A new firmware for the ATU-10 automatic antenna tuner (hardware design by N7DDC), written from scratch. Its aim is the best possible match and a calm, stable tuner – not the fastest tune.
Status: 1.1.0, tested on the device. See the timeline below.
- What it does
- Download
- Flashing
- First steps
- Operation
- Settings
- Questions
- Development status
- Feedback
- License
- Credits
- Finds the best match, not the first one. The tuner looks at the whole range of relay settings first and then refines the most promising ones. In the simulator it reaches the best possible SWR (within 0.05) in practically all cases that can be matched at all (99.9 %), with random wires, EFHWs, dipoles, doublets and more. How tuning works
- Differences to FW 1.6, the original firmware: settings, search and tuning results side by side. Both search algorithms were run in the simulator against the same antennas: NG reaches SWR 1.5 or better in practically every case where that is possible, FW 1.6 in about 61 %. A purely technical comparison, not meant to belittle FW 1.6 or N7DDC's work. Comparison with FW 1.6
- Remembers the last 12 good tunes. Back on a band you used before, the tuner tries the remembered settings first: a band change then takes about 2 to 3 seconds instead of 5 to 6.
- Bypass with a short press, and back to the tuned setting.
- Settings in three ways: in a menu on the tuner, with an editor in your browser, or directly in the hex file.
- Keeps its setting after switching off, a reset or a battery change.
- Hardly any current while switched off: about 15 µA (FW 1.6: 75 µA). Even after switching off at LOW BATT, the tuner survives a few weeks in a drawer without deep discharge. Thanks to DL8DTL (Jörg) for his detailed measurements!
- Can always be updated over USB, to any other firmware too.
Version 1.1.0: on the
latest release page,
the hex file ATU-10_NG_1_1_0.hex, or a zip with the hex file and the
license. What is new: see the changelog.
All earlier versions stay available on the releases page.
-
Connect the tuner to the computer with a USB cable.
-
A USB drive appears. Copy the
.hexfile onto it. -
Wait until the tuner restarts and shows the greeting, two pages of 2 seconds: "ATU-10 / HARDWARE BY N7DDC", then the version "NG 1.1.0 / FIRMWARE BY DL8UG".
Any other firmware hex file for the ATU-10 can be flashed the same way at any time – this firmware never blocks the way back.
- Connect the transceiver to the tuner's input and the antenna to its output.
- Set the transceiver to 2 to 5 W and send a steady carrier (CW key down, FM or AM).
- Press the tuner's button for about ¼ s (long press). The display shows TUNE and the best SWR found so far; after a few seconds the relays stop clicking and the SWR reached is shown.
- Stop sending. The tuner keeps the setting – also when switched off – and remembers it for the next time on this band.
| Press | Action |
|---|---|
| short press | bypass on / off (back to the tuned setting) |
| long press (¼ s) | tune – send a carrier of 1 to 15 W |
| very long press (2½ s) | switch off; to switch on, hold the button for about 1½ s |
| short or long press while the display is dark | display on (nothing else happens) |
| held while switching on, through the greeting | setup menu (see Settings) |
Tuning needs a steady carrier of 1 to 15 W (settings 4 and 5); 2 to 5 W give the most exact readings. While tuning, the display shows TUNE and the best SWR found so far, and the green LED is on. A first tune usually takes 4 to 7 seconds, a tune on a band used before about 2 to 3 seconds.
- Without a suitable carrier the tune waits. After 1 second two small lines next to TUNE say why: WAITING FOR RF (no carrier), POWER TOO LOW (below setting 4) or POWER TOO HIGH (above setting 5), and the power line shows the power. After 10 seconds the tuner gives up with NO POWER, TOO LOW or TOO HIGH, and everything stays as it was. A carrier that comes while waiting starts the tune after 0.2 seconds.
- If the carrier stops for about 5 seconds during the tune, the tuner shows NO POWER. If it had already found something better, it keeps that, otherwise everything stays as it was.
