Hello everybody! I have a question that has been taking my patience away for a while. I have noticed that in some situations where, even with a good or reasonable signal, my flightfeeder does not receive the aircraft positions. I don’t know what to do to resolve this, if it’s even possible. Has anyone gone through this?
Sometimes it happens that the aircraft disappears for a while and then reappears, leaving a dashed line in the skyaware. That’s right with a good signal…
Obrigado Jonhawkes2030. There is no obstruction. The sky is clear around the antenna.
In the first image the signal is at -2.4dBFS. In the second photo I didn’t pay attention to the signal level, but it was certainly good as the distance was less than 7 miles during much of the dotted route. This type of situation happens a few times a day, with some aircraft, not all…
I have a question: can the position of the aircraft during flight obstruct the signal between it and the flightaware antenna? Where is the antenna that transmits the ADS-B signal on aircraft?
“Existing standards mandate that all aircraft with a maximum take-off weight of more than 5 700 kg, as well as smaller aircraft capable of maximum cruising speed of 324 km/h (175 kts) or greater and/or cruising altitudes of 15 000 feet (4.6 km) or higher, carry two antennae transmitting the ADS-B signal at 1 090 MHz (one placed on the bottom and one placed on top of the fuselage) in order to enjoy the benefits of antenna discrimination.”
The dropouts you see are probably due to multipath.
Sorry, I did not open the picture so missed the db reading. -2.4dBFS if very strong.
You may want to lower your gain setting to see closer aircraft. This may also mean that you lose distant aircraft. This is a limitation of the dynamic range of the USB Dongle.
In other words, you are probably receiving a signal that has taken more than one path to your receiver. The multiple paths could be produced by nearby buildings or other objects or terrain. The two (or more) received paths can then result in constructive or destructive interference of the received signal. If it’s destructive interference, the received signal is too weak to be received.
With my setup, where the antenna is in the attic, I have observed many times that aircraft will fade in and out several times while on a straight and level course or ascending or descending. These aircraft are at a sufficient altitude and distance that the signal is not too strong and overloading the receiver.
Regarding whether the problem is due to the antenna placement on the aircraft, there are two antennas on the aircraft: top and bottom. A terrestrial receiver would normally be receiving a signal from the bottom antenna. However, there could be situations, say in a turn, where the bottom antenna is shadowed by an aircraft wing. In that case you could still receive from the top antenna (although with some polarization loss since the aircraft antenna is not vertical any more). However I have never seen dropouts in a turn, but always with the aircraft flying in a straight line as stated above.
So, in conclusion, I think the problem is due to multipath.
“In other words, you are probably receiving a signal that has taken more than one path to your receiver. The multiple paths could be produced by nearby buildings or other objects or terrain. The two (or more) received paths can then result in constructive or destructive interference of the received signal. If it’s destructive interference, the received signal is too weak to be received.”
I decided to reduce the radio gain of the flightfeeder from 50 to 43. And apparently there was no reduction in range, but the signal levels in dBFS dropped significantly. For example, this flight KLM701, never got below -15 dBFS (despite the equivalent distance of 270 nautical miles) and now they are at -22 dBFS… Could this reduce the number of messages received? I intend to keep this configuration for a few days and evaluate.
Yes. And the biggest difference between what you see and what a nearby site sees is in the number of positions reported rather than number of aircraft reported. At least that’s what I have observed. Don’t know if you have a lot of nearby sites to compare.
Yes! I am monitoring the message logs of 3 stations near mine. One of them receives half of my ADSB positions and the other receives approximately 6,000 positions less daily.
My average number of aircraft varies a lot, with a high of around 100-150 aircraft per day. I know that’s not a lot when compared to geographic regions with higher flight density, but it’s what I have to work with.
I am also considering raising the antenna 30 feet (10m) above the current level to try to compensate for any loss of ADSB positions or aircraft.
It sounds like you are doing better than the nearby sites. Do you get dropouts when the aircraft are over water like the KLM flights in your last screenshots? Multipath can also occur from reflections off water. Not much you can do about that.
Yes. But I believe it is due to the distance: when this happens the distance would be greater than 200NM at high seas. I believe one of the reasons is the curvature of the earth.
My antenna is located 42 feet (13m) above the ground. In relation to sea level it would be 118 feet (36m). But as I said before, I intend to leave the elevation of the antenna above the ground at approximately 82 feet (25m) or 160 feet (49m) above sea level.
I also replaced the 5 meter RG58 cable sent by flighthaware with a 12m premium DLC213 cable to reduce attenuation losses. This cable would be the equivalent of an LMR400.
Hello. It seems that the problem is the signal level. This time, I tracked the same plane following the same route, leaving from the airport near here (Jericoacoara/10NM) and there were improvements regarding the loss of ADS-B positions.
