[aprssig] Weird Behavior on the APRS-IS

Stephen H. Smith wa8lmf2 at aol.com
Mon Feb 17 22:56:00 EST 2014

On 2/17/2014 10:22 PM, Steve Dimse wrote:

> the timestamps all appear to be in order at first glance.
> If you have object PACKETS that identical (same timestamps, positions, AND same senders) but with the 20 minute offset then please share the exact packets so I can look at findU's timestamps and see if there are any clues there.

That's what it is!   It's the SAME object from the  KJ4ERJ-15 source entering 
the APRS-IS at  fourth.aprs.net .    I jump through hoops trying to filter out 
other (usually massively erroneous) "ISS" objects by entry point, originator's 
callsign, etc.  [There's a station in the UK that keeps injecting bulletins 
announcing AOS and LOS of the space station without saying WHERE. He also keeps 
injecting an ISS object with a speed vector saying the ISS is traveling at 999 
MPH (and about a third of an orbit off).]

Unfortunately, I don't have any logs reflecting this incident and currently the 
two maps plotting this identical object, but received via two different IS 
servers are once again in sync.

I was really just wondering if anyone was aware of some sort of major 
disturbance, server problem, router outage, etc on the APRS-IS Sunday evening.

All this came up as I was reconfiguring my APRS server with several new virtual 
machines running on my Win7-64 host, so I was focusing more on getting multiple 
IP addresses and port numbers untangled.  The coincidence of the delayed object 
at first had me thinking I had something screwed up at my end.  It took me a 
while to realize it was an unrelated problem.   (Had about a 4 hour outage of 
my server last night for the reconfiguration.)

> [If I had a Windows app that could generate the ISS track locally from keps, and emulate an APRS-IS server on   localhost:portwhatever  I wouldn't bother with the Internet ISS feed at all.]
> There is an open source app on the AMSAT web site that I use (predict), it runs on Mac and Linux, but there are also Windows apps that I haven't looked through. It is in C so it could be made to run on Windows. Certainly none will directly emulate APRS IS, but if you can grab data from APRS IS you can grab data from a local program, predict can send data to a socket or produce results through a command line call. In my experience depending on objects sent via the APRS IS for satellite tracking is not going to give you reliable results, especially if you are just looking for objects called ISS. If KJ4ERJ-15 is producing reliable values and you are willing to depend upon it then you need to be sure whatever parsing you are doing ignores objects sent by all others, either within the parser or through APRS IS filtering.
> Steve K4HG
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