Rotor Server for N1MM and More!

📝 Background

This software was written for the club and contest station PI4RCK / PA6Y in the Netherlands. The station runs multiple directional antennas on rotors and sits in a notoriously exposed location. When the wind picks up in this part of the country, it picks up fast — and with several large Yagi antennas mounted on masts, the question is not whether the wind will be a problem, but when.

After a few uncomfortable situations during storm alerts — manually checking and rotating antennas in the middle of the night, or during a contest when nobody has time for it — it became clear that a proper software solution was needed. Something that would watch the wind continuously, and move the antennas to a safe position automatically when conditions got bad, while still allowing full N1MM Logger+ control the rest of the time.

The result is N1MM Rotor Server: a Linux-based rotor controller that is fully compatible with N1MM Logger+, adds a live graphical interface, and includes an integrated wind monitor with automatic storm protection — built around the real-world needs of an active contest station.

N1MM Rotor Server is an antenna rotor controller for Linux, designed to work seamlessly with N1MM Logger+. It runs on virtually any machine with Debian Trixie — from a small Raspberry Pi tucked away in the shack to a regular desktop PC — supports multiple rotors simultaneously, and includes a real-time GTK4 graphical interface, a wind monitor, and automatic storm protection.

🔗 100% compatible with N1MM Logger+

N1MM Rotor Server speaks exactly the same protocol as the rotor server built into N1MM Logger+ — the same UDP port, the same XML command format, the same heading broadcast. From N1MM’s perspective there is no difference: it sends GOTO commands and receives position updates just as it always did.

What is different is everything around it. Where the built-in N1MM rotor server is a basic Windows-only tool with minimal feedback, N1MM Rotor Server adds:

• A live graphical interface with compass roses and real-time position display
• Support for up to 16 rotors running simultaneously
• A wind monitor with multiple data sources
• Automatic storm protection — antennas move to safety when the wind picks up
• A heading offset per rotor to compensate for mechanical misalignment
• Automatic USB reconnect when a cable is unplugged

You simply point N1MM Logger+ at the new server’s IP address — nothing else changes in your contest setup.

🔌 Features at a glance

🔧 Supported hardware

Rotors connect via USB-to-serial adapters and are identified by USB port position (stable by-path symlinks), so the device assignment never changes even when adapters are swapped.

💻 The GUI

The graphical interface (n1mm_rotor_gui) runs as a normal user alongside the server and connects to it automatically via a local Unix socket — no IP address or port configuration needed.

Rotor card

Each rotor gets its own card with a Cairo-drawn compass rose. The orange needle shows the current azimuth, the dashed blue line shows the target. When a heading offset is configured it appears as text inside the compass (e.g. Offset: −10°). During storm mode a colour-coded lock icon appears: green = free, red = GOTO blocked.

Click anywhere on the compass to send a GOTO command directly to that rotor.

Wind Monitor card

The top-left card always shows live wind data: direction in degrees and compass point, force in Beaufort, gust speed in m/s, the configured storm threshold and a countdown timer. The status indicator at the top switches from green (Normal operation) to orange (Storm correction active) when the sustain timer fires. The large button at the bottom activates or deactivates storm mode with a single click.

Wind Rose card

Directly below the Wind Monitor sits a dedicated compass showing the current wind direction as a solid blue arrow. The tail points to the wind source on the compass perimeter; the tip points toward the centre. When no data is available the rose is greyed out.

Multi Control card

The Multi Control card lets you point all rotors to the same azimuth with a single click — useful at the start of a contest when you want every antenna beaming the same direction, or during a pile-up when you rotate the whole station at once. A red exclamation icon and a warning banner make it impossible to accidentally trigger: you always know exactly what you are about to do.

The Multi Control card respects the same storm blocking rules as individual rotors — if a rotor has GOTO blocked due to active storm correction, the multi-control move will not override it unless that rotor is marked as always controllable.

Configurable layout

The number of grid columns is freely adjustable from 1 to 8 via the settings dialog. The Wind Monitor and Wind Rose always occupy the top-left corner; all other cards fill in from there.

🌡 Wind Monitor

The wind monitor runs as a background thread and broadcasts wind data every second over a local UDP port. The GUI receives it in real time.

Supported wind sources

Internet sources — Open-Meteo, Yr.no and more

The simplest way to get started: select Internet as the source type, choose Open-Meteo from the service list, enter your latitude and longitude, and set a fetch interval. The server retrieves forecast wind data automatically — no account, no API key, no subscription.

Ecowitt — live data from your own weather station

If you have an Ecowitt (or compatible) weather station, select Ecowitt (HTTP) as the source. Configure the station in the WS View app to push data to the server’s IP address and port. Wind data then arrives in real time every 16–60 seconds — far more responsive than polling an internet service.

The server can also forward every received push to a second destination — for example a WordPress weather plugin — over HTTP or HTTPS. The station’s PASSKEY is shown automatically in the Station PASSKEY field as soon as the first push arrives, so you can copy it straight into your plugin’s settings without hunting for it elsewhere.

⛈ Storm Mode

Storm mode is the core reason this software was built. It watches the wind continuously and moves antennas to a safe position automatically — without any human intervention — the moment conditions become dangerous.

How it works

1. You activate storm mode once via the ACTIVATE button in the GUI. The server now watches the wind.
2. When the wind force exceeds the configured Beaufort threshold and stays above it for the sustain duration, correction begins. The sustain timer prevents a single gust from triggering unnecessary movement.
3. Every storm-enabled rotor is driven to its calculated safe azimuth. N1MM Logger GOTO commands are blocked while correction is active (configurable per rotor).
4. The server re-sends the GOTO at a configurable interval (e.g. every 15 minutes) so the antenna stays on target even if the wind direction shifts.
5. When the wind drops below the threshold for the release duration, correction stops and normal operation resumes. The release timer prevents premature return during a lull.

