Also known as: 1090 MHz antenna, flight tracking antenna, Mode S antenna
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An ADS-B antenna is a vertical antenna tuned to 1090 MHz, the frequency on which aircraft broadcast their position, altitude, and identity via ADS-B (Automatic Dependent Surveillance–Broadcast). Paired with an RTL-SDR and decoder software such as dump1090, it turns a cheap dongle into a live flight tracker. Like any resonant antenna it hands the receiver far more signal at its design frequency than a generic wideband whip, and because 1090 MHz has a wavelength of only about 27 cm, a proper ADS-B antenna is small, cheap, and easy to mount high.
How it works
ADS-B is an unencrypted, open broadcast: transponder-equipped aircraft transmit a Mode S Extended Squitter at 1090 MHz roughly once a second, and anyone with a 1090 MHz receiver can decode it — there is nothing to break into, unlike the encrypted land-mobile traffic a scanner sometimes hits. The antenna’s whole job is to capture as much of that faint downlink as possible.
Most ADS-B antennas are gain verticals — a collinear stack of co-phased elements that squeezes the pattern toward the horizon, which is exactly where distant aircraft sit relative to a rooftop antenna. They are omnidirectional in azimuth, so they hear planes from every bearing, and they are cut sharply for the narrow 1090 MHz band, giving them a big edge over the broad, unresonant whip that ships with a dongle. Some antennas are dual-band 1090/978 MHz, adding the US-only UAT link used by general aviation and for FIS-B weather and TIS-B traffic uplinks.
Two install facts dominate ADS-B range:
- Height and line of sight. At 1090 MHz reception is essentially line-of-sight to the radio horizon, so every extra foot of antenna height and every obstruction removed adds coverage. A clear rooftop mount routinely reaches 100–250 miles to high-altitude airliners.
- Coax loss is severe. At 1 GHz, cable attenuation is high, so a long thin feedline can waste most of the signal. Keep the coax run short and thick, or — better — mount a low-noise amplifier and a 1090 MHz band-pass filter at the antenna so gain and selectivity are applied before the cable loss and before strong cellular/FM signals can desensitize the SDR.
Relevance to SDR
ADS-B is one of the most popular first projects for an SDR: an inexpensive RTL-SDR, a 1090 MHz antenna, and dump1090 or a similar decoder produce a live map of aircraft overhead. It is a different application from GopherTrunk — GT decodes VHF/UHF land-mobile voice trunking, not the 1090 MHz aircraft data link — but the hardware philosophy is identical: a resonant antenna matched to the target frequency, mounted high with a short low-loss feed, is what separates a toy setup from one that hears distant signals. Many GopherTrunk users run an ADS-B receiver on the same bench or the same Raspberry Pi, which is why the antenna is documented here.
Where to buy
For flight tracking, a purpose-built FlightAware 1090/978 MHz ADS-B antenna (around $65) is the standard upgrade over a dongle’s stock whip: a gain vertical resonant right at 1090 MHz, with an N connector and a coax run for a masthead mount. Put it as high and clear as you can, keep the feedline short, and add a 1090 MHz filter/LNA at the antenna if strong local signals are desensitizing the receiver.
For the decoding side, see ADS-B, Mode S, and dump1090; for the RF budget, the low-noise amplifier and coaxial cable pages.
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Sources
Frequently asked questions
Which antenna should I buy for ADS-B flight tracking?
A purpose-built 1090 MHz antenna such as the FlightAware ADS-B antenna (around $65) is the standard pick: it is a gain vertical resonant right at 1090 MHz, so it dramatically outperforms the wideband whip that ships with an SDR dongle. Mount it as high and clear as you can and keep the coax short — at 1 GHz, cable loss is brutal, so a masthead-mounted antenna with a short low-loss feed (or an LNA at the antenna) is what pulls in distant aircraft.
Do I need a special antenna, or will my dongle's whip work?
A stock whip works for nearby aircraft, but a resonant 1090 MHz antenna is a large upgrade for range. ADS-B lives at 1090 MHz, far above the bands a generic telescopic whip is optimized for, and because the wavelength is only about 27 cm, a proper 1090 antenna is small, cheap, and easy to mount high. Height plus a resonant antenna plus short coax is the recipe for tracking planes 100–250 miles out.
What is the difference between 1090 MHz and 978 MHz for ADS-B?
1090 MHz (Mode S Extended Squitter) is the worldwide ADS-B frequency used by airliners and most aircraft. 978 MHz (UAT) is a US-only link used mainly by general aviation below 18,000 feet and also carries free weather and traffic uplinks (FIS-B/TIS-B). A 1090-tuned antenna is the priority; some dual-band antennas cover both, which is handy in the US if you also want UAT.
Should I add a filter or LNA for ADS-B?
Often yes. Strong nearby cellular and FM signals can desensitize a wideband SDR at 1090 MHz, so a 1090 MHz band-pass filter (and a low-noise amplifier at the antenna to overcome coax loss) is a common and effective addition. Mount the LNA at the antenna so its gain is applied before the cable loss, per the Friis budget. Many ADS-B ‘pro’ dongles bundle the filter in.