Best 1090 MHz Antenna Placement for ADS-B

[Pavel]

Short answer: Place a vertically polarized 1090 MHz antenna outdoors, as high as safely practical, with a clear horizon and short low-loss coax. ADS-B is largely line-of-sight, so obstructions and feedline loss usually matter more than small changes in antenna gain.

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: Map nearby buildings, roof lines, trees and metalwork. Choose a position with the widest unobstructed azimuth rather than simply the highest indoor shelf.
2. Step 2: Keep the antenna vertical and away from metal poles unless its design uses them. Route coax with weatherproof connectors, strain relief and a drip loop.
3. Step 3: Estimate cable loss at 1090 MHz. If a long run is unavoidable, use lower-loss coax or a suitable filtered antenna-side LNA powered safely.
4. Step 4: Record a 24-hour baseline before and after moving the antenna with unchanged decoder gain. Compare polar plots, aircraft and message counts by direction.

Concrete example​

Moving an antenna from an upstairs window to a roof position may improve one blocked direction dramatically even with the same coax. Replacing 10 m of lossy small coax can recover several decibels without changing the antenna.

How to judge the result​

The best placement improves the coverage plot across repeatable directions and increases valid messages over full-day comparisons. One exceptional aircraft is not enough evidence.

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.
• Mounting directly beside a metal mast or under a conductive roof can distort the pattern and erase the benefit of extra height.

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.