Tune Your ADS-B Gain for Maximum Range

Watch it live while you tune

This is the ADSB IQ signal tuner. It plots message rate, RSSI, and your coverage centroid in real time — the exact numbers you watch to know whether a gain change helped or hurt. Feeders see this for their own station on the feeder dashboard.

Step 1 — Get the antenna right first

No gain setting rescues a badly placed antenna. 1090 MHz is line-of-sight, so height and a clear horizon beat everything else:

Higher is better. Roughly every extra meter of height adds about 2 nm of horizon. Rooftop > attic > window > desk.
Clear the horizon. Trees, walls, and terrain absorb 1090 MHz. One wall can cut your range in half.
Keep cable short. RG58 loses ~1 dB per 10 ft at 1090 MHz. Stay under 25 ft, or step up to LMR-400 for longer runs.

Full parts list and mounting walkthrough is in the Build Your Own ADS-B Receiver guide. Come back here once it's up and decoding.

Step 2 — Set your gain

The goal is the gain that gives you the most aircraft and the longest range without overloading the receiver. Too high and strong nearby signals distort; too low and you miss weak distant ones. On a typical wiedehopf readsb install, gain lives in /etc/default/readsb:

sudo nano /etc/default/readsb

Find DECODER_OPTIONS and set a gain value, e.g. --gain 43.9, then restart:

sudo systemctl restart readsb

The manual sweep

Start near the top (RTL-SDR max is ~49.6). Note your message rate and max range after ~10 minutes.
Step down through a few values (e.g. 49.6 → 44.5 → 40.2 → 36.4). Give each 10+ minutes.
Pick the gain with the best combination of aircraft seen, max range, and a healthy message rate — watch them on the tuner above.

Or let autogain do it

wiedehopf's autogain tool sweeps gain for you over a few hours and settles on a good value. If you installed readsb from his scripts, it's already available:

sudo systemctl restart readsb ; readsb-gain

In a strong-signal area? If you're near an airport or have aircraft directly overhead, lower gain often increases total range by preventing overload. Don't assume max gain is best — measure it.

Step 3 — Add a filter if you're in the city

Strong nearby transmitters can overload a wideband RTL-SDR. A documented 1090 MHz bandpass filter can reject out-of-band energy, but it cannot cure every interference source and adds some insertion loss. Add one only after measurements indicate overload, then compare results at the same times of day.

What good looks like

Placement	Typical max range
Indoor / window	Often 25–75 nm; building materials dominate
Attic	Often 50–125 nm; foil and metal roofing can block signals
Elevated outdoor, clear horizon	125+ nm is good; favorable sites may see farther

Once you're dialed in, feed it to ADSB IQ and see your live range, RSSI, and rank. Already feeding elsewhere? Add ADSB IQ in one line — it uses the same receiver you just tuned.

→ Go to your feeder dashboard