Radios

Xiegu XPA125B · Volume 3

Xiegu XPA125B — Vol 3: Programming

100W HF/6m amp with built-in antenna tuner

3.1 Programming workflow

The XPA125B has no codeplug in the traditional sense — no software, no USB-loaded channel database, no “CPS” tool. Configuration is split between front-panel menus (the runtime configuration that you’ll change between operating sessions) and DIP switches on the internal main board (the install-time configuration that you set once and forget).

3.1.1 Front-panel menu items

Enter the menu via the FUNCTION button. The exact menu structure varies by firmware version; the canonical items are:

  • ALC threshold: 0-100% (or equivalent voltage scale). Sets how aggressively the ALC output line clamps drive power. Start at ~80% and adjust empirically — too low and the amp can’t hit full output; too high and you risk over-driving and splatter.
  • Fan mode: auto / always-on / always-off. Auto is the default and the right answer for nearly every use case. Always-on is useful for hot-shack contesting where you want maximum cooling from the start. Always-off is a footgun — don’t.
  • Band detect mode: auto-sense / CAT-driven / manual. Auto-sense reads the input frequency and picks the band filter. CAT-driven reads the X6100’s CAT data. Manual locks to the band you select on the front panel. For an X6100-paired station with CAT connected, use CAT-driven; for a portable setup with no CAT, use auto-sense.
  • RF-sense sensitivity: 0-100%. How much input RF triggers the TX changeover. Too low and the amp keys on stray pickup; too high and it misses real drive. Default ~50% is typical.
  • VOX hold time: 50-500 ms. How long the amp stays in TX after RF drops. Tune for the mode — short for digital, longer for CW.
  • Display brightness: 0-100%.
  • Standby/operate: same as the front-panel switch but exposed in the menu for completeness.
  • Reset to factory defaults: a one-button factory reset. Useful when you’ve fiddled too much and want to start over.

3.1.2 Internal DIP switches

A small DIP block on the main PCB (visible after removing the top cover) controls install-time options:

  • Default ALC polarity (positive-going vs negative-going voltage to the rig). Different rigs expect different polarities — the X6100 expects negative ALC (the most common convention). TBD: verify the DIP-switch position for X6100-compatible ALC.
  • Band-data input format (open-collector vs 0-8 V analog vs serial CAT). Older Xiegu rigs used an analog band-voltage convention; newer ones use serial CAT.
  • Fan thermostat threshold: low/medium/high. Default medium.
  • Tuner enable/bypass at power-on: choose whether the tuner starts in bypass mode or active mode after a power cycle.

Once these are set for your station, leave them alone — they’re not session-level adjustments.

3.1.3 Firmware updates

The XPA125B exposes a USB serial port for firmware updates. Xiegu publishes occasional updates on their support site; the update tool is a Windows utility that uploads new firmware over USB. The process is similar to the X6100 firmware update procedure (Vol 9 §4 ↗) — connect USB, run the updater, wait for the progress bar.

Firmware updates are rare and not strictly necessary. The amp’s RF behavior is set by hardware (LDMOS finals, output network, tuner relays); firmware controls only the display, menus, and protection logic. Check Xiegu’s site once a year; otherwise don’t touch it.

For the broader programming-software view of the Xiegu ecosystem (X6100 + XPA125B + G90), see Vol 3 (Programming software).

3.2 Codeplug backups

Not applicable. The XPA125B holds no per-channel data, no per-frequency memories, no contact lists. The only state worth documenting is the DIP switch configuration, the menu-set ALC threshold and fan/VOX preferences, and the physical cabling setup between the amp and the X6100.

Document these in Scanners/programs/xiegu-xpa125b/notes.md (file pending the first bench setup session — placeholder for now). Items to capture:

  • DIP switch settings (each DIP position, on/off, with the function it controls)
  • Front-panel menu settings (ALC threshold value, fan mode, band-detect mode, RF-sense sensitivity, VOX hold)
  • ALC cable wiring: pin-out from XPA125B ALC OUT to X6100 ALC IN — the specific 3.5 mm TRS or DIN pinout, including which conductor carries the signal voltage and which is ground
  • CAT cable wiring: pin-out from XPA125B CAT to X6100 CAT — likely a 3.5 mm TRS or stereo cable
  • PTT cable wiring: pin-out from XPA125B PTT IN to X6100 PTT OUT
  • Power-supply cabling: which Powerpole or binding-post conductor is positive, which is negative, and the fuse rating (typically 25 A inline)
  • Heatsink temperature observed at idle, after a 10-minute SSB rag-chew, and after a 30-second key-down at 100 W (baseline for spotting future cooling degradation)

These aren’t a codeplug, but they are the operational state that a “rebuild the station from scratch” recovery would need.