Should you use MIC-E compression in your APRS tracker

At first, the MIC-E compressed packets might seem to have advantage in reducing channel utilisation and improving the probability of successful packet transmission… but it comes at a cost.

The linux iGate daemon aprsd 2.2.5-15 has had a problem with corruption of MIC-E packets for more than ten years resulting in occasional gross errors in position reports processed by those nodes.

Here are some example packets, the pairs contain an uncorrupted packet and a corrupted copy via VK2ZEN-5.

  1. 2014-08-24 10:51:50 EST: VK2YCJ-9>S2U1Q2,VK2RTZ-1*,WIDE2-2,qAR,VK2ZEN-5:`OE p#!>/
    2014-08-24 10:51:50 EST: VK2YCJ-9>S2U1Q2,VK2RTZ-1*,WIDE2-2,qAR,VK2RTG-5:`OE<0x7f>p#!>/ [Rate limited (< 5 sec)]
  2. 2014-08-24 13:58:16 EST: VK2GKA-7>ST29Q3,WIDE1-1,qAR,VK2RM-3:`N:<0x1c>+5<0x7f>‘/>”?u}=
    2014-08-24 13:58:18 EST: VK2GKA-7>ST29Q3,VK2RTZ-1*,qAR,VK2ZEN-5:`N: +5 ‘/>”?u}=  [Rate limited (< 5 sec)]
  3. 2014-08-24 14:01:21 EST: VK2GKA-7>ST31W6,WIDE1-1,WIDE2-1,qAR,VK2OMD-3:`N6<0x1f>*s*’/>”@D}=
    2014-08-24 14:01:25 EST: VK2GKA-7>ST31W6,VK2RHR-1,WIDE1,VK2RTZ-1,WIDE2*,qAR,VK2ZEN-5:`N6 *s*’/>”@D}=  [Rate limited (< 5 sec)]
  4. 2014-08-24 14:23:38 EST: VK2GKA-7>ST29X5,WIDE1-1,WIDE2-1,qAR,VK2OMD-3:`N;G) <0x1e>‘/>”>U}=
    2014-08-24 14:23:41 EST: VK2GKA-7>ST29X5,WIDE1-1,VK2RAG-1,WIDE2*,qAR,VK2ZEN-5:`N;G)  ‘/>”>U}= 

Since it is apparent that aprsd has a significant problem and is not maintained at its Sourceforge site, it would be better if it were not used any more… but after 10 years that doesn’t look likely, corrupting infrastructure is a continuing ‘feature’ of APRS networks.




Screenshot - 24_08_2014 , 14_34_06

VK2ZEN-5 (mapped above) is an aprsd iGate that has a huge catchment. If you create posits anywhere from Bega to Port Macquarie and west to Dubbo, you are likely to have some packets iGated by VK2ZEN-5, and if they are MIC-E, some are likely to be corrupted.

If you operate in this area, give consideration to avoiding MIC-E format messages and MIC-E only trackers (eg Foxtrak, TinyTrack v1).

OH2KKU proposed a patch to fix the aprsd problem nine years ago: .


You can do something to avoid these corruptions… just don’t use MIC-E if you have the choice.

Some early low end trackers might not allow other than MIC-E, so your choice is to ditch them (ie upgrade) or be part of the problem.

If you can configure your tracker to not use MIC-E, you don’t feed packets into the network that aprsd may corrupt.