Timewave DSP-232, Operating Manual

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Chapter 12 PACTOR Operation
Chapter 12
PACTOR Operation
Overview
PACTOR is a relatively new amateur data communications mode; it was developed in Germany by Hans-Peter
Helfert, DL6MAA, and Ulrich Strate, DF4KV. PACTOR combines some of the best features of both AMTOR and
Packet as well as providing a few new features which we’ll cover later in this chapter. PACTOR operates at 100 bps
or 200 bps, depending on atmospheric conditions and the quality of the received signal. PACTOR also provides
near error-free throughput and can also selectively use a data compression scheme (Huffman encoding) to increase
throughput when transmitting text. Since PACTOR uses 8-bit words, you can use the full ASCII character set.
Another advantage of PACTOR is when data blocks are repeated in the case of an error in reception, the DSP can
often combine the bad blocks of data into a good ones without the need of receiving a perfect block in the first
place. This scheme is called “memory ARQ”(Automatic ReQuest for reception). Like AMTOR and Packet,
PACTOR has two basic modes of operation: an ARQ (linked) mode and a non-linked mode used for CQ calls and
roundtable operation.
When listening to an ARQ PACTOR conversation, you’ll hear a 960 mS burst of data from the sending station
followed by a short burst from the receiving station—back to the transmitting station—to acknowledge (ack) or
non-acknowledge (nack) reception of the sent data. The nack signal is sent by the receiving station when the error-
checking scheme (CRC) detects an error in the received data block. Like packet, PACTOR is mark-space polarity
independent—the PACTOR protocol purposely alternates the data polarity with every transmission as a means of
reducing the effects of interference.
In PACTOR, the transmitting station (ISS) “has the link” and requires a periodic “ack” signal from the receiving
(IRS) station as part of its error-checking scheme. An analogy of this would be you reading off sequences of
numbers to a friend and having him acknowledge them back, then when you’re finished you’d switch roles with him
and he’d call off his set of numbers.
When you’re reading off your set of numbers (transmitting) you have control of the link since you’re the sending
station. Your friend, the “receiver,” answers back (acknowledges) with either a quick “yes, I heard you okay” or a
“no, I missed something.” In the former case, you’ll “send” the next sequence of numbers; in the latter, you’ll repeat
the previous number sequence. After you’ve read all the numbers on your list, you’d hand the link over to your
friend and it’d be his turn to read numbers to you and for you to acknowledge them as “received okay” or “not
received okay.”
The unproto(col) mode of PACTOR operation is a non-linked type of operation. It’s used for roundtable operation
or for calling CQ. The unproto mode repeats the data blocks “
n ” times and can use either 100 or 200 bps. (It also
uses the CRC error-check scheme.)
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