FlightAware Discussions

Yagi antenne for long distance ADS-B?

I found a Polish feeder with very exceptional long distance stats but only for one narrow direction, the only explanation I can find is that he/she is using a 1090MHz yagi as sold by Jetvision:

No MLAT, that’s just someone aggregating messages from 2 feeders.

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It’s a planeplotter feed, so could easily be that. Also might be that the position is set incorrectly displacing all the ranges/bearings.

I did that as an experiment on the FR24, to test my theory that a lot of users cheat that way (emulating distance by setting the wrong location for their radar).
Pushed my stats really high too, because FR24 doesn’t care to show the MLAT. Reverted since then.

The “Polish” guy is probably also cheating in another way too.
He has 228000 positions on the blue mark (that I think is his real location), and then drops to less than 500 on the further away sectors. Shows 4190 flights when no-one around him has more than 1500…

I tried building a 1090 MHz Yagi with the idea of optimization the NE direction where there are, or should be, lots of aircraft above the horizon that my system is not detecting.
The results were mixed.

First, it is hard to build a good Yagi at 1GHz. I controlled all dimensions to within 0.01” of the design figures. Centering the elements onto the conductive boom to required accuracy is especially tricky. Fabrication of the folded dipole driven element is harder than cutting the parasitic element lengths precisely. Tuning for VSWR requires adjustment of multiple variables. Eventually I rebuilt the antenna entirely with a non-conductive boom. That reduced the number of tuning variables.

Second, even when the Yagi is optimized and the gain is perhaps +12 dBi in the main beam the side-lobes are receiving lots of local traffic. I did see some preferential results in the main beam as seen by the FlightAware range-azimuth bin counts. But I did not see the results I wanted in improved distant traffic in the main beam.

I think (have not tried) that only an active side lobe suppression system will beam-sharpen the results significantly. That’s a different topic.