A TRX frequency accuracy of 10 ppm already yields a deviation
of ±140 Hz on the 20 m band.
3.4 PACTOR-IP-Bridge (
future feature of the DR7800
)
The PACTOR-IP-Bridge (PIB) is a Network Integration Protocol developed by
SCS
. The
dominant protocols of the Internet like TCP/IP, as well as the Point-to-Point Protocol (PPP),
which have become standard for establishment of links between Internet applications, are
combined with the PACTOR modes. The result of this intelligent protocol combination is a
data transparent and relatively fast Internet access via HF-radio using standardized user
interfaces. The
P4
dragon
appears to an attached PC as if it were a Hayes compatible "telephone
modem”. The
P4
dragon
locally takes over both the complete PPP and TCP/IP handling. Except
for a minimum fraction of protocol overhead, the physical PACTOR link only carries useful
data. The huge amount of overhead of the TCP/IP and PPP protocols (which are designed for
broad banded wired links) is reduced to the absolute minimum required. By locally carrying
out the PPP protocol between the PC and the
P4
dragon a further decisive advantage arises:
Because of the very short timeouts, PPP used to be nearly impossible over slow
communication channels with relatively large delays. Timeout problems are now solved by the
PACTOR-IP-Bridge.
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