APRS traffic study – VK2OMD-3 08/02/2015

APRS traffic study – VK2OMD-3 11/10/2014 reported a study of APRS traffic.

This article is an update after configuration changes at VK2RHR-1 to make it a ‘fill-in digi’, it repeats packets addressed to WIDE1 only.

The study of APRS traffic was conducted by analysing the log of VK2OMD-3, a VHF APRS ‘fill-in’ digi and iGate.

The capture period was during from 0700-1700 local time on Sunday 08/02/2015.

Note that any study that counts decoded packets underestimates channel utilisation as packets with errors as a result of interference, collisions, propagation are discarded in the decoding process.

Google Maps APRS - Mozilla Firefox firefox 14/10/2014 , 09:29:17

Above is the geographic topology. VK2OMD-3 is located about 100km SW of Sydney and does not directly hear Sydney or coastal traffic.

Two prominent local digpeaters (VK2AMW-1 and VK2RHR-1) each about 20km distant are heard very well, and one prominent distant digi (VK1RGI-1) at about 190km is frequently heard well, but subject to varying propagation conditions.

The changes in VK2RHR-1 configuration have reduced repeats of packets that mostly are also repeated into the area by VK2AMW. The average traffic level was about 55% that of the previous study, and notable factors are:

  • no traffic observed from VK2RAO-1;
  • reduced traffic from VK2RTZ-1 (it may be a W1 digi now);
  • higher traffic from VK2RAG-1;
  • reduced air time of out of area traffic as VK2RHR was not repeating it.

Nevertheless, distant digipeaters accounted for 29% of the total traffic heard at VK2OMD-3. Note that the impact of this traffic is double to the VK2RHR-1 and VK2AMW-1 repeater inputs.

Screenshot - 09_02_2015 , 01_10_59

The flow diagram above charts the major traffic flow during the ten hour sample period, 2653 packets in all, and average rate of 265/hr. For short periods of time, traffic intensity might easily be double that rate, and the intensity at the two local digis might approach double that again (the above counts are packets received at VK2OMD-3 and do not include those received at the local digis but not heard at VK2OMD-3).

Off air observations are that mobiles travelling through the area are achieving higher posit rates to APRS-IS, probably mainly due to reduced channel congestion.

The Goulburn and Southern Highlands Radio Club deserve credit for thinking creatively about improving the service, something that is quite unusual in the APRS community it seems


Service can be improved by optimising repeater strategies.


Diagram in PDF: VHF APRS traffic study VK2OMD-3 08_02_2015