'Rogue' planes out at the 250+ mark

Every few days or so my stats indicate I’ve picked up a few aircraft at the outer limits (250+ category). This would be interesting/exciting, except it’s in the opposite direction of the bulk of my long distance traffic. Any others see this? Any ideas?

FWIW, it’s a pretty simple setup. Home made Franklin collinear (14 guage wire, 138mm segments) zipped tied to a 1m plastic pole on top of my garage roof. No amp or filter, using 3m of cheap coax harvested from a cheap eBay ADS-B antenna into the SDR & raspberry Pi (in the rafters of the garage).

Sometimes they’re real, and the flight is just skimming the edge of your coverage area. For example, I sometimes get a few blips from flights between Fort MacMurray and Calgary, just enough to register that they are there. Occasionally and under the right conditions, those blips can go further than is ‘technically’ possible.

On the other hand, I’ve also seen some flights where I pickup the transponder but the position is 180 degrees off for the first few reports and then when the signal gets clearer the location gets interpreted properly and the plane moves a few hundred kms to the opposite side of the map.

It happens a lot less, once I turned down the gain and added filters, but it still happens

And then there are the the aircraft with bad transponders that seem to move across the country in the blink of an eye, only to jump back again a few minutes later.


You can also get airplane scatter.
en.wikipedia.org/wiki/Radio_pro … scattering
Hams in Aus use it to talk between Sydney and Melbourne(among others) on VHF and UHF.

Tropospheric Ducting is another possibility

There are a few aircraft that fly at FL510. These guys would have a much greater range than the STD FL400 that most passenger aircraft go up to.

There are times when I can see one to two dozen aicraft on the ground at JFK, LGA or EWR.
Sometimes it lasts for hours sometimes just a few minutes.
The signals are probably reflecting off something.

This generally means you have your max range set too low and receiver-relative position decoding is picking the wrong result; it fixes itself once you have enough data for global position decoding.