January 27, 2018


Last edited: 27.01.2018

This is my latest high tech creation, hi. It's a little 4-leg "spider" antenna for 1090 MHz (1.090 GHz) constructed around a nice old Amphenol SO-239 chassis connector that I had lying around. Its 4 legs and top element are made from copper wire and are about 68 mm in length.

Beside being a ham radio operator, I've always been a radio hobbyist in general, and every once in a while I like to explore radio related stuff outside of the ham bands. The little spider antenna is used to receive the ADS-B signals broadcasted from aircraft on 1090 MHz. ADS-B stands for Automatic Dependent Surveillance - Broadcast. ADS-B signals are periodically (twice every second according to the YouTube movie below) broadcasted by aircraft and contain among other things the aircraft's unique ICAO identifier, the aircraft's callsign, and data provided by the GPS navigation system of the aircraft, like GPS location, altitude, heading, speed, etc. ADS-B signals enable an aircraft to be tracked in real-time by for instance air traffic control stations. Since other aircraft can also receive the ADS-B signals from ADS-B equipped aircraft surrounding them, it also provides pilots with improved situational awareness.

I use my RSP1A SDR receiver (see my last blog entry) connected to the spider antenna to receive the ADS-B signals. Special software extracts the data from the signals. This data is sent to another computer program called Virtual Radar Server (VRS) which then plots the received aircraft on a map. With the aircraft identifiers received on 1090 MHz, VRS is able to retrieve additional information for the aircraft from various online databases, including the aircraft registration or "tail number" and the current route (destination and departure airport). When you select an aircraft, VRS also shows the aircraft type and model, operator, country of registration, and when available (most of the time) even photos of the aircraft (not just a random photo of the type and model, but the actual aircraft with the registration of the selected aircraft).

It's really fun to see in real-time what's up in the airspace above you. Of course you can also use some online service like www.flightradar24.com for this, but for the radio hobbyist it's a thrill to know that the aircraft that are plotted on the map are plotted there because their ADS-B signals have been received with his own radio equipment directly over the air.
With the antenna inside the house, depending on the height I place the antenna at (ground level or attic), I've been receiving aircraft up to distances of 100 to 200 km. You can even do some DXing, trying to catch aircraft from as far away as possible and trying to beat your personal record.

The ADS-B data extracted from the signals received on 1090 MHz
The aircraft plotted in Virtual Radar Server. For the selected aircraft (the one in yellow) additional information is displayed, including route, operator, country of registration, tail number, aircraft type and model, and any available photos of the aircraft.

Below some YouTube movies explaining how to set up ADS-B with your SDRPlay RSPA1/1A/2 receiver and explaining how ADS-B works.

See also:


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