Storm mode state (on/off) is saved to the config file and survives server restarts — if the server reboots during a storm, it comes back up in exactly the same state.

Per-antenna storm offset

Not every antenna needs to face the same direction in a storm. Each rotor has its own storm offset — a value in degrees relative to the wind direction — so you can position each antenna optimally for its mechanical characteristics:

Shortest-path rotation — mechanical stop aware

Rotors have a mechanical stop, typically somewhere around 0°/360°. Driving an antenna the long way around across the stop not only wastes time but can damage the rotor cable. N1MM Rotor Server avoids this automatically.

For every correction move, the server calculates two candidate positions — the primary target and its mirror 180° away (which is always an equally valid safe position, since both put the antenna edge-on or head-on to the wind). It then picks whichever one the rotor can reach via the shortest arc, never crossing the mechanical stop:

• Example: wind is from 10°, storm offset is 0° (head into wind). Target = 10°. If the rotor is currently at 330°, the direct path is only 40° away — but it crosses 0°/360°. The server automatically flips to the mirror position at 190°, which the rotor reaches in 140° without ever crossing the stop. ✓

This logic runs silently every time a correction is applied, so you never have to think about it — the antenna always takes the safe route.

System flow

Storm settings summary

• Threshold (Bft) — wind force that triggers the sustain timer
• Sustain before on — minutes above threshold before correction starts
• Sustain before off — minutes below threshold before correction stops
• Correction interval — how often the GOTO is re-sent during active correction
• Block manual GOTO — globally prevent N1MM from overriding the safe position
• Always controllable — per-rotor override: this rotor always responds to N1MM, even during storm correction
• Storm offset — per-rotor angle relative to wind direction (−180° to +180°)

💻 Installation

N1MM Rotor Server runs on virtually any machine with Debian Trixie installed — a Raspberry Pi 4 or 5 tucked away in the shack is a popular choice, but a regular PC or mini-PC running Debian works equally well. The only requirement is a desktop environment for the GUI.

Download the source and run the installer:

sudo bash install.sh

The installer takes care of everything in one go:

• Installs all build dependencies automatically
• Compiles and installs the server and GUI binaries
• Creates the configuration directory and default config file
• Creates the log file at /var/log/n1mm_rotor_server.log with correct permissions
• Registers a systemd service so the server starts automatically on boot
• Grants serial port access for rotor communication

After installation, log out and back in once (to activate group changes), then launch the GUI:

n1mm_rotor_gui

Configuration via the GUI

All further configuration is done through the graphical interface — no manual editing of config files is needed. The GUI settings dialog covers everything:

• Rotors — add, edit or remove rotors; select protocol, serial port, baud rate and heading offset
• Server — ports, broadcast addresses and timing intervals
• Wind — wind source, location, Ecowitt settings, forwarding and all storm parameters

The server is started and stopped directly from the GUI. Configuration changes take effect after a server restart, which the GUI prompts you to do automatically.

GOTO blocking — keeping antennas safe during a contest

One of the more subtle challenges with storm protection during a contest is the tension between safety and operability. The storm protection moves an antenna to a safe position — but N1MM Logger+ may immediately send a GOTO command to rotate it back to the working direction. Without any blocking, the protection would be undone within seconds.

N1MM Rotor Server resolves this with a three-level blocking system:

In practice a typical setup looks like this: all large Yagis have Block manual GOTO enabled and Always controllable off — they are fully protected. A smaller antenna that is mechanically less critical might have Always controllable on, so it still follows N1MM during a contest even when the storm system is active.

Lock icons — status at a glance

While storm mode is active, each rotor card shows a colour-coded lock icon inside the compass rose so the operator can see the situation immediately without opening any dialog:

When storm mode is not active, no lock icons are shown — the compass roses remain clean and uncluttered.

⚙ Server settings

All server parameters are set in the GUI settings dialog. The command port (12040) and primary broadcast port (13010) match the N1MM Logger standard. A secondary broadcast port can be added for a second client — useful if you want both N1MM and a separate display tool receiving position updates simultaneously. Multiple broadcast addresses are supported, comma-separated.

⚙ N1MM Logger+ configuration

In N1MM Logger+, go to Config → Configure Ports, Mode Control, Winkey, etc. and open the Rotor tab:

• Rotor type: N1MM Rotor
• IP address: IP of the machine running the server
• Port: 13010 (receive) / 12040 (send)
• Rotor name: must match exactly the name configured in the server

The server reports heading as azimuth × 10 (e.g. 180.0° = 1800), which is the N1MM standard format.

📝 Technical details

Architecture

• Single C source file (n1mm_rotor_server.c), compiled with gcc -std=c99
• Multithreaded: UDP receiver, poll/broadcast, wind monitor, storm monitor, GUI server
• GUI communicates via Unix domain socket — no network configuration needed
• Broadcast timing adapts per rotor: fast (200 ms) while moving, slow (1 s) when idle
• Stall detection: if azimuth doesn’t change by ≥ 5° within 5 s, the rotor is considered stalled and returns to idle timing

Broadcast protocol

• Receive (N1MM → server): XML on UDP port 12040
• Send (server → N1MM): NAME @ heading on UDP port 13010
• Secondary broadcast port (13011–13015) supported for additional clients
• Multiple broadcast destination addresses supported

Log file

All server events are logged to /var/log/n1mm_rotor_server.log. The GUI includes a log viewer that follows the file in real time.

📄 License & source

N1MM Rotor Server is developed by Björn Pasteuning — PD5DJ.

• 🌐 www.pd5dj.nl

© 2024–2026 Björn Pasteuning — PD5DJ