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After another 15 seconds or so, the <strong>PK</strong>-<strong>232</strong> should respond with one of<br />
the following signal classes and tell whether or not the signal is<br />
reversed by giving the status of the command RXREV:<br />
ASCII AMTOR ALIST Baudot Unknown noise 6-bit TDM<br />
The complete information from the <strong>PK</strong>-<strong>232</strong> signal analysis will look<br />
something like the following:<br />
0.47 50 Baud, Baudot, RXREV OFF<br />
This means that the <strong>PK</strong>-<strong>232</strong> has determined the signal to be a 50-Baud<br />
Baudot signal that is not inverted (since RXREV is OFF). The 0.47<br />
means that the <strong>PK</strong>-<strong>232</strong> is only 47% sure that this analysis is correct.<br />
SIAM can identify and copy ASCII, ARQ and FEC AMTOR, Baudot and TDM<br />
signals. To begin printing one of these signals, all that must be<br />
done is to type the command OK after the analysis has been completed.<br />
You should immediately begin to see text appear on your screen.<br />
If the <strong>PK</strong>-<strong>232</strong> determined the signal to be Unknown, 6-bit or noise<br />
which it cannot decode, typing OK will cause the response:<br />
?bad<br />
The SIGNAL routine will run repeatedly until the operating mode is<br />
changed either by typing OK, or forcing a change to another mode. If<br />
you tune to a different signal during an analysis, simply type SIGNAL<br />
again to restart the analysis routine.<br />
10.3.1 Copying Encoded RTTY Transmissions<br />
In the Short Wave bands many RTTY stations can be found that are not<br />
transmitting in plain text. Most of these stations are using<br />
sophisticated encryption techniques that make receiving them almost<br />
impossible. There are a few stations however that use a relatively<br />
simple bit-inversion technique to make them hard to copy. For these<br />
stations, the <strong>PK</strong>-<strong>232</strong> has included the BITINV command.<br />
If the text is not plain, but appears to be encoded, you can try<br />
different settings of the BITINV command. BITINV will Exclusive-OR a<br />
number from $00 to $1F with the received character of a Baudot signal<br />
thus inverting specific bits. By varying BITINV f rom 0 through 31,<br />
you will test all the different bit-inversion possibilities that may<br />
be used to encode a Baudot signal. If only simple bit-inversion is<br />
being used, one of the settings of BITINV should cause the<br />
transmission to print in plain text. If however, none of the 32<br />
possibilities reveal plain text, then the transmitting station is<br />
likely using a more sophisticated encryption technique. Computer<br />
programmers may be interested in the 5BIT and 6BIT commands.<br />
10.3.2 The CODE command for International RTTY Compatibility<br />
The CODE command allows the <strong>PK</strong>-<strong>232</strong> to receive (and sometimes send)<br />
other RTTY character sets. Look up the CODE command in the Command<br />
Summary Appendix for information on some of the other character sets<br />
you may encounter on the HF bands.<br />
4/91 10-3<br />
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