max range 299nm

[djchiro]

Why is it that some stations all have a max range of 299nm and a few have something crazy like 350nm+ ?

If I look at my stats in graphs1090, I see repeated tracks with data above 299nm at night. These aren't just anomalies. Yet, the max range I get reported on rb24 is 299nm. It never goes above, ever. And some of the neighboring stations also have max range 299nm. How do some stations break through that 299nm "cap" that appears to be set? The metrics for the leaderboard do not seem to make any sense.

EDIT: I notice the stations reporting above 299nm are PGAxxxx... Is that one of the AirNav 1090 devices?

[AirNav Support]

None RadarBox devices (including windows sharer) are limited to 299nm to protect from fake positions being sent.

[djchiro]

None RadarBox devices (including windows sharer) are limited to 299nm to protect from fake positions being sent.

Are they limited or not? Your answer is unclear. It seems only PGANRBxxxx devices are reporting above 299nm. I know that my station regularly receives valid (multiple messages with positions) above 299nm daily. Yet my max range is 299nm.

[[email protected]]

It will depend on atmospheric conditions.  1.09GHz is mostly line of site, but there is atmospheric refraction and sometimes ducting that will usually extend the range.

There are area specific refraction tables for planning microwave links. The tables have a K factor, which the Earth's radius is increased by to get the expected range (a bigger Earth would have a more distant horizon).  Usually the range is extended, but sometimes the refraction will reduce the range, by refracting away from the earth. This is season, weather and area dependent. It can be a real problem for stable long distance microwave links.

The refraction occurs at the boundary between different layers of air.  Ducting is refraction within a layer, and is leaky in nature.   Ducting is common just above the ocean, where there is a layer where the air is more humid.  It has been used in tests of over the horizon microwave links, and in over the horizon radar. For radar, it is one of the reasons why ships mount their radar as high as possible. The radar needs to be above the ducting layer.

[Runway 31]

The way I read the post is that all feeds apart from Radarbox suplied receivers are limited to a maximum of 299 miles to protect against bad results being received

Alan

[djchiro]

OK but it still doesn't make sense. Then what receivers are able to report great than 299nm because I see some with the PGANRB prefix reporting above 299nm. Seems strange that some would be capped and others not. My receiver regularly tracks planes at greater than 299nm as I am located 325ft ASL and have clear LOS NE-E-SE which is all below me and out in the ocean. Yet it never reports that data in the RB24 leaderboard.

[Runway 31]

PGANRB***** receivers are Airnav supplied xrange receivers.  Its about data quality and an attempt to minimise erroneous data i would presume

The leader board is not all about range if you hover over the word score at the top of the column you will see the formula used - uptime^2 * (Avg range + (Max range /5)

I would presume your score would be higher is you had better range to your west.  The leaderboard is a bit of fun and not to be taken seriously although I know lots do

Alan

[djchiro]

Thanks for the explanation. I have about 90% coverage according to the data. My challenge to the west is the Appalachian mountains, so not much I can do about that. It still seems unfair to know that I would get >299nm reported only if I had an Airnav supplied receiver.