DUP-ARQ is a semi-duplex system. The radio channel is used by a DUP-ARQ system in the same way as a simplex system, both stations alternating in transmitting blocks of five characters and a Hamming checksum. If a transmission error occurs a repeat request is initiated and the last data block is re-transmitted.
|
Parameter |
Value |
|
Frequency range |
HF |
|
Operation modes |
Semi-duplex ARQ |
|
Modulation |
FSK |
|
Symbol rate |
125 Bd, variable 30-650 Bd |
|
Receiver settings |
DATA, CW, LSB or USB |
|
Input format(s) |
AF, IF |
|
Additional Info |
ITA-2 with block coding |
DUP-ARQ operates at a Symbol rate of 125 Bd on the radio link.
If only one station is sending data, the other station transmits an IDLE pattern and initiates RQ cycles in case of transmission errors.
DUP-ARQ has automatic channel selection facilities. Before transmission starts, the best available short-wave transmission channel is selected and its quality is continuously checked for the duration of the transmission. Within a given frequency range the system may select one of 5 possible channels which are spaced at 400 Hz intervals. Because of this channel selection mechanism, the two linked stations may transmit at different frequencies.
The polarity of the bit stream (upper sideband (USB) or lower sideband (LSB)) cannot automatically be derived from the signal. Polarity may be manually selected by using the Polarity menu field. Polarity inversion does not cause a loss of signal synchronization.