Specifications

6.5.9 Operating at Commercial or VHF Wide RTTY Shifts
Most commercial stations found in the non amateur Short Wave bands
operate with a wide Frequency Shift keying of either 425 or 850 Hz
shift. To allow these stations to be received other modems are
available in the PK-900 and can be selected with the MODEM command.
The following modems are available for Baudot and ASCII operation:
Radio Port 1 Modems
MODEM 1 AFSK Modem, 170 Hz shift, M 2125 Hz, S 2295 Hz, 45 bps
MODEM 2 AFSK Modem, 170 Hz shift, M 2125 Hz, S 2295 Hz, 100 bps
MODEM 3 AFSK Modem, 200 Hz shift, M 2110 Hz, S 2310 Hz, 45 bps
MODEM 4 AFSK Modem, 200 Hz shift, M 2110 Hz, S 2310 Hz, 100 bps
MODEM 5 AFSK Modem, 425 Hz shift, M 2125 Hz, S 2550 Hz, 100 bps
MODEM 6 AFSK Modem, 850 Hz shift, M 2125 Hz, S 2975 Hz, 100 bps
MODEM 7 AFSK Modem, 850 Hz shift, M 2125 Hz, S 1275 Hz, 100 bps
MODEM 10 AFSK Modem, 200 Hz shift, M 2110 Hz, S 2310 Hz, 300 bps
If your license permits, you can also transmit to these stations when
the appropriate MODEM number and data rate is selected.
6.5.10 The CODE Command for International RTTY Compatibility
The CODE command allows the PK-900 to receive (and sometimes send)
other RTTY character sets. Part 97.69 of the FCC rules specifies that
the International Telegraph Alphabet Number 2 (ITA #2) must be used by
U.S. stations when operating RTTY. This corresponds to the CODE 0
command (default), but you may want to see the CODE command for more
information on the capabilities of your PK-900.
6.5.11 Copying Encoded RTTY Transmissions
In the Short Wave bands many RTTY stations can be found that are not
transmitting in plain text. Most of these stations are using
sophisticated encryption techniques that make receiving them almost
impossible. There are a few stations however that use a relatively
simple bit-inversion technique to make them hard to copy. For these
stations, the PK-900 has included the BITINV command to allow the
SWL to decode these simple forms of encoded RTTY stations.
6.6 ASCII RTTY Operation
ASCII RTTY operation is almost identical to Baudot operation but there
are a few differences you must know. Because the ASCII code uses
seven bits to define a character (instead of the five bits used in the
Baudot/Murray code), the probability of receiving errors is somewhat
higher. For these reasons, ASCII is not used widely on the HF amateur
bands. However, some commercial and military HF stations as well as
W1AW do use ASCII.
6.6.1 Starting ASCII Operation
First you must enter the ASCII mode of the PK-900.
If you are using an AEA PAKRATT program, follow the instructions in
the program manual to enter the ASCII mode.
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