What Is MLAT and What Does an ADS-B Feeder Need?

[Pavel]

Short answer: Multilateration estimates an aircraft position from time-difference-of-arrival measurements at several synchronized receivers. A feeder generally needs accurate time, stable continuous Mode S reception, correct approximate receiver coordinates and participation in a network with suitable neighbouring stations.

Before you start​

• Use 1090 MHz Mode S and ADS-B as the initial target unless the project specifically requires 978 MHz UAT in a region where it is used.
• Record antenna type and height, coax length, receiver gain, decoder version and a fixed observation window before comparing changes.

Step-by-step method​

1. Step 1: Build a stable local decoder first and verify Mode S messages from aircraft that may not broadcast position. MLAT cannot repair poor or intermittent reception.
2. Step 2: Set receiver location accurately enough for timing geometry but do not publish precise private coordinates on the forum. Supply them only through the feeder's protected configuration.
3. Step 3: Keep system time synchronized and follow the feeder network's supported timing method. Do not add arbitrary buffering or proxy layers that disturb timestamps.
4. Step 4: Check feeder status for synchronized peers and MLAT results. Dense station geometry and common aircraft visibility determine whether a local receiver can contribute.

Concrete example​

One receiver cannot determine a 3D MLAT position by itself. Several network receivers must observe the same Mode S transmission with compatible timestamps and geometry; improving message overlap can matter more than maximum single-station range.

How to judge the result​

A functioning feeder reports healthy timing, enough synchronized peers and generated MLAT positions when suitable traffic is present. Absence of results in a sparse region does not automatically mean local failure.

What to record​

• Compare unique aircraft, maximum range, messages per second and the shape of the polar coverage plot over equal time periods.
• Use at least 24 hours for a meaningful station baseline because traffic direction and density vary throughout the day.
• A higher message rate with fewer distant aircraft can indicate overload, local traffic changes or a different gain compromise rather than a universal improvement.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Publishing exact home coordinates or feeder credentials in a troubleshooting screenshot exposes information that is not needed for public diagnosis.

Final check​

Run the ADS-B station through another comparable observation window. Accept the change only when aircraft, messages and range metrics improve without overload, outages or exposed station credentials.