Comparison: RadarBox FlightStick/Antenna vs FlightAware Pro Stick Plus/Antenna

[hletrd]

I’ve installed 2 ADS-B receiver sets onto the rooftop together, side-by-side to make a brief performance comparison between two hardwares.

Set #1 (Left, white antenna): AirNav RadarBox 1090MHz antenna (7dBi), RadarBox FlightStick, with a RadarBox 1090MHz bandpass filter. A 30ft 3D-FB non-user-replacable antenna cable, provided with the antenna was used.

Set #2 (Right, dark green antenna) FlightAware 1090MHz antenna (5.5dBi), FlightAware Pro Stick Plus, with a FlightAware 1090MHz/978MHz bandpass filter. A 3m 5D-FB antenna cable was used.

I used 2 Raspberry Pi 4 B+ with the latest PiAware 6.1 / dump1090-fa installed, and automatic gain control is enabled.

The RadarBox antenna is an active antenna with integrated filter and LNA, probably powered by the bias tee. According to the specifications, the antenna has an integrated 1090MHz BPF and an LNA with 20.5dB gain. A 30ft non user-replacable 3D-FB cable is provided together, which shows about 3-4dB attenuation for 1090MHz signals according to the specifications.

The FlightAware antenna is a passive antenna, looks pretty similar at the same dimensions with the RB antenna. The antenna uses the type N connector, which renders the cable user-replacable. The cable I used is a 5D-FB cable with 3m length, which shows under a dB of attenuation for 1090MHz according to the specifications.

2 antennas are installed about 1.5m apart from each other to minimize the interference. The measurement was done in south of Seoul, South Korea. The site suffers from a strong out-of-band signals, mainly due to the FM/TV broadcast stations, located at about 2km from the site. (The broadcast station is visible at the center of the first picture.) There are tens of FM transmitters (~10kW), and a few ATSC transmitters (~5kW) installed.

Here are the initial results:

• FA antenna with FA Pro Stick Plus
  Because the Pro Stick Plus have a LNA directly connected to the antenna input, it seems to be easily saturated by the strong out-of-band signals.

• RB antenna with RB FlightStick
  According to this post, it seems that a 1090MHz SAW filter is placed just after the antenna input, before the LNA.

• FA antenna, with FA 978MHz+1090MHz BPF and FA Pro Stick Plus
  FA BPF works extremely well to filter out the undesired signals, therefore improving the reception drastically.

• RB antenna, with RTL-SDR.com FM rejection filter and RB FlightStick. The internal filter of the antenna seems to work reasonably well to filter out undesired signals, thus the FM rejection filter does not significantly improve the reception.

• FA stick, with RTL-SDR.com FM rejection filter
  The FM rejection filter also worked quite well to filter the strong FM signals from the nearby towers.

• RB antenna, with RB 1090MHz BPF and
  RB FlightStick
  RB 1090MHz BPF actually DEGRADED the reception with RB flightstick and RB antenna. Probably it disables the integrated LNA in the RB antenna (which is supplied by the bias tee from the USB stick) by blocking DC?

I’m still trying some more configurations.

[foxhunter]

Seem to be that the gain is too high on all your combinations.
Depending on your location the number of strong messages (Messages > -3dBFS) should be targeted to around 5% maximum.

We made an upgrade the other day on one of our feeders on a church tower. Initially it was only a blue FA stick, we upgraded it with a better antenna and an Uputronics LNA with filter.

Without reducing the gain significantly, the stick was simply overloaded and was not able to deliver any good result. Only by changing the gain (done via try&error) we were able to get the optimal settings for it.

[hellhound604]

not knowing where the (RF) bottom of those 2 antennas actually are, I would raise them both by about 1m on vertical poles and redo the measurements. Any antenna long in comparison with the wavelength (27cm in our case) suffer more from distortion of their radiation-lobes than electrically short antennas (our friend, the 1/4 antenna). You have separated them a bit horizontally, but both are still quite close to that horizontal poles.
ideally you should do the sums, or use a calculator(Antenna Near Field & Far Field Distance Calculator | Southwest Antennas - High Performance RF and Microwave Antennas & Custom Antenna Manufacturing) to calculate what distance the antennas should be from each other and other surfaces, and only then you can make true measurements, taking into account that by seperating them other obstacles can come into play.