Sporadic ground reception


#1

I’m curious what may be the cause of very sporadic ground reception. I’m about 10.2 nm from our local international airport and it’s non line of sight from my position. I am running two sites for testing and tuning purposes and I recently bumped up from PiAware 3.0.5 to 3.1.0 on both sites (still using mutability). I know there have been some recent tweaks on how PA processes ground messages looking through the repository, but I can’t explain what I’m seeing: Here is a 6-hour duration collectd graph for reference from one of my sites:

http://puush.hopto.me/Y87K

As you can see there are sporadic increases in both positions and plane-count. Looking at it in real-time as it’s happening, it’s definitely attributed to ground sightings as all of a sudden for the 5-15 minute duration I can see the map light up like a Christmas tree when zoomed into our main airport with planes on the ground.

I guess my question that comes to mind is why is it for short durations only? I haven’t seen correlation in atmospheric conditions/weather or other major changes during this time (obviously the naked eye and radar/doppler cant tell the whole story when it comes to RF). Are there some planes outfitted as relays that are pissing signal on me when in range, or is this some strange anomaly where signal randomly echoes towards my position for 5-15 minutes at a time? I suppose the algorithm is still being refined and I am viewing this as a step in the right direction over prior versions, but felt the need to ask since I’m s̶o̶r̶t̶ ̶o̶f̶ totally stumped over what I’m seeing.


#2

Probably TIS-B?


#3

That would be the assumption, but am only ADS-B-In, also not listening to UAT as a supplement - yet receiving intermittently still? Have seen some conflict whether or not non ADS-B-out equipment would/should receive TIS-B in the first place, but not comprehending the hierarchy. Perhaps some aircraft are transmitting more promiscuously?

Since I’m obviously still trying to staple jello to a wall, can explain a bit?


#4

Check out how TIS-B works
en.wikipedia.org/wiki/Traffic_i … _broadcast
aopa.org/news-and-media/all … s-to-tis-b
faa.gov/nextgen/library/med … t_ADSB.pdf
faa.gov/nextgen/update/gene … tion/adsb/

There is also ADS-R, but it is more likely to be TIS-B.

I get this daily as I am close to KLGA, KJFK and KEWR airports.


#5

TIS-B happens on the existing frequencies so anything with ADS-B in can hear it.
The ADS-B out part of the puzzle is that TIS-B is only transmitted when there is an ADS-B out transponder nearby that advertises it has ADS-B in.
Once that is triggered anyone with ADS-B in can hear the results.


#6

OK so from what I’ve been reading and what I think you are saying (apologies for being dense): Given the amount of traffic in my general area, it would appear that few aircraft are currently equipped with ADSB-out and when one comes into range, I’m receiving the (triggered) TIS-B - hence the spikes. Oddly enough, have never seen prior to moving to v3.1.0. That would explain the seemingly random spikes if I’m reading this correctly. Thanks kindly for the replies.


#7

I found this thread when I was looking up why sometimes I get a large number of ground entries from LAX. Zooming in it’s neat to see where all the planes are at the terminal.


#8

I believe this is the reason that my ADS-B and MLAT “Positions Reported” statistics are so wildly exaggerated.

Most of the positions I’m credited for, are non-existent, “ghost” returns.

JMHO


#9

A nifty bit of parking at LAX :astonished: :open_mouth: :smiley:

Captured by Jeroen Stroes. © Jeroen Stroes