87 lines
4.0 KiB
Markdown
87 lines
4.0 KiB
Markdown
# ACOM built-in ATU — what we know, and why OpsLog does not drive it
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Session of 2026-08-02 on F4BPO's friend's **ACOM 500S**, serial link, telemetry
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trace. Written down so nobody repeats the work. **Conclusion first: the tuner
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cannot be started over the serial link, and the attempt to work around that was
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abandoned.**
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## The tuner is PA state 8
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Frame byte 3's high nibble is the PA status. ACOM's own list (recovered by the
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ACOM-Controller project) has no entry for 8; it is the antenna tuner. Confirmed
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twice, front-panel TUNE, with the byte-level trace running:
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```
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14:47:20.745 state 8 step 0 ← TUNE pressed. err=FF
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14:47:22.588 operator keys a carrier (FT-891, FM, 31 W, 3.6358 MHz)
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14:47:24.006 state 8 step 2
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14:47:25.201 state 8 step 4
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14:47:27.457 state 8 step 5
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14:47:30.092 state 5 STANDBY ← accord finished
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```
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Byte 3's **low** nibble is a step counter through the accord: `0 → 2 → 4 → 5`.
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Step 0 means *armed, waiting for RF* — in the first of the two runs the
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amplifier sat there **30 seconds** untouched before the operator transmitted.
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`paStatusNames[8] = "TUNE"` in acom.go is the only thing kept from all of this.
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## The command does not exist in the state-command family
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Every action byte of `55 81 08 02 00 XX 00 CHK` was tried, each one from a
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**verified** STANDBY (an earlier sweep was worthless because its second code
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parked the amp in SERVICE, where it silently refuses everything — 17 false
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negatives). Result:
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| byte | effect |
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|------|--------|
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| 0x01, 0x02 | **reboot the amplifier** — it prints `AMPLIFIER: ACOM 500S / HELLO ME…` |
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| 0x04 | → SERVICE (state 4) |
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| 0x05 | → STANDBY (state 5) |
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| 0x06 | → OPERATE (state 6) |
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| 0x0A | → OFF (state 10) |
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| 0x03, 0x07..0x09, 0x0B..0x18 | nothing, state unchanged |
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The action byte **is** the target PA state — four independent confirmations.
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Which makes 0x08 the obvious candidate for TUNE. **It was tried, from a verified
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STANDBY, and does nothing.** State 8 is reachable from the front panel only.
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Going further would mean varying the other bytes of the frame. That is a large
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space, and 0x01/0x02 prove that bad values reboot a 500 W amplifier. Not worth
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it.
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## The workaround that was built and removed
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Since the amp waits, armed, for a carrier, OpsLog could watch for state 8 and
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supply one: memorise the mode, drop the power, switch to FM, key the PTT, wait
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for state 8 to clear, unkey, restore. It was implemented (`acomtune.go`, opt-in,
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Settings → Amplifier) and **removed** after the first hardware test:
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- the power change did not take effect, and
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- **the PTT was not released when the tune finished.**
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A logger that can leave a transceiver keyed is not acceptable, and the whole
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thing was scaffolding around a protocol we do not actually control. Removed at
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the operator's request: *"je veux qu'OpsLog soit solide et ça c'est de la
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bidouille."*
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If it is ever revisited, the unexplained part is why the tune-finished detection
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did not fire — `anyAcomTuning()` polled `StateRaw == 8` every 200 ms and should
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have seen the drop to STANDBY. Suspect the status snapshot, not the amplifier.
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## Loose ends worth knowing
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- **Frame byte 6 is a multiplexer.** The tail of the frame changes meaning with
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it: `0x93` = bytes 48/49 carry the TX frequency in kHz (`62 1B` = 7010 while
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the rig was on 7.010 MHz), `0x9D` = something else. Byte 70 looked like a
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tuner flag for a while purely because of this — it toggles on its own several
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times a minute. Do not read tail bytes without checking byte 6.
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- **Byte 5 bit 0x80 alternates frame to frame.** It is a sequence/parity bit,
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not a command acknowledgement.
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- **Byte 66 (the error code) shows 0x14 / 0x8E / 0x69 / 0x0F during a normal
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tune and during transmission.** `errText` renders those as "ERROR — see
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display" and "Remove drive power", so an ACOM operator probably sees a false
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alarm. This was never confirmed with the amplifier in OPERATE (it was in
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STANDBY throughout, where drive genuinely is an error) — worth a look with a
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clean log before touching the table.
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