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[Rate limited (< 5 sec)]

petehowell

Well Known Member
Do any of the more experienced APRS'ers know what this means [Rate limited (< 5 sec)]? When I get packets rejected, it is most often for this reason. Is this the APRS system comparing packets and saying something is wrong, or is it my unit sending bad data?

It happens during tight turning/goofing off. I'm wondering if a smartbeacon parameter change might help.
 
Rate Limited

Pete, it appears "rate limited" is a term aprs.fi uses to describe packets that are discarded when the position is updated too frequently. And apparently it's set at 5 seconds or less.

73,
Joe, K7JD
 
Do any of the more experienced APRS'ers know what this means [Rate limited (< 5 sec)]? When I get packets rejected, it is most often for this reason. Is this the APRS system comparing packets and saying something is wrong, or is it my unit sending bad data?

It happens during tight turning/goofing off. I'm wondering if a smartbeacon parameter change might help.


Pete, this blog entry from the guy who owns aprs.fi is pretty interesting:

http://oh7lzb.blogspot.com/2008/03/on-duplicate-and-delayed-packets.html
 
Sam, the blog cleared a lot of questions. I was wondering how can I traveled more than 500 kmph in my RV. Now I see. However I still see some zig-zag paths. It seems that there is not much I can do about.
 
Thanks Sam!

The blog answered why - I'm now wondering if I just have to abandon tight tracking during steep turns. I looked at the smartbeaconing parameters but don't see a way to eliminate the rejected packets.

Joe and Sam - is 5 sec limitation a rule of APRS.fi or is that a general rule for APRS?
 
The blog answered why - I'm now wondering if I just have to abandon tight tracking during steep turns. I looked at the smartbeaconing parameters but don't see a way to eliminate the rejected packets.

Joe and Sam - is 5 sec limitation a rule of APRS.fi or is that a general rule for APRS?

Pete, as I understand the system the limitation is just on aprs.fi. It is the owner's method of eliminating junk packets in his proprietary parsing software.

One thing you might try is to increase the number of degrees the aircraft has to yaw before Smartbeaconing kicks in. I think we are using 25, maybe you could try 35. I still don't understand how "slope" effects Smartbeaconing, but messing with that setting might have good results. All this would mean the arc drawn in a turn won't be as smooth but there should be more time between beacons which might not trigger the 5 sec error.

I suspect we can expect to see some errors in spite of our best efforts to tweak our tracker config. If there are delays in the internet feed to the APRS portals, or somebody's iGate is buffering packets for some reason, and consequently packets are perceived by the server as invalid, there is nothing we can do about those errors.

But......even with a few dropped packets APRS is still an amazing service and one that serves our purpose well. In the real world having perfect tracking in tight turns isn't a concern, more of an interesting exercise in system refinement. If you spin into Mother Earth while doing tight turns over your girlfri...uh, flying buddy's house, the last beacon from your tracker will give us a good place to start looking. ;)
 
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Agreed Sam

APRS is great stuff - I am in the weeds tweaking this thing now. No complaints.
 
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APRS is great stuff - I am is the weeds tweaking this thing now. No complaints.

Pete, you are a bad influence! So I ran out and got my ham licence now and I'm tracking. My first flight had some bad coverage, so I modified my installation and tweeked some parameters.

Here's my flight today.

http://aprs.fi/?call=VA7VRL&mt=m&z=11&timerange=3600

FYI I'm using a MicroTrak 300 mounted inside the canopy on the seat back brace (right between pilot and copilot's ears). Low power, so this should be ok. Added a counterpoise today and the tracking seems fine except below 500' (probably due to the low power).

I have two modes: normal WIDE2-1 @ 60 secs and WIDE1-1, WIDE2-2 @ 30 secs. The second mode does not seem to be any more reliable than the first, and a lot of packets are discarded. I added it as an 'emergency' mode that I can switch to for additional pings, if required.

Very cool stuff. I added the aprs.fi link to my flightplan master, but the FSS folks said "we've not been trained on this stuff". I told them that if they had to find me, they would figure it out.

Vern
 
Good Show Vern!

Welcome to the fun. It is a neat gizmo and a nice backup safety device.

Tracking below 500' will be tough unless there is a digi close by, but most flying is above that alt anyway.

Let us know if you have any questions.
 
Welcome to the fun. It is a neat gizmo and a nice backup safety device.

Tracking below 500' will be tough unless there is a digi close by, but most flying is above that alt anyway.

Let us know if you have any questions.

Thanks, I may. I'm going to try a few long xc's with the setup in the cockpit. I also have a 6W 2 meter HT that I could use if that doesn't work. It's also my backup NAV/COM (pretty cool NAV/COM/APRS all in one HT). I'd have to come up with a multiband wingtip antenna. Now there's a design challenge:

One antenna for NAV band, COM band and 2M. Possible, I think. One issue may be the polarization differences, but that may be managable.

Vern
 
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