- Short carriers work too, e.g. the CW key pressed for a second at a time: pauses of up to about 5 seconds are simply waited out, and after a longer pause the next tune within a minute goes on with the interrupted search instead of starting again. If the antenna measures clearly different by then (other band, other antenna), or bypass was switched on meanwhile, a new search starts. Switching off ends the interrupted search.
- A short press during tuning stops it; the tuner keeps the best setting found so far (STOP).
- If the transmitter is too strong for the measurement (the detector is above its range, from about 14 to 22 W depending on the battery), the tune stops after a few dozen relay steps with OVERLOAD.
- If no setting is better than the direct connection and the SWR there is above 1.2, the tuner switches the relays off (NO MATCH). At or below 1.2 the antenna is simply left connected directly, without a message.
Auto tune: while you transmit, the tuner tunes again by itself when the SWR is above 1.2 and has changed by more than 0.3 since the last tune (settings 6 and 7). It does not do that in bypass, and not within 3 seconds after a tune, and not again after a tune that changed nothing (STOP, NO POWER, OVERLOAD) as long as the SWR stays the same. After NO POWER in the middle of a search, it goes on with the next carrier (SWR above 1.2).
| Shown | Meaning |
|---|---|
| PWR = 5.0 W | transmit power, with a short peak hold (setting 10) |
| SWR = 1.05 | SWR, measured while transmitting from 0.1 W on (the last value stays); -.-- until the first measurement |
| BYP | instead of SWR: bypass is on |
| battery symbol | battery charge, 3.0 V empty .. 4.2 V full; blinks below 3.4 V |
| TUNE | tuning in progress |
| WAITING FOR RF, POWER TOO LOW, POWER TOO HIGH | small, next to TUNE: the tune waits for a carrier between settings 4 and 5 |
| BYPASS / TUNED | after a short press: bypass on / back to the tuned setting |
| NO POWER | no carrier for tuning |
| TOO LOW, TOO HIGH | no tune: the power stayed below setting 4 / above setting 5 |
| NO MATCH | nothing better than the direct connection found (SWR above 1.2), the relays are off |
| STOP | tuning stopped by a button press |
| OVERLOAD | too much power for the measurement; a tune stops |
| RECHARGE | every 9 seconds in place of the SWR: battery below 3.2 V, please recharge; the tuner still tunes |
| LOW BATT | battery below 3.0 V for three readings in a row (6 seconds): the tuner switches off; also shown at a restart after a voltage drop |
| POWER OFF | the tuner switches off (button held, see Button) |
| WDT RST, STACK RST | the firmware restarted itself after a fault (please report it) |
Instead of the big power line the display can show the relays: setting 13 (DISPLAY in the setup menu) = RELAYS.
- L and C: one cell per relay, the smallest coil or capacitor on the left (L 0.1, 0.22, 0.45, 1, 2.2, 4.5, 10 µH; C 22, 47, 100, 220, 470, 1000, 2220 pF). A filled cell is a relay that is on.
- Next to the cells the sum of the coils and capacitors switched in. These are the nominal values, without stray capacitance, wiring and tolerances.
- Top right the power, below it the side the capacitors are on: TX (transmitter side) or ANT (antenna side). With L = 0 or C = 0 the side makes no difference.
- The lower line works as in the classic view (SWR, TUNE, all messages). The battery is the small symbol behind the SWR value.
- While tuning, the cells show the best setting found so far, together with the SWR so far.
Every 3 seconds a LED blinks briefly and shows the battery: green above 3.7 V, green and red (yellow) from 3.6 to 3.7 V, red below 3.6 V. While tuning the green LED is on.
| Battery | The tuner |
|---|---|
| 3.4 V and above | works normally |
| below 3.4 V | the battery symbol blinks |
| below 3.2 V | RECHARGE every 9 seconds; tuning still works |
| below 3.0 V | LOW BATT, then it switches off |
Each step needs three readings in a row (6 seconds), so a short dip while transmitting or switching the relays does not count; a step ends only when the battery is 0.05 V above its threshold again. When switching on or waking up, the step applies at once (the mildest of three readings): below 3.0 V the tuner shows LOW BATT at once and switches off again without pulsing the relays. While it runs, switching off still needs the three readings. At 3.8 V and below the relay pulse is 1 ms longer, as a weak battery drives the coils slower. If the voltage still drops below 2.7 V, the processor resets itself (brown-out) and shows LOW BATT when it starts again.
