With PACTOR-II-FEC, a modern, narrow-band and reliable two-channel PSK mode is available, which covers the needs of professional users for a secure and fast data transmission system. The good performance during disturbances and a small bandwidth of 500Hz are achieved by the use of a two channel DPSK modulation.

In contrast to PACTOR-II, modulation and block length in PACTOR-II-FEC is fixed to "DQPSK LONG BLOCK". Where PACTOR-II uses ARQ, i.e., after each block sent, an acknowledge message from the receiving station is required, PACTOR-II-FEC has no acknowledge return channel. Thus, the receiving station must be able to do all the error correction. This is achieved by using a Viterbi decoder with k = 9 and code rate = ½. Interleaving protects the transmission against fading. Using a DQPSK modulation is a good compromise when looking at the amount of bits transmitted and the necessary signal-to-noise-ratio.

To extract the data from a PACTOR-II-FEC signal, the signal is received and demodulated with a two channel DPSK-demodulator. The center frequency must be adjusted to the midpoint between the two channels. To achieve the best performance, the AFC (automatic frequency control) should be enabled. After the demodulation and the bit synchronization, the symbols of the two channels are combined to one bit stream. After the modulation type has been determined, the resulting bit stream is de-interleaved, passed through a Viterbi decoder and the CRC is checked.

PACTOR-II-FEC uses the same compression algorithms and CRC masks as PACTOR-II.

Options | CRC Recognition. The detected CRC is displayed in the decoder status bar, see CRC Recognition.

Using Options | CRC Table a certain CRC mask can be defined, see CRC Table.

Tuning a PACTOR-II-FEC signal

See PACTOR-II.