Passive radar
Passive radar compares a broadcast transmitter's direct signal with its echoes off aircraft. It measures how much further each echo travelled and its Doppler shift. Two lanes on a shared clock are enough. Phase calibration is only needed for echo bearings.
Wire it
- Build an Array with at least two lanes, tuned Together.
- Add Passive radar and wire the Array's
arrayto it. - Point one antenna at the transmitter and pick its lane under Ref. Listen picks the lanes that hear echoes: Others or Pick.
- For the map, wire a GPS to the Array, and a GPS set to Fixed at the transmitter to
tx. - Optional: wire an ADS-B channel's
eventstotruth. Tracks that match an aircraft show its call sign.
Illuminators
Pick one under Illum.
| Illuminator | Notes |
|---|---|
| FM | Strongest echoes. Clean with CMA removes the programme's multipath. |
| DAB | Wider band, finer range. Clean with DAB remod rebuilds a clean reference. |
| DVB-T | Uses the slice of the channel the lanes cover, set by Bandwidth |
| Custom | Any signal, with your own Bandwidth |
Offset is the transmitter's frequency minus the Array's centre.
Read the view
The plot shows bistatic range against Doppler. Bright cells are echoes; detections are marked. An echo seen over several looks becomes a track in the table: range, speed, bearing, SNR and the matched ADS-B aircraft. A single flash is often noise.
| Readout | Shows |
|---|---|
| Targets | Confirmed tracks |
| Clutter | Direct path and clutter removed |
| Load | Share of real time spent |
| Ref | Reference quality: Raw, Lost, or CMA or DAB with its dB |
| CPI | Integration time in use |
| Drops | Lost samples or looks, shown when not zero |
Clear forgets every track. The phone's Radar mission shows the same view.
The range is bistatic: the extra distance the echo travelled compared with the direct path. One echo gives an ellipse on the map, not a point. A tracked echo with a bearing, or an ADS-B match, gets a position.
Settings
| Setting | Does |
|---|---|
| Range | How far out and how fast (Speed) to search |
| CPI | Integration time. Longer finds weaker echoes but blurs fast ones. Overlap reuses part of each. |
| AoA | Bearing per echo. Needs a calibrated array. |
| GPU | Auto uses the GPU when it is faster |
| Clutter | How the direct path and ground clutter are removed: ECA-B, ECA-S, NLMS, Block NLMS or Off |
| Pfa | False alarm chance per cell |
| Detect | The CFAR detector (CA, OS or GO) and Min SNR |
| Track | Hits over looks that start a track (Start hits, Start looks), and misses that end it (Coast) |
Limits
- The lanes must see the transmitter and the sky. A strong direct path in the surveillance antennas limits range.
No transmitterorNo array position: wire the GPS nodes from step 4.Overloadedmeans the host cannot keep up: shorten Range or CPI, or set GPU to Auto.Outside cal tablemeans the Array's measured table does not cover the carrier. Bearings then use the ideal geometry.- A lane rate below the illuminator's bandwidth cuts range resolution.