Thanks to DL8DTL (Jörg) for his measurements and advice on the battery thresholds!
Without activity (no transmitting, no button) the display goes dark after 5 minutes and the tuner switches off after 30 minutes (settings 1 and 2, 0 = never). Transmitting or a button press switches the display on again. The relays keep their setting while the tuner is off.
For a transceiver that controls the tuner through the start and key lines:
| Start line pulled low | Action |
|---|---|
| 20 to 90 ms | bypass on (also while the display is dark) |
| 200 ms or longer, key line free | tune; the tuner holds the key line low while tuning |
New: all settings can be changed on the tuner itself – in the setup menu, without a computer and without flashing. Changing them in the hex file still works, and a browser editor makes that easy.
All details: Settings – the menu step by step, the menu item HEX VALUES, the editor, and the hex file byte by byte with a worked checksum example.
| # | Setting | Default |
|---|---|---|
| 1 | Display off after (minutes, 0 = never) | 5 |
| 2 | Power off after (minutes, 0 = never) | 30 |
| 3 | Relay pulse (ms) | 10 |
| 4 | Minimum power for tuning (in 0.1 W) | 1.0 W |
| 5 | Maximum power for tuning (W) | 15 W |
| 6 | Auto tune when the SWR changed by more than (from 8.0 on: practically never) | 0.3 |
| 7 | Auto tune on / off | on |
| 8 | Detector calibration b (1 W) | 4 (b = 0.4) |
| 9 | Detector calibration a (10 W) | 14 (a = 1.14) |
| 10 | Power peak hold | 600 ms |
| 11 | Tune target: stop at this SWR (0 = always the full search) | 1.05 |
| 12 | Search effort: 1 quick, 2 normal, 3 thorough | 2 |
| 13 | Display: classic, or the relay view | classic |
1. Menu on the tuner: keep the button pressed when switching on, through the greeting, until SETUP appears. A short press changes the value, a long press goes to the next setting. After setting 13 come three pages, each done with a short press:
- SAVE – keep the values and leave the menu
- HEX VALUES – delete the values saved in the menu; the settings written in the hex file (for a published file: the defaults above) apply again. The tuned relay setting and the memory of tunes stay. Use it to get back to a known state after trying things in the menu.
- EXIT – leave without saving
Without a press for a minute the menu ends without saving.
2. Editor in the browser: download tools/cell-editor.html,
open it (it works offline), load the hex file, change the values, save, then
flash the file.
3. In the hex file: the settings are 13 BCD coded bytes ("Cells") at
address 0xEEE0, in the lines starting with :10EEE000 (settings 1–8) and
:10EEF000 (9–13). Each setting is a pair of bytes: the value, written with
its decimal digits, and 34. Example: 10 34 = 10 ms relay pulse. After
changing a line its checksum (last byte) must be corrected – see
Settings; the editor does that
for you.
Which values apply: values saved in the menu take precedence over the hex file – until you flash a hex file with other settings (then those apply) or choose HEX VALUES in the menu.
The tuner does not find a good match. Check the power (1 to 15 W) and that the carrier is steady. Some antennas cannot be matched on some bands (the display then shows the best that was possible). Search effort 3 (setting 12) tries harder.
Tuning takes long. A first tune usually takes 4 to 7 seconds (rarely up to 15), a tune on a band used before about 2 to 3 seconds. Search effort 1 (setting 12) is quicker but finds the best match less often.
The tuner tunes again and again. Auto tune reacts to a changing SWR. If that is not wanted (e.g. with SSB on a critical antenna), switch it off (setting 7) or raise the threshold (setting 6).
Which settings are in effect? See Settings: which values are in effect. Choosing HEX VALUES in the setup menu brings back the values of the hex file.
