Direction finding
A Direction finder turns an Array into bearings. Triangulation crosses bearings from several places, or from one moving array, into a position.
Set up
- Build and calibrate an Array, and wire a GPS to its
position. - Add Direction finder and wire the Array's
arrayto it. - Set Offset and Width to cover the signal.
- Pick a Method.
| Method | Use |
|---|---|
| Bartlett | Plain beam scan, robust |
| Capon | Sharper beam scan |
| MUSIC | Splits close sources |
| Root-MUSIC, ESPRIT | Grid free, need a line or a circle |
Sources counts transmitters with Auto, or takes a fixed number. Squelch drops weak peaks and Station names the bearings this finder sends. More holds the rest, such as Smooth against reflections and Yaw gate.
The rose
The rose shows the response around the array, each bearing, and its spread. Rel is relative to the array's forward direction. True is from true north and needs a heading or a fixed azimuth on the Array.
| Row | Shows |
|---|---|
| Bearing, ± | The strongest bearing and its one sigma |
| Fit | Share of the signal the bearings explain |
| SNR | Signal to noise |
| Src | Sources found |
| Chip | Means |
|---|---|
| Squelch | Peak below Squelch |
| No heading | Wire a GPS with heading to the Array |
| No position | Wire a GPS to the Array |
| Aliased | Antennas more than half a wavelength apart |
| Mode alias | Too high for phase modes on this circle |
| Mirror | A line cannot tell front from back. Side picks one. |
| Rotating | Turning faster than Yaw gate, blocks skipped |
| Singular | Covariance could not be inverted |
| Table off | Outside the calibration table |
| Stale | No reading for three report periods |
Listen in one direction
Wire the finder's bearing to a Beamformer steer input, and beam to
a channel.
Triangulate
- Add Triangulation and wire each finder's
eventsto it. - Give each finder's Array its own position. A moving array sends bearings from wherever it was.
A Signal hunt with a phone sends bearings too.
| Row | Shows |
|---|---|
| Estimate | The most likely position |
| Spread | The one sigma error ellipse |
| Guidance | Where to drive next: Drive across or Drive at it |
| Bearings | Bearings in use |
The table lists each station's last bearing, its spread, its learned heading offset and age. Align learns a constant heading offset per station, such as a turned array mount, once a loop or crossing pins it down. Fade sets how fast old bearings lose weight: Auto picks Fixed or Moving from the stations, Set takes your half life. Min conf refuses weak bearings and Emitters caps how many transmitters it finds. Clear throws away every bearing.
Wire a vehicle's GPS to Triangulation position for guidance. Guide picks Auto, which
crosses the bearings first and then drives at the fix, Direct or Off. Probe sets how
far to drive across a single bearing.
On the map
Wire finder and Triangulation events to a Map. It draws bearing rays, a heat layer of
likely positions, the estimate and its ellipse. The first fix is an event that an
Event output can forward.
In a car
Mount the array on the car, pair a phone and wire its GPS to the Array with Heading. The phone's DF drive mission shows the bearing and guidance and starts navigation to the target.
Bearings pause while the car turns fast; the phone shows Turning. Bearings taken when the signal suddenly drops, as behind a ridge where only an echo arrives, count less. Echoes still fool a single stretch of road: drive past from another side to confirm a fix.