Direction finding
A Direction finder estimates a signal’s arrival direction from phase differences across a coherent array. It displays a bearing, confidence, and angular response so you can see competing peaks.
Wire one up
- Add a multi-lane Device, or an Array node for separate radios sharing a clock.
- Add a Direction finder. Set Geometry to your antenna layout: a circle with a radius, a line with element spacing, or explicit element positions. Set Elements to the antenna count.
- Connect every source lane to the corresponding
iq,iq2,iq3… input. All lanes must come from the same Device or Array. Applying an incomplete set of connections reports an error. - Connect a GPS position source to
positionto place bearings on a map or use triangulation. - Set Offset and Bandwidth to select the signal within the source’s tuned span.
Algorithm
| Algorithm | Behaviour |
|---|---|
| Beamformer | Broader angular response; useful as a baseline with limited covariance data |
| MUSIC | Sharper peaks; depends on an accurate source count |
Sources sets the number of arrivals MUSIC should assume. Start with one for a single source.
The compass and what it is telling you
The compass shows the angular response, selected bearing, and confidence. A strip below it shows calibration quality for each lane. Bearings run clockwise from north at 0°.
When calibration reports phase unknown, the node neither displays nor publishes a bearing. Check the array’s clock connections and calibration reference.
The beam output
The beam output sums the elements toward a selected bearing. Connect it to a channel to listen
in that direction.
| Beam | Behaviour |
|---|---|
| Follow bearing | Tracks the current estimated bearing |
| Fixed azimuth | Holds a chosen direction |
Switching to fixed azimuth starts at the beam’s current direction.
Crossing bearings from several finders
Add a Triangulation node and connect each Direction finder’s events output. Bearings from
different positions constrain the transmitter’s estimated location.
Each finder needs its own position source. Use GPS for a moving receiver, or a GPS position node with fixed latitude and longitude for a stationary one.
The Triangulation node shows the position estimate, error ellipse, guidance, and the age of each finder’s latest report. Clear resets the accumulated estimate.
A Direction finder works without triangulation, but then provides no position estimate, driving guidance, or event announcing a converged fix.
On the map
Connect a Direction finder’s events output to a Map to draw bearing rays that fade with age.
Connect Triangulation events to add the combined position estimate, uncertainty ellipse,
contributing stations, and suggested next waypoint.
Guidance
When the estimate has a long, narrow error ellipse, guidance suggests moving across the bearing to improve the intersection angle. Once the estimate converges, it switches to approach.
The first converged fix publishes a decoded event. Connected webhook, MQTT, or Matrix outputs can forward it. Use field mode for the phone interface and navigation.