Users say that the RTL-SDR stock antenna is useless. Not so. But close.
I have been using my RTL-SDR dongle to receive aircraft data on 1090 MHz. As part of the next generation air transportation system, aircraft broadcast ADS-B identification and positional data.
The RTL-SDR is a software defined radio. This is a re-purposed device. Originally designed for Europeans to receive digital television, it plugs into a USB port. DVB-T service is used in Europe, Africa and some parts of Asia-Pacific. Some hackers figured out how to make this little gem work as a software defined radio across a wide range of frequencies. Millions of these dongles have been sold for around $20 to radio listeners. A quite active community of enthusiasts finds all sorts of uses for them.
The problem with the RTL-SDR stock antenna is not just that it is cheaply made. It is. However, the real challenge is that the small antenna is designed for the digital television frequencies. These are in the 500 to 600 MHz range. This small antenna operates as something called a “vertical monopole” tuned to this range. Basically, this is a whip antenna a quarter-wavelength long. Vertical monopole antennas should be operated against a ground plane, which forms the other half of the antenna.
A Czech ham OH2FTG has analyzed these antennas. The results are shown in this video. Not surprisingly, the antenna works best on 500-600 MHz. There is some coverage above these frequencies, and nearly none below them. Fortunately, the ADS-B service lies in the range where there is some coverage.
RTL-SDR Stock Antenna ADS-B Range
Can you track aircraft with the RTL-SDR stock antenna? Surprisingly, yes, but not very far. Coverage data for eight hours is plotted on the map above as a grey area. The concentric circles are spaced at 20 nautical miles. The antenna is sitting on a table on the second floor of my house, near a window on the north side.
Generally, my ADS-B coverage is 30-40 nautical miles for aircraft at least 1000 feet above ground level. Occasionally, I receive signals from higher aircraft out to 50-60 nautical miles.
Is this good range? Not really. Most commercial aircraft use 100-250 watts of transmitting power. With a better antenna I should be receiving data out to 150 nautical miles. But the stock antenna is good enough for now. I will try building a better antenna soon.