Degrading performance

[Jim Percy]

Any thoughts on how to efficiently determine which of my components is failing? I started with a Micro-Trak 300 and cheap whip antenna, with the unit taped to the top longeron in the baggage compartment. Here's what I got on my first flight (a formation practice):

http://aprs.fi/?call=N373JP&dt=1221868800&mt=m&z=11&timerange=86400

Slowly, over time, the performance seemed to degrade. I wasn't necessarily aware of it because I was trying some tweaks and such. Somewhere along the way I added the 8 watt micro amp with limited improvement (still not back to the original quality), and yesterday tested my wingtip installation complete with J-pole antenna only to get this:

http://aprs.fi/?call=N373JP&mt=m&z=11&timerange=86400

Clearly something isn't performing up to snuff. I'm going to give Pete the benefit of the doubt and guess it's NOT his J-pole, so that leaves the GPS or the transmitter (I copied the transmitter configuration from Pete too, so I'm gonna guess that's also OK). Any suggestions on how to troubleshoot before I start buying and swapping in new parts?

Thanks!

 

[Sam Buchanan]

Any thoughts on how to efficiently determine which of my components is failing? I started with a Micro-Trak 300 and cheap whip antenna, with the unit taped to the top longeron in the baggage compartment. Here's what I got on my first flight (a formation practice):

http://aprs.fi/?call=N373JP&dt=1221868800&mt=m&z=11&timerange=86400

Slowly, over time, the performance seemed to degrade. I wasn't necessarily aware of it because I was trying some tweaks and such. Somewhere along the way I added the 8 watt micro amp with limited improvement (still not back to the original quality), and yesterday tested my wingtip installation complete with J-pole antenna only to get this:

http://aprs.fi/?call=N373JP&mt=m&z=11&timerange=86400

Clearly something isn't performing up to snuff. I'm going to give Pete the benefit of the doubt and guess it's NOT his J-pole, so that leaves the GPS or the transmitter (I copied the transmitter configuration from Pete too, so I'm gonna guess that's also OK). Any suggestions on how to troubleshoot before I start buying and swapping in new parts?

Thanks!

Jim,

I suspect your degraded tracking is due to problems with a misconfigured digipeater. Take a look at your latest "raw packets" data:

http://aprs.fi/?c=raw&call=N373JP

Most of the errors are associated with the KB6TWC-3 digi. I suspect that station is buffering packets which creates collisions on the aprs.fi server. When these collisions occur, the packet gets thrown out and a gap appears in your track. Digis that aren't set up correctly are not uncommon but usually don't degrade the overall performance of APRS a significant amount.

Looks like your tracker is working fine. Try a couple of flights to a different area of your world to make sure you are dealing with a local problem. If you check "raw packets" and see a lot of red, you are most likely dealing with problems beyond your control.

 

[Jim Percy]

Thanks Sam. I guess it has been a while since I've ventured a significant distance from the nest, maybe I should try that.

As for all the red, is there really nothing to be done? I understand about we aviation users treading lightly on "their" system and all, but can/should such things be be brought to someone's attention? Or should I just keep my mouth (or keyboard, as it were) shut and let the powers that be figure it out for themselves? Granted, leaving a trail of dots in my own backyard isn't really that important, but still...

 

[Sam Buchanan]

Thanks Sam. I guess it has been a while since I've ventured a significant distance from the nest, maybe I should try that.

As for all the red, is there really nothing to be done? I understand about we aviation users treading lightly on "their" system and all, but can/should such things be be brought to someone's attention? Or should I just keep my mouth (or keyboard, as it were) shut and let the powers that be figure it out for themselves? Granted, leaving a trail of dots in my own backyard isn't really that important, but still...

We need to get over the idea that APRS is "their" system. As the holder of a Technician license, we are legitimate users of the Amateur Radio Service on any frequency or service designated for Technician license operators.

As to what can be done about misconfigured APRS stations, it would probably be best to be an active member of a local ham user group before making much of a fuss. Don't forget that some digi operators are "newbies" as well and may be struggling with software configs just as several of us have experienced in the course of setting up iGates. But once we become a known participant in a local ham club, I think it would be appropriate to poke around and inquire if anyone is acquainted with the station operator.

There is a lot about packet errors I still don't understand. In my area, some flights have several errors, and other flights at a different time are practically error-free. Fortunately my area is blessed with several iGates so my beacons usually consistently make it to the network. A fair amount of power and efficient antenna certainly helps.

APRS is a fantastic application for aviation but it isn't perfect. We are after all talking about amateur radio.

Having said all that, be sure you do not have any issues with antenna connections on your tracker. That is about all that will degrade tracker performance given no catastrophic failures have occurred with your rig. I can also tell you I had problems with an external amp on a MT-300 but others seem to have gotten that combination to work well. It looks like your tracker is shooting out beacons just fine but I don't know how to explain the five minute gap in your beacons early in your flight.

 

[petehowell]

Power Adjustment?

Jim,

I agree with Sam, it looks like the beacons are going out just fine. One thing to try is to actually turn down power on the micro-amp just a bit. I had one set too high and it was not sending a clear signal. Backing the power down, by adjusting the potentiometer, seemed to help quite a bit.

If you do think it might be the antenna, we can get you another one to try very easily. Just let me know.

 

[Jim Percy]

Thanks again guys. I took everything back out of the wingtip so I can more easily troubleshoot. I ran a new serial wire out from my panel mount GPS so I can try that, and I can now easily adjust the amplifier pot and try changing antennas too. I really don't think the j-pole is to blame Pete, because things seemed to be worsening before that. Thanks for your offer but for now I'll work with what I have.

