Link-11 (CLEW: Conventional Link Eleven Waveform), also known as TADIL-A, is a transmission mode mostly in HF band, to run a tactical digital information network. This mode is specified by the US Department of Defense (DoD) in MIL-STD-188-203-1A (8th January 1988).
|
Parameter |
Value |
|
Frequency range |
HF |
|
Operation modes |
Multi-carrier, DQPSK |
|
Symbol rate |
75 Bd or 45.45 Bd |
|
Modulation |
16-tone, DQPSK |
|
Receiver settings |
USB |
|
Shift/Bandwidth |
2310 Hz |
|
Center |
1650 Hz |
|
Receiver settings |
DATA, CW, LSB or USB |
|
Input format(s) |
AF, IF |
This mode has 16 carriers: one Doppler tone at 605 Hz; 14 data carriers starting at 935 Hz with tone distance of 110 Hz and the 16th carrier at 2915 Hz is used for data and synchronization, see table below. Except the Doppler tone, other carriers are DQPSK, modulated at the symbol rate of 75 or 45.45 Baud.
|
Number |
Frequency (Hz) |
Description |
Bit location |
|
1 |
605 |
Doppler |
- |
|
2 |
935 |
Data |
0 and 1 |
|
3 |
1045 |
Data |
2 and 3 |
|
4 |
1155 |
Data |
4 and 5 |
|
5 |
1265 |
Data |
6 and 7 |
|
6 |
1375 |
Data |
8 and 9 |
|
7 |
1485 |
Data |
10 and 11 |
|
8 |
1595 |
Data |
12 and 13 |
|
9 |
1705 |
Data |
14 and 15 |
|
10 |
1815 |
Data |
16 and 17 |
|
11 |
1925 |
Data |
18 and 19 |
|
12 |
2035 |
Data |
20 and 21 |
|
13 |
2145 |
Data |
22 and 23 |
|
14 |
2255 |
Data |
24 and 25 |
|
15 |
2365 |
Data |
26 and 27 |
|
16 |
2915 |
Data / Sync |
28 and 29 |
There are 5 frame formats:
•DNCS IM: Data Net Control Station Interrogation Message
•DNCS IWM: Interrogation with Message
•PRM: Picket Reply Message
•SB: Short Broadcast
•Net Test
The data in the frames is coded with Hamming method.
To decode the mode, choose the correct Polarity, put the Doppler Tone cursor in the FFT tuning window to the Doppler tone. Small frequency error (+/- 30 Hz) and Doppler shift will be corrected automatically and displayed in the Freq Err/Doppler Shift field. The data will be displayed in the main text window. Because the mode transmits link information, the data is displayed in a 30-bit group hex.
The frame format is displayed together with the baudrate in the Format field. Confidence shows the decoding quality: a value over 95 means the FEC has probably corrected all bit errors, the data decoded is mostly reliable.