Hardware Reference¶
M5Stack Tab5¶
- Processor: ESP32-P4 @ 360 MHz
- RAM: 2 MB SRAM + 28 MB PSRAM
- Storage: 16 MB flash (firmware + settings)
- Display: 5" IPS LCD, 720×1280 landscape (10-bit parallel)
- Touch: ST7121 or ST7123 capacitive (100 kHz I2C)
- Audio: I2S codec ES8388 (CW audio output)
- WiFi: C6 co-processor (WiFi 6 802.11ax)
- USB: USB 2.0 host (USB-A port) + USB 2.0 device (USB-C port)
- Battery: 2500 mAh Li-poly (~4 hours panadapter, ~6 hours idle)
- RTC: Epson RX8130CE + 70 mF supercap (30–40 h time retention)
- Optional Keyboard: M5Stack SKU A164 (STM32F030, I2C slave @ 0x6D)
- Optional USB mouse (v1.3.0): plug into the USB-A port — a cursor appears and clicks drive every control. The mouse and the QMX cannot share the port: a USB hub doesn't help, because the ESP32-P4's USB host lacks the Transaction Translator a high-speed hub needs for full/low-speed devices. Use the mouse for setup, log review and manual reading with the radio unplugged.
QRP Labs QMX / QMX+¶
USB Audio (UAC)¶
- Interface: USB Audio Class (no drivers needed)
- Format: Stereo I/Q, 48 kHz sample rate, 24-bit PCM
- Latency: ~50 ms (ring buffer)
- I/Q Offset: +12 kHz IF (VFO signal at +12 kHz in baseband)
USB CAT (CDC-ACM)¶
- Interface: USB CDC-ACM (virtual serial port)
- Baudrate: 9600 (fixed)
- Protocol: Kenwood-style commands (FA, MD, FW, TX, RX, PC, SW, etc.)
- Format: Command; (terminated with semicolon)
CAT Commands (Reference)¶
| Command | Query | Set | Notes |
|---|---|---|---|
| FA | FA; -> FA14074000; |
FA14074000; |
Frequency (Hz) |
| MD | MD; -> MD2; |
MD2; |
Mode (1=LSB, 2=USB, 3=CW, 5=DiGi) |
| FW | FW; -> FW2500; |
FW2500; |
Filter width (Hz, SSB only) |
| TX | — | TX; |
Key transmitter |
| RX | — | RX; |
Release transmitter |
| TA | — | TA14074000; |
Tune and key (FT8 burst) |
| PC | PC; -> PC05.0; |
PC05.0; |
Power (watts, query only) |
| SW | SW; -> SW1.25; |
— | SWR (query while keyed) |
| TM | TM; -> TM123000; |
— | Time (hhmmss, query only) |
| VN | VN; -> VN1_03_002QMX; |
— | Firmware version (query only) |
SSB Filter Control (Special)¶
The QMX menu-manager controls SSB filter via:
MMSSB|Filter RX=<hz>;— commit filter (persists)MMSSB|Bandwidth=<hz>;— apply live filter- Both must be set to the same value for a clean change
See CLAUDE.md for the full recipe.
Cables¶
One cable does two jobs. The same USB lead carries the CAT commands out and the I/Q audio back — there is no second cable and no audio lead. The Tab5 is the host, so it is USB-A at the Tab5 end and USB-C at the radio, and a charge-only lead will look plugged in and do nothing.
Tab5 <- QMX (USB Audio + CAT)¶
- Type: USB-A (Tab5 host) -> USB-C (QMX)
- Data lines: Required (not charge-only)
- Power: Carries 5 V to QMX (optional; QMX can be separately powered)
- Cable quality: 3 m or less recommended (signal integrity)
Tab5 <- Power¶
- Type: USB-C, 5 V DC
- Current: 2 A minimum (Tab5 draws ~2.5 A at full brightness + FT8 TX)
- Source: USB power adapter, power bank, or solar panel
Frequency Ranges¶
Band coverage depends on which radio you have:
- QMX+ — full 160 m through 6 m coverage.
- QMX — ships in fixed band-group builds (for example 80/60/40/30/20 m, or 60/40/30/20/17/15 m, or 20/17/15/12/10 m). A given QMX only covers the bands it was built for, not the whole range below.
The panadapter works on whichever bands your radio supports:
| Band | Frequency | Notes |
|---|---|---|
| 160 m | 1.8–2.0 MHz | QMX+ only |
| 80 m | 3.5–3.8 MHz | — |
| 60 m | ~5.3–5.4 MHz | Channelised in many regions |
| 40 m | 7.0–7.3 MHz | — |
| 30 m | 10.1–10.15 MHz | SSB not available (CW/DiGi only) |
| 20 m | 14.0–14.35 MHz | Most FT8 activity |
| 17 m | 18.068–18.168 MHz | — |
| 15 m | 21.0–21.45 MHz | — |
| 12 m | 24.89–24.99 MHz | — |
| 10 m | 28.0–29.7 MHz | — |
| 6 m | 50–54 MHz | QMX+ only |
The Tab5 panadapter shows roughly a 48 kHz span (±24 kHz around the VFO) by default, narrowing as you zoom in. This is the full bandwidth of the QMX's 48 kHz IQ audio stream over USB.
Power Consumption¶
Tab5 (estimated)¶
| State | Current | Duration (2500 mAh) |
|---|---|---|
| Idle (display off) | ~50 mA | 50 h |
| Panadapter (RX only, display on) | ~600 mA | 4 h |
| FT8 RX (decoding, display on) | ~700 mA | 3.5 h |
| FT8 TX (5 W burst) | ~1.5 A | 1.5 h (peak) |
| WiFi + RX | ~800 mA | 3 h |
QMX / QMX+¶
| State | Current | Notes |
|---|---|---|
| Receive | ~80 mA | At 12 V |
| Transmit (5 W) | ~0.7 A @ 12 V ~1.0–1.1 A @ 9 V |
A lower supply voltage draws more current for the same RF output |
Running both devices in the field: a Tab5 (2500 mAh internal) plus a small external battery for the QMX gives roughly 2–3 hours of active FT8 operation — the Tab5's display and CPU dominate the total draw, not the radio.
RF Power Output¶
Both the QMX and QMX+ are 5 W-class transmitters delivering roughly 3–5 W, depending on band and supply voltage:
- Output is highest (~5 W) on the lower bands and tapers off toward the higher bands.
- The radio is built and tuned for either a 9 V or 12 V supply. Typical figures from QRP Labs: QMX ≈ 4–5 W at 9 V or 3–5 W at 12 V; QMX+ ≈ 3–5 W on either supply.
Both radios are the same 5 W power class — the QMX+ differs by covering more bands (full 160 m–6 m), not by transmitting more power.
Antennas¶
The QMX/QMX+ uses a 50 Ω coaxial antenna connector (SMA or BNC depending on model).
Recommended antennas: - Dipole (1/2 wave) — best all-round performance - EFHW (end-fed half-wave) — portable, single-wire - Vertical (1/4 wave + radials) — omnidirectional - Magnetic loop (small, tuned) — RFI rejection, low noise
Both are 5 W-class radios (≈3–5 W — see RF Power Output above) — a good antenna and low SWR matter at these QRP power levels.
Next: Review the Web API or troubleshoot via Troubleshooting.