MIL-188-141B Appendix C defines the third generation (3G) high frequency (HF) radio technology including advanced automatic link establishment (ALE), automatic link maintenance, and high performance data link protocols. This advanced technology improves on the performance of previous similar techniques (e.g., 2G-ALE). The specification is issued by the US Department of Defense (DoD) in the "Interface Standard Interoperability and Performance Standards for Medium and High Frequency Radio Systems" (1st March 1999).

This mode employs 5 constituent burst waveforms BW0 to BW4 for the various kinds of signaling required in the system, so as to meet their distinctive requirements as to payload, duration, time synchronization, and acquisition and demodulation performance in the presence of noise, fading, and multi-path. All of the burst waveforms use the basic 8-ary PSK serial tone modulation of an 1800 hertz (Hz) carrier at 2400 symbols per second (Baud). The same modulation is used in MIL-188-110A serial mode.

The burst waveforms have the following preamble and data structure.

The data in the different burst waveforms is used for different purposes:

Ø BW0 is used for 3G-ALE PDUs (Protocol Data Unit)

Ø BW1 for traffic management PDUs and HDL (High-rate Data Link Protocol) acknowledgement PDUs

Ø BW2 for HDL traffic data PDUs

Ø BW3 for LDL (Low-rate Data Link Protocol) traffic data PDUs

Ø BW4 for LDL acknowledgement PDUs

The MIL-188-141B decoder processes the waveforms BW0, BW1, and BW4 only to their final stage, i.e., displays the user data bits (after deinterleaving and FEC decoding). The configuration (number of data packet, FEC encoding and interleaver) of BW2 and BW3 is negotiated during the peer-to-peer communication, e.g., between two modems. These two waveforms can not be decoded to their final stage. For the waveform BW3, the decoder just demodulates and display the bits. The “Confidence” for BW3 is the average value of each demodulated symbol over the whole frame.

The decoder displays the payload data of BW0 and BW1 in BINARY, HEX, ASCII ASYNC, ASCII ASYNC (7 data bits, 0 stop bit) and ASCII SYNC formats selected from Options/Message Type.

In the HEX mode the payload data is displayed as it is, MSB first.

In the ASCII ASYNC mode the payload data is displayed as ASCII character, i.e., one start-bit (0), 8 data-bits (one ASCII character) and at least one stop-bit (1). The 8 data-bits are LSB first. The display is stopped when 300 NULL (all zero in 8 data-bits) characters are received or if the async data structure is violated more than 80 times.

In the ASCII ASYNC (7 data bits, 0 stop bit) the data is displayed in a similar way – one start bit (0), 7 data bits (LSB first) and no stop bit. Also the display terminates when more than 300 NULL characters occur or the async data structure is violated more than 80 times.

In the ASCII SYNC mode the payload data is segmented into 8-bit (LSB first) ASCII characters and displayed.

The waveform BW4 has only 2 bits payload data, they are displayed in HEX format (MSB first).

Tuning the decoder

The decoder processes the signal in both SSB settings: USB and LSB. This can be selected with Polarity in the menu: NOR means USB and INV means LSB signal.