Timewave PK-900, Operating Manual

Page: 154 / 392

10.3 Using the SIAM Mode
After tuning in a signal as described above, make sure the THRESHOLD
is adjusted so the DCD LCD is lit. Then after about 10 seconds the
PK-900 should respond with a baud rate indication and confidence
factor similar to the one shown below.
0.47: 50 Baud,
After another 15 seconds or so, the PK-900 should respond with one
of the following signal classes and tell whether or not the signal is
reversed by giving the status of the command RXREV:
ASCII AMTOR ALIST Baudot Unknown noise 6-bit TDM
The complete information from the PK-900 signal analysis will look
something like the following:
0.47 50 Baud, Baudot, RXREV OFF
This means that the PK-900 has found the signal to be a 50-Baud
Baudot signal that is not inverted (since RXREV is OFF). The 0.47
means that the PK-900 is 47% sure that the baud rate is correct.
SIAM can identify and copy ASCII, ARQ and FEC AMTOR, Baudot and TDM
signals. To begin printing one of these signals, all that must be
done is to type the command OK after the analysis has been completed.
You should immediately begin to see text appear on your screen.
If the PK-900 determined the signal to be Unknown, 6-bit or noise
which it cannot decode, typing OK will cause the response:
?bad
The SIGNAL routine will run repeatedly until the operating mode is
changed either by typing OK, or forcing a change to another mode. If
you tune to a different signal during an analysis, simply type SIGNAL
again to restart the analysis routine.
10.3.1 Copying Encoded RTTY Transmissions
In the Short Wave bands many RTTY stations do not transmit in plain
text. Most of these stations are using sophisticated encryption
techniques that make receiving them almost impossible. There are a
few stations that use a relatively simple bit-inversion technique.
For these stations, the PK-900 has included the BITINV command.
If the text is not plain, but appears to be encoded, you can try
different settings of BITINV. BITINV will Exclusive-OR a number from
$00 to $1F with the received character of a Baudot signal thus
inverting specific bits. By varying BITINV from 0 through 31, you
will test all the different inversion possibilities that may encode a
Baudot signal. If only simple bit-inversion is being used, one of
the BITINV settings should cause the transmission to become readable.
If none of the 32 possibilities reveal plain text, then the
transmitting station is likely using a more sophisticated technique.
Computer programmers may be interested in the 5BIT and 6BIT commands.
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