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The digital operation mode PACTOR (Packet Teleprinting over Radio) has been specially developed for data transfer on shortwave. Thanks to PACTOR, faults that occur on these frequencies (fluctuations in signal strength, interference) can be compensated for. PACTOR uses synchronous transmission with error correction with 8 bit per character. For implementing PACTOR operation, special modems are required that switch between the terminal (usually a standard PC with corresponding program) and the transceiver. These modems with activated compression can achieve a data transmission rate of up to 5200 bps.
Modulation
In the case of the PACTOR III modem, a low-frequency, multi-carrier process with up to 18 individual carriers (tones) from 400 Hz to 2.4 kHz is used and each individual carrier is PSK-modulated. This means that PACTOR III has the bandwidth of an SSB sideband.
| Protocol level (SLV) | Number of tones (NTO) | Gross bit rate (PDR in Bit/s) | Net bit rate (NDR in Bit/s) | Crest faktor (CFR in DB) |
| 1 | 2 | 200 | 76.8 | 1.9 |
| 2 | 6 | 600 | 247.5 | 2.6 |
| 3 | 14 | 1400 | 588.8 | 3.1 |
| 4 | 14 | 2800 | 1186.1 | 3.8 |
| 5 | 16 | 3200 | 2039.5 | 5.2 |
| 6 | 18 | 3600 | 2722.1 | 5.7 |
PDR with compression
NDR without compression
Bit Rate
In order to increase the bit rate, a Huffman compression is used on the text level. Depending on the protocol level, the following bit rates can thus be achieved:
• Up to 3600 bps without compression
• Up to 5200 bps with compression