Timewave PK-900, Operating Manual, Page: 269 / 392

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SAmple "n" Immediate Command
Mode: Command Host: SA
_________________________________ Parameters: __________________________________
"n" - 20 to 255 specifies the sampling rate in baud.
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This operating mode is for advanced users interested in decoding unknown
synchronous data transmissions. SAMPLE is similar to the 5BIT and 6BIT modes,
but operates on synchronous data, whereas 5BIT and 6BIT are used on signals
known to be asynchronous.
SAMPLE synchronizes up on any regularly-paced data transmission received on
Radio
Port 1 and samples the data once per bit, packaging the data in groups and
sending the groups to the user for further analysis. The user can use SAMPLE to
capture data bits from a synchronous transmission, such as FEC, TDM or an
"unknown mode" not identified by the SIGNAL command. The transmission is
actually sampled several times per data bit. The PK-900 does a majority vote
on the last few samples to represent the value of the data bit.
One use for the SAMPLE command is to record the output to a disk file, then
write a program to analyze the results for synchronous/asynchronous, bit sync
patterns, data decoding, etc.
SAMPLE data is captured in 6-bit units; the order of bit reception is MSB first,
LSB last. The TNC sends the data unit to the user with a constant of hex 30
added to each unit, the same as the 6BIT command. The 6-bit unit is a
compromise between hexadecimal and 8-bit binary output. The 6-bit unit yields
shorter disk files than 4-bit hexadecimal characters, but encounters no
interference from terminal communications programs and the TNC's Converse and
Command modes. The 6-bit unit's range of $30-6F falls within the printable
ASCII range, allowing the TNC to insert end-of-line carriage returns that can be
ignored by the user's analysis software.
To use SAMPLE, set ACRDISP to a non-zero value such as 77. This will break up
the recorded disk file into lines. Tune in the signal, set WIDESHFT ON or OFF
as needed, and get the transmission rate from the SIGNAL command. Now type
"SAMPLE (rate)". As an example, SIGNAL may identify a transmission as 96 baud
TDM; in this case type the following:
SAMPLE 96 <Carriage Return>
Now begin the capture to a disk file with the terminal program. At the end of
the session, edit the disk file and remove any TNC commands that were echoed
before or after the received data.
Occasionally SIGNAL will identify a Baudot transmission at a rate that SAMPLE
cannot sync up on. This would happen if the Baudot signal had a stop bit
duration 1.5 times the data bit duration. In this case, SAMPLE at twice the
baud rate and compensate for the doubled data bits in the analysis software.
Note that it might be more useful to let the TNC do the start/stop bit work by
using the 5BIT command rather than SAMPLE. 5BIT uses RBAUD, and adds a constant
of hex 40 to each 5-bit character received.
Note: RXREV does affect the sense of the SAMPLE data.
RXREV should however not be changed while capturing data.
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