My comment about "their" system was a little tongue in cheek I suppose, but in some sense I kind of prefer to be a periferal user. I suppose it wouldn't kill me to move a little closer to the ham crowd, would probably be the best way to figure this out. Someone with good test equipment (and the knowledge of how to use it!) could probably pinpoint the problem pretty quickly...

 

[Sam Buchanan]

My comment about "their" system was a little tongue in cheek I suppose, but in some sense I kind of prefer to be a periferal user. I suppose it wouldn't kill me to move a little closer to the ham crowd, would probably be the best way to figure this out. Someone with good test equipment (and the knowledge of how to use it!) could probably pinpoint the problem pretty quickly...

Jim, don't expect very many hams to have a working knowledge of APRS. It appears to be a very narrow niche of ham radio. One of the guys administering the exams when I tested asked me what I was interested in doing with the license, and when I mentioned APRS he didn't have a clue what I was talking about.

There is a "What to do with APRS" thread on the QRZ forum and most of the ham responders stated they thought APRS was a worthless service.

Us "newbies" know better, however, and I sure am glad we have APRS!

 

[Joe]

Someone with good test equipment (and the knowledge of how to use it!) could probably pinpoint the problem pretty quickly...

You're right, Jim. And if you'll fly into Independence Airpark, OR (7S5) I'll take a look at it on my service monitor

But there are a few "easy" things you can do to help troubleshoot. Now, I'm not trying to start any flame wars but what follows is MHO. I have a lot of experience in the RF end of things and have had excellent success with my APRS tracking for a number of years (unless I bump a switch and accidentally turn it off. I hate it when that happens

1. Turn off MIC-E and transmit plain text. Yes, I know it saves a few bytes but tell me which packet is easier to troubleshoot with respect to your position, altitude, and heading at the time of spotty coverage or some other anomaly .

`|1TlS#'/"4t} (contrived example; doesn't match plain text below)
or
!4451.89N/12311.53Wk232/011/A=000167/
(BTW, this is lat, long, symbol 'k' (plane), 232 degrees, 11 MPH, 167 ft)

Incidentally, the "few bytes" saved is largely overshadowed by the packet's header and comments fields. You can do the arithmetic: approx 24 bytes at 120 characters per second saves 0.2 sec once a minute or so.

2. Lose the WIDE1-1 in your PATH. It just doesn't net you any improvement these days (except under some rare circumstances) but can increase the possibility of a rogue Igate hearing you. Remember, you only need to be heard by one Igate and if it takes a digi to hit an Igate, that's OK, but if multiple Igates hear you, it increases your exposure to the "delayed packet" issue. I've been running WIDE2-1 exclusively with no noticeable degrading.

Incidentally, the APRS-IS network employs a 30-second "dupe filter" to discard multiply-Igated packets. Duplicate outside that window are not caught (at the APRS-IS level) and wreak havoc with position reports.

3. Due to the nature of RF, lots of antennas "work" under ideal conditions and give the appearance of being "good". Borrow or otherwise temporarily try another antenna -- even your 22-inch bent whip com antenna. Don't worry about the SWR, especially for test; it's not the most important antenna parameter. I remain suspicious of wingtip antennas, not because they're in the wingtip but because they're mostly horizontally polarized and the path loss due to cross polarization can be enormous.

Sam first mentioned the "buffered packet" problem, and I agree that it can be severe. Sometimes packets are delayed for days! I happened to be watching N929EH's current flight and was dismayed to see his most recent track (and even his current position) are totally obfuscated due to rogue Igates and the filtering algorithm of aprs.fi. See the raw data at http://aprs.fi/?c=raw&call=N929EH&limit=1000. (I put a copy of it at http://www.mail2600.com/N929EH.htm in case it has already scrolled off aprs.fi).

Perhaps this a subject for another time but the problem occurs when packets are received but not immediately Igated due to Igate software issues. When they eventually are Igated, the timestamp causes them to be displayed out of sequence with proper packets. Generally, restarting their Igate software does the trick. I've found most Igate owners are concerned and cooperative when tactfully notified.

73,
Joe, K7JD

 

[Jim Percy]

Thanks for the information Joe. I think I'll pass on your kind offer to test my system, at least for now...

I plan to try most if not all of the suggestions posted, and I'll post my results. It may take me a little while, things are busy for me the next few weeks. Turning off MIC-E and getting rid of WIDE1-1 are certainly easy enough for a start.

Thanks again guys!

 

[VHS]

Turning off MIC-E is useful for debugging your data, but will cause your throughput to drop significantly.

Allen
VHS
AF60F

 

[Sam Buchanan]

new tracker configuration

1. Turn off MIC-E and transmit plain text. Yes, I know it saves a few bytes but tell me which packet is easier to troubleshoot with respect to your position, altitude, and heading at the time of spotty coverage or some other anomaly .

`|1TlS#'/"4t} (contrived example; doesn't match plain text below)
or
!4451.89N/12311.53Wk232/011/A=000167/
(BTW, this is lat, long, symbol 'k' (plane), 232 degrees, 11 MPH, 167 ft)

Incidentally, the "few bytes" saved is largely overshadowed by the packet's header and comments fields. You can do the arithmetic: approx 24 bytes at 120 characters per second saves 0.2 sec once a minute or so.


Joe, K7JD

Turning off MIC-E is useful for debugging your data, but will cause your throughput to drop significantly.

Allen
VHS
AF60F

A couple of flights ago I turned off MIC-E and added my ham call-sign to every packet. So far the performance of the new config has been splendid with few errors. It is kinda neat seeing the location, altitude and speed in the raw packets.