2G ALE (MIL-STD-188-141B appendix A)

hfmodem.bateleur.ale receives and generates 2G ALE words for monitoring and operator-directed calls and links. The operator can enable scanning to retune the rig through a configured channel list. Host commands and events are in ALE-HOST.md.

Interoperability evidence

The transmitter sends each tone's three bits most significant first. Local round trips test that choice; the unrecorded LinuxALE result does not provide a retained interoperability fixture. The capabilities report follows figure A-45's four DATA words after CMD, rather than the five named in A.5.6.6.2.2. A captured capabilities reply with decoded fields would settle that discrepancy.

Earlier performance tables quoted 100 handshakes per point and link times of 13.0–13.3 seconds. Their harness and raw results were not retained. The executable tests under tests/bateleur/ale exercise selected simulated channels; they do not reproduce those tables.

DTM and DBM

DTM uses 21-bit data fields with alternating DATA/REP preambles. This implementation checks the message and stuffing bits in those fields, excluding the CMD DTM and each three-bit preamble. It uses polynomial 0x1021, preset 0xFFFF, final complement, most significant bit first. ASCII stuffing is DEL; binary stuffing is ones. A bare CMD CRC elsewhere covers whole 24-bit words.

This reading is unverified against a foreign implementation. In the public MIL-STD-188-141B text, figure A-48 (printed page 175) labels the reconstructed example CRC 0x2C5B. For THE QUICK BROWN FOX! plus seven DEL stuffing bits, this code computes 0xDB2A; with seven zero stuffing bits it computes 0x5452. Neither matches. The figure is unresolved evidence, not an illustrative value to discard. A foreign DTM recording must retain the complete CMD DTM, every DATA/REP word including stuffing, CMD CRC and the ACK/NAK exchange, with the original message bytes and receiver output. A repeated damaged block would also settle combining behavior.

DTM NULL replies currently use KD4=1 for affirmative participation; DTM ARQ uses KD4 as ACK/NAK rather than data type. These readings also need that foreign exchange. Messages end in a BASIC block; received partial messages are also delivered on a new message sequence, NULL, or link end.

DBM encodes 12-bit groups as Golay rows, interleaves by column, and places the CRC in the final 16 bits of the padded data field. A foreign BASIC and EXTENDED exchange with known bytes, depth, stuffing and ACK/NAK would settle its wire format. Protected DBM additionally needs both endpoints' test key, UTC and channel frequency to verify pair numbering.

Outbound DTM/DBM queues hold at most 16 messages and 65,536 bytes. Blocks are sized to [rig] max_key_s, including the full source and destination addresses. If the smallest block does not fit, the command reports an error. A complete call, response, sound or AMD frame that exceeds the limit is refused with its duration; it is never cut into incomplete ALE frames. The configured channel count, address lengths and sounding duration must therefore fit the selected limit. Retries stop after seven attempts; a block exchange, including requested pauses, is capped at five minutes.

Reception retains DTM/DBM recognition and combining. The receiver bounds announced blocks by its configured DTM word and DBM depth limits and drops an unfinished block after its expected receive window. Nonfinite samples are replaced with zero. A steady single tone does not extend ALE activity indefinitely, and a signal-detection episode has a finite scan hold.

Linking protection

AL-1 and AL-2 encrypt ALE words under a shared 56-bit key before Golay coding. [protocols.ale] lp_level is zero by default; 1 selects AL-1 and 2 selects AL-2. lp_key is fourteen hexadecimal digits. Startup reports the selected level without printing the key.

The operator's chosen part97 station profile excludes linking protection, regardless of channel. Under unregulated, startup and each transmit attempt warn when the dial lies in an amateur band-plan range. The check uses the same HF ranges as the logbook, including its broad 5.30–5.41 MHz 60 m range. These are configured profile limits.

The implementation uses date, time, word number and frequency in the seed. AL-1 uses 60-second protection intervals; AL-2 uses two seconds. The receiver searches the current and adjacent intervals and retains protected traffic recognition. Its candidate ranking and one-word lookahead are local receive choices. Single-word protected detections are discarded because they are too ambiguous under the candidate seeds.

TIME and TIMECAST exercise protected and clear time acquisition. A foreign recording spanning an interval boundary, with known key, UTC, frequency, clear authentication word and DBM payload, is needed to check the numbering and time exchange. AL-3, AL-4, passive time acquisition and the second-transmission restriction within one AL-2 interval are not implemented.

On a station

[protocols.ale]
enabled    = true
host       = "ale"
port       = 8330
addresses  = ["N0CALL"]
channels   = [7102000, 10145500, 14109000]   # dial frequencies in Hz
scan_rate  = 2.0
activity_s = 30.0
sound_s    = 1800.0
nets       = [{address = "NET1", member = "N0CALL", slot = 2}]

Host connections use the normal host opening. sound_s is zero to disable periodic sounding, or at least 60 seconds. activity_s must be finite and nonnegative. With conventions = "hflink", the HFLINK preset supplies the activity and sounding intervals; explicit activity_s and sound_s entries must be removed. base and pilot_channels require that preset. The operator supplies the channel list.

ALE holds scanning while another lane reports an active link, checks that a requested tune succeeded, and checks the dial again before sending on a channel. On stopping, it restores the configured station centre. Tune failures name the dial frequency and the rig error. This coordination is within this station process. The shared rig claim excludes cooperating processes from simultaneous hardware ownership; it does not coordinate their channel plans or share ALE link state. See station ownership.

Other lanes' transmissions update ALE link activity. The arbiter reserves an active lane's link against unrelated transmit errands. Individual responses are limited to one per caller per minute, with at most 64 recent callers. Repeated AllCalls do not refresh an established link's activity.

The receiver currently ends an ALE frame after an empty redundant-word slot. The response budget is 5 Tw, about 653 ms; the empty slot consumes 392 ms. Software timing tests exclude hardware PTT, device buffering and rig settling. A synchronized recording of the incoming final tone, PTT and outgoing first tone is required to verify turnaround on a station. No physical turnaround measurement is established here.

Net response slots whose earlier members are unknown assume one-word addresses. A net with longer earlier addresses needs an explicitly agreed slot plan. Group scanning calls alternate THRU/REP and leading calls use TO/REP; these choices need a foreign group-call recording with known member order and addresses.

Monitoring directory

ale.directory reads the community ALE user list and local CSV files of kind,key,agency,description. Configure directory = ["default", "ours.csv"] to load them in the background; WHO and first-heard events show matches. hfmodem ale-list lists entries, and its fetch, who, freq, agency, channels and acronym subcommands query or refresh them. Sources are identified on entries. A malformed refresh retains the last parseable cache; a successful refresh replaces it atomically.

Directory, DTM/DBM and protected-traffic monitoring remain available. Channel lists are not restricted to transmit profile segments at load; each transmission still passes through the station's emission checks.