The display stays dark. Press the button once. If the display still does not come on, switch the tuner off and on again.
| Date | Version | Status | Content |
|---|---|---|---|
| 2026-10-02 | 0.1.0 | development | complete new firmware: search, memory of 12 tunes, setup menu, Cells editor; simulator and PC tests |
| 2026-10-02 | 0.9.0 | release, tested on the device | first device tests passed; review fixes, display clean-up after tuning |
| 2026-10-02 | 0.9.1 | release, tested on the device | review fixes (auto tune near the minimum power, NO MATCH, tune target 0, bypass pulse during a tune), greeting on two pages, POWER OFF screen |
| 2026-10-02 | 0.9.2 | release, tested on the device | tuning with short carriers (CW key), no auto tune again after STOP, OVERLOAD stops a tune, memory order over many tunes, less current when switched off, display fixes |
| 2026-10-03 | 0.9.3 | release, tested on the device | review fixes for short carriers: new search after a change of band or bypass, switching off ends an interrupted search, no endless tunes on carriers too short to measure |
| 2026-10-03 | 0.9.4 | release, tested on the device | TUNE says why it waits (no RF, power too low or too high), SWR shown from 0.1 W, LOW BATT only after three low readings; review fixes; tests on GitHub on every push |
| 2026-10-04 | 0.9.5 | release, tested on the device | battery warnings in steps (symbol blinks below 3.4 V, RECHARGE below 3.2 V, off below 3.0 V), LOW BATT at once when switched on with an empty battery, relay pulse 10 ms as the data sheets ask, Cell editor shows the firmware version; review fixes |
| 2026-10-06 | 0.9.6 | release, tested on the device | less current while switched off, 15 µA (FW 1.6: 75 µA): display lines released, no input buffers on open lines |
| 2026-10-06 | 1.0.0 | release, tested on the device | nothing left to improve: the same as 0.9.6, only the version number grew up |
| 2026-10-10 | 1.1.0 | release, tested on the device | relay view (setting 13): the L and C relays, their values and the capacitor side on the display; capacitor side checked on the device |
More: Changelog · Settings in detail · How tuning works · Comparison with FW 1.6 · Development
Problems, questions and reports from use on the air are very welcome. Please report them with a detailed description
- as an issue here on GitHub (a form asks for the points below), or
- in the groups.io thread ATU-10 NG firmware.
Please include: the firmware version (shown in the greeting), the antenna and feed line, band and frequency, transceiver and power, what the display showed (SWR, messages), what you expected instead, and how to make it happen again.
Beerware (SPDX: Beerware): do whatever you want with it, as
long as you keep the license notice. If we meet some day, and you think this
stuff is worth it, you can buy me a beer in return.
Note
To the manufacturers of ATU-10 tuners
If you build and sell ATU-10 tuners: you are very welcome to use this firmware – that is what it is for. It is free and meant to serve the whole amateur radio community.
If it helps your product, I would be glad if you gave a little back to that community. Please get in touch: I would love to receive a small number of ATU-10 tuners for a youth project of our local or regional amateur radio club, so that young people can build antennas, tune them and get on the air.
Contact: DL8UG – open a GitHub issue, or find my contact details on QRZ.com.
致 ATU-10 天调的生产厂家： 如果您生产和销售 ATU-10 天调，欢迎使用本固件——这正是它的用途。它是免费的，旨在服务整个业余无线电爱好者群体。如果它对您的产品有所帮助，我很希望您能为这个群体回馈一点：请与我联系。我希望获得少量 ATU-10 天调，捐赠给我们本地或地区业余无线电协会的青少年项目，让年轻人亲手架设天线、调谐天线，并开始上机通联。联系方式：DL8UG——请在 GitHub 上提交 issue，或通过 QRZ.com 查找我的联系方式。
The ATU-10 hardware is a design by David Fainitski, N7DDC. The pin assignment, the relay pulse sequence, the display initialization and the 5x8 font follow his ATU-10 firmware, which he released into the public domain. Everything else in this firmware is written anew by DL8UG.
Developed with the help of Claude Code.