Which tuner for HL2 + IO board + planned Neptune 100W (remote setup)? Is an ATU-100 sufficient?

[Martin S.]

Hi everyone,

I'm expanding my Hermes Lite 2 setup. I already have the HL2 IO board installed and plan to add a Neptune/APM 100W amplifier soon. For budget reasons, I'm considering an ATU-100 (N7DDC type).
Before buying, I’d like to clarify a few key points for reliable remote operation.

My setup and requirements:

• HL2 with IO board

• Planned PA: Neptune/APM 100W

• Remote operation (tuner and switching must work remotely)

• Budget-friendly → ATU-100 preferred (kit or assembled)

My main questions:

1. Is the HL2 IO board required to trigger tuning only when Thetis sends a TUNE command?

2. Can I simply connect the ATU-100’s TUNE button pads to a low-side output on the IO board, or is additional firmware/interlock logic needed?

3. Does the ATU-100 auto-tune on power-up / HF input, or only when externally triggered?

4. Which ATU-100 firmware/version reliably starts in AUTO mode and remembers the mode after reboot?

5. Which ATU-100 hardware version is best for remote + 100W?

   • Mini (5×5) vs Extended (7×7)?

   • Kit vs assembled? (e.g., easier access to TUNE pads vs overall build quality)

6. Recommended wiring: HL2 IO → ATU-100 TUNE pad, PTT interlock for PA, shared ground, etc. Any pin/pad recommendations from your experience?

7. ATU placement: HL2 → PA → ATU or HL2 → ATU → PA — what works best/safest with the Neptune + ATU-100 in a remote setup?

8. Any practical issues to be aware of? (e.g., preventing PA from keying during tuning, tune-power settings in Thetis, avoiding unwanted auto-tuning)

Thanks in advance — especially interested in experiences from anyone running HL2 IO + ATU-100 remotely with a PA.

73,
Martin, DB3MAR