PACTOR is a form of digimode transmission used by radio amateurs that combines the best features from Packet Radio and AMTOR to improve the transmission of data on particularly on the HF bands. It is found that the relatively large amounts of data sent in each packet transmission can be difficult to receive correctly when conditions are poor. On the other hand AMTOR is relatively slow when conditions are good, and much higher data rates could be achieved with little difficulty. PACTOR aims to overcome these problems by having a system which is more adaptive to the prevailing circumstances.
PACTOR operates at two different speeds according to the conditions. Under normal conditions the system operates at 100 baud, and swaps to 200 baud if a good link is established. In the slow speed each packet of data is 14 bytes long. This takes a total of 1.12 seconds to send, and leaving a gap for an acknowledgement of 320 mS this makes the whole sequence 1.44 seconds long. In the fast mode at 200 baud, each packet is 28 bytes long.
When a link is to be established the transmitting station sends data at 100 baud. This initial packet contains the callsign of the amateur radio station being called. This is repeated at 200 baud. If the receiving station only receives the data sent at 100 baud, one type of acknowledgement is sent and communication is established at this speed. If the data sent at 200 baud is received correctly then another acknowledgement is sent, and the contact proceeds at 200 baud. Once established the PACTOR contact then continues in the same way as a normal AMTOR contact.
Summary of PACTOR characteristics
Some of the highlight characteristics and parameters for PACTOR are summarised in the table below.
|Symbol rate||100 or 200 baud|
|Typing speed||66 wpm (300 wpm in PACTOR II)|
|Bandwidth||500 - 600 Hz|
|ITU description PACTOR||600HF1B|
|ITU description PACRTOR II||500HG1B|
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