APRS Reference Information

Digital modes are increasingly used for emergency and public service communications, and Automatic Packet Reporting System (APRS) is no exception. Most radios and trackers come with reasonably sane defaults for general use, but events may require special settings.

General Use Settings

Unless otherwise noted, all APRS stations in Eastern Iowa should run APRS 5-10 W in a metro area, and 10-20 W in rural areas. There is no need to run 50+ W, and doing so can actually interfere with distant APRS stations.

Mobile vehicles (anything that can maintain more than 5 mph for an extended period)

  • Set the beaconing algorithm to SmartBeaconing [R] or Genius Beaconing [R], if either is available on your rig. These algorithms calculate optimal beacon times, which a) makes the actual track more useful, and b) reduces congestion on the APRS frequency.
    • Special note: the default settings for these algorithms seem to be fine for all vehicles, but you might consider reducing the top speed on SmartBeaconing [R] for bikes.
  • If a ‘smart’ algorithm is not available, set the beacon to ‘auto’ with a beacon time of not less than five minutes. If your rig supports proportional pathing and decay algorithms, leave them on. (No need to change their settings otherwise…the defaults are optimal.)
  • Set your path to WIDE1-1,WIDE2-1. Make sure they are in that order, and do not use any other path.
  • Do NOT run a mobile digipeater. This is unnecessary in this area, and causes problems.

Other Mobiles (walkers, runners, canine units)

As per mobile vehicles, with the following exception:

  • Do NOT use a smart algorithm. Set to ‘auto’ with rate at five minutes. At walking speeds, the smart algorithms will ping only every 30 minutes or so, which is too long to be useful.

Fixed Stations

  • Fixed stations should set path to WIDE2-1 at a minimum beacon time of 30 minutes.
  • This also applies to almost all objects generated. There are situations where a shorter beacon time is necessary. If you are not sure if this applies to your station…it probably doesn’t. As always, questions are welcome. Just ask a local APRS guru!

Special Event Settings

Event units tend to be a) chase vehicles, b) resource trackers (in sag wagons and such), or c) fixed stations.

Chase Vehicles

  • Set ping rate to ‘auto’ and time to two minutes unless otherwise instructed by net control. Smart algorithms will actually do a good job of marking the path, but they don’t give NCS a good feel for where anyone is on a straight leg. Ping rate needs to be regular and short to allow NCS and event staff to see the chase vehicle’s location at any moment.
  • Turn Proportional Pathing and Decay Algorithm OFF! Pathing will cause the path for the packet to change with every beacon…WIDE2-1, WIDE1-1, then direct (no digipeating). This can cause NCS to not receive all packets, and thus lose track of your location. Decay algorithms will lengthen the beacon interval if position is changing slowly. Good for normal use, but bad for events. These are both ON by default in every rig we’ve ever used, so make a point of turning them off.

Resource Trackers

Use the chase vehicle settings unless instructed otherwise by NCS.

Fixed Stations

Generally speaking, NCS will arrange for a central station to beacon ‘objects’ for fixed stations rather than having those stations beacon for themselves. This gives NCS better control of the frequency and the objects. NCS will inform you if you need to set your own beacon, which should be ‘auto’ with about a 30-minute beacon rate. Previous admonishments about pathing and decay will apply.


Smart Algorithms

‘Smart’ algorithms calculate beacon rates according to conditions, changing the rates based on speed, location, direction, etc. There are many ways to do this, but two algorithms are prevalent: SmartBeaconing [R] and Genius Beaconing [R].

SmartBeaconing is used in Kenwood rigs. The algorithm is open — search the web and you’ll find it. Please note that it is trademarked and copyrighted to prevent commercial mis-use. You likely need permission to include it in your products. The algorithm has two parts relating to speed and direction. The speed algorithm decreases the time between beacons as speed increases. The direction algorithm is a bit more complex, but forces a beacon when your direction changes more than an amount determined by your speed. It works quite well for moving vehicles, but seems lacking when vehicles are not moving (if you stop for a train, you won’t get the final position beacon for 30 minutes).

Genius Beaconing is used in APRSIS32, a fine and full-featured tracking program. Where SmartBeaconing uses speed and direction, Genius Beaconing uses position. It calculates where the world thinks you are based on the data in your last packet, then compares it to your current position. When the error gets large enough, it forces a new beacon. This avoids the “last position” issue that SmartBeaconing has, but it also doesn’t beacon right on turns as SmartBeaconing does. (Seems like someone could combine these algorithms somehow….)

Digipeaters and Gateways

Here is the preferred policy for Linn County:

  • Digipeater BEACONS should be set to a WIDE2-1 at a 30-minute interval. This is the beacon path only! See below for paths for which packets to digipeat.
  • Wide-area digipeaters should have their path set respond to WIDE1-x and WIDE2-x packets. Please note that we do NOT need any more wide-area digipeaters at this time! The greater Linn County area is covered nicely by the digis at Rockwell Collins (N0CXX) and the massive digi in Morse (K0HAM, top of a 300-foot tower).
  • Fill-in digipeaters are sometimes needed to fill the inevitable coverage gaps in the wide-area digis. Paths for fill-in stations should be WIDE1 (that is, they will digipeat ONLY WIDE1-1 packets), and should digipeat the packet as WIDE2-1 so the wide-area units will hear them. No other path settings are appropriate for fill-in digis.
  • NO MOBILE DIGIS, please.
  • The more gateways, the merrier! Gateways forward the packets through the internet to the APRS-IS backbone for access from the web. It is NOT necessary for a gateway to also be a digipeater, but if it is, please adhere to the previous guidelines. We want to have at least two gateways active at any given time, and it’s even better if their internet connections are with different providers (in case one is out). Multiple gateways do no harm to the system, as they are not cluttering the RF channel.
  • We use the national APRS standard frequency of 144.390 MHz, with large-scale events on the alternate 144.990 to prevent clutter. Other frequencies can be used (within the limits of Part 97), but to date, there has been no need.


MIC-E is a bit of a carry-over from commercial vehicle tracking systems. It can be useful, but some MIC-E settings will cause APRS programs and trackers to react in special (and distracting) ways.

In particular, setting MIC-E to EMERGENCY, PRIORITY, or SPECIAL will cause programs such as APRSIS32 to pop up an alert window. The same is true for some mobile rigs. Therefore, our protocol for MIC-E is:

  • Set it to Off Duty (the default/’null’ setting) for all normal operations.
  • Set it to EMERGENCY if and ONLY if there is an actual emergency and you are not otherwise able to make contact with someone to cover it. “Emergency” here is defined as a clear threat to life or limb.
Reviewed 5 Oct 2013