An active antenna is a type of antenna that includes an electronic amplifier to boost the signal it receives. This design contrasts with passive antennas, which do not include any electronic components to enhance the signal.
Active antennas are widely used in scenarios where receiving a strong signal is challenging yet critical.
In this post we discuss how to build an active antenna for ADS-B signal reception using off-the-shelf parts (no soldering required).
Table of Contents
ADS-B Frequency Range
Automatic Dependent Surveillance-Broadcast (ADS-B) primarily operates on the 1090 MHz frequency band. This is referred to as the 1090 Extended Squitter (1090 ES), and it’s the international standard for ADS-B transmissions used by most aircraft, particularly those operating above 18,000 feet.
There is also a secondary frequency used for ADS-B, known as 978 MHz, under the UAT (Universal Access Transceiver) protocol. This is primarily used in the United States for aircraft flying below 18,000 feet. The UAT protocol provides services like traffic information, weather updates, and other flight information, in addition to the ADS-B capabilities.
Antennas for ADS-B
In this post we discussed some of the antenna options for ADS-B. These are passive antennas.
A key feature of an active antennas is amplification to boost weak signals it receives. This can be particularly useful in environments where signal strength is poor, such as in remote areas or for frequencies that are difficult to capture reliably.
Since the antenna does not have a built-in amp, we can add one to it.
Here are some options.
Amplifier Options
There are three different Low Noise Amplifier (LNA) options
15 dB Gain @ 1090 MHz
A 15 dB gain amp is used to boost the 1090 MHz ADS-B signal by a factor of 30.
It includes an ADS-B filter that rejects signals outside of this band.
30 dB Gain @ 1090 MHz
A 30 dB gain amp is used to boost the 1090 MHz ADS-B signal by a factor of 1000.
It includes an ADS-B filter that rejects signals outside of this band.
The pros of this high gain amp is that it can amplify signals from very far away. The cons are that it will boost relatively strong signals to a point where it might saturate the ADS-B receiver. Here are tips on optimizing the signal levels into your receiver.
14 dB Gain @ 978 MHz and 1090 MHz
This 14 dB gain amp boosts signals at both (UAT) 978 MHz and 1090 MHz.
It includes a 978 to 1090 MHz bandpass filter that rejects signals outside of this band.
Which Amplifier to use?
It’s very difficult to predict the amount of gain that’s required in any particular environment. As a result you will have to experiment.
If you want to receive signals in the 1090 MHz band only, we recommend going with the 30 dB LNA and some RF attenuators as the signal levels might have to be adjusted. That’s been our experience across a wide range of signal environments.
Power Requirements
Active antennas require a power source to operate the amplifier. This power can be supplied through a separate power cable, via the antenna cable (as in Bias-T power), or through batteries.
The advantage of a Bias T approach is that the noise figure is minimized and the sensitivity is improved to a point where you can see planes that are very far away.
Here are the Bias T options associated with the amps presented above
- 15 dB 1090 MHz LNA with Bias T
- 30 dB 1090 MHz LNA with Bias T
- 14 dB 978 + 1090 MHz LNA with Bias T
Results
The picture below shows results when a 30 dB LNA with a Bias T is used. It results in a tripling of the number of aircraft observations.
Summary
Overall, active antennas are valuable for enhancing signal reception in challenging conditions, making them essential tools in both amateur and professional radio communication contexts.
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