ADS-B 1090 LNA
27 dB preamplifier and filter for the 1090 MHz ADS-B frequency powered by bias-tee
This LNA can help improve ADS-B reception by reducing the system's noise figure and helping to overcome losses in the coaxial cable and/or other components such as switches and connectors in the signal path. To get the best performance from an LNA, the LNA should be placed immediately after the antenna, before the coaxial cable run to the radio.
The gain of this LNA is 27 dB at 1090 MHz, while out-of-band signals are reduced by at least 60 - 80 dB. The attenuation of the FM band and everything below 800 MHz is over 100 dB. In the LNA signal path, there is first a low insertion loss high-pass filter that reduces the power of any FM, TV, pager, or other similar transmissions that are usually extremely strong. Then between the first and second stages of the LNA is a SAW filter tuned for 1090 MHz. A second SAW filter is on the output of the LNA. The result is that strong out-of-band signals are significantly blocked, yet the LNA remains effective at 1090 MHz with an NF value of approximately 1 dB.
The LNA is also protected from ESD damage with a gas tube and a low capacitance ESD diode. But always remember that the antenna must be properly grounded to prevent ESD damage.
Please note that this LNA requires bias tee operation. Bias tee voltage is when DC current passes through the coaxial cable. RTL-SDR V3 has built-in bias tee and can be activated in the software. See the V3 user guide for information on how to activate it. Alternatively, if you do not own a dongle with an integrated bias tee, you can use an external bias-tee which can be found on eBay quite cheaply. Finally, if you are good at soldering SMT components, there are pads and a slot for a 0 Ohm resistor on the PCB to install an LDO and power the LNA directly.
Also, remember that this is a high-gain LNA. It should be used on the antenna side, with an expected loss of 3+ dB on the coaxial cable. However, if desired, it can still be used on the receiver side. If used on the receiver side or with low coaxial cable loss, you will need to adjust the RF gain on the RTL-SDR dongle. By default, most software sets the RF gain to maximum. We recommend setting the RTL-SDR RF gain to about 32 dB if you connect it directly to the dongle, otherwise, the high input power could overload the dongle causing poor performance.
