Rediscovering the Smartbeaconing™ Parameters

It’s been long since I had last used the TH-D72A to draw a track in, and I had since forgotten the meaning of all the Smartbeaconing™ parameters. It was time to try to rediscover them:

Smartbeaconing™ is a proprietary algorithm designed to save on resources when sending position updates in the Automatic Packet Reporting System (APRS). It was first conceived and developed by Tony Arnerich KD7TA and Steve Bragg KA9MVA in 1998 ( In essence it allows more frequent transmissions the fastest the movement and the changes in position.

It uses seven parameters:

  1. Slow Speed
    This is the moving speed below which no change in position is detected
  2. Slow Rate
    This is the interval for transmissions when moving below “Slow Speed”.
  3. Fast Speed
    This is the moving speed above which transmissions will occur at the “Fast Rate”.
  4. Fast Rate
    This is the interval for transmissions when moving above “Fast Speed”. )

In between the “slow” and “fast” speeds transmissions occur at intervals proportional to the actual speed.

In addition to this the “corners” need to be “pegged” to ensure that directional changes – even those taken at low speeds – trigger a position update. This is achieved by the remaining parameters:

  1. Minimum Turn Angle
    This is the minimum angle triggering a transmission.
  2. Minimum Turn Time
    This is the interval for transmissions when the direction is changed continuously. It has been recommended to be set close to the minimum interval allowed by the network: 60-120 secs. for VHF ( However, the use smaller values seems to be common practice.
  3. Turn Slope
    This parameter is explained differently by different sources and part of the confusion seems to be due to its name, since it is not a “slope”. Its actual units are degrees x distance / time, more precisely: degrees x speed units ( so that when divided by the current speed it yields a degree angle value that when added to the Minimum Turn Angle will produce the actual angle (proportional to the current speed) to trigger a transmission at that particular speed. The nature of this parameter can be easily appreciated directly from the algorithm ( In the Kenwood TH-D72A 1/10th value needs to be entered.

The TH-D72A has two menu items dealing with the settings for Smartbeaconing™: Item 3F “SmartBcon1” for Slow/High Speed, Slow Rate and Fast Rate and Item 3G “SmartBcon2” for Turn Angle, Turn Slope and Turn Angle.

My preference is to use distance units in Nautical Miles (nm) and speed units in Knots (Kts). This is not too much of a problem since the difference from Statutory Miles (m) and Miles per Hour (mph) is only a factor of 1.15 (i.e., ~1) and with Kilometers (km) and Kilometers per hour (kmh), a factor of 1.85 (i.e., ~2).

  • For car driving I decided to use the recommendation in APRS.NET (
    • Low / High Speed: 5 / 60 kts
    • Slow Rate: 30 min (1800 sec)
    • Fast Rate: 3 min (180 sec)
    • Turn Angle: 30 deg
    • Turn Slope: 25 (10 x deg x speed, hence = 250)
    • Turn Time: 15 sec

Here is the track of a recent road trip using these settings:

VA3PCJ-12 Jeep Track

  • For walking I found this recommendation by Adam KC2ANT in the APRS Yahoo group ( However the Salt Spring Island Amateur Radio Club ( suggests the use of a higher High Speed value. For corner pegging I used the same values as those for bicycling:
    • Low/High Speed: 2 / 10 Kts (2 is the lowest value allowed in the TH-D72A)
    • Slow Rate: 2 min (120 sec)
    • Fast Rate: 60 sec
    • Turn Angle: 30 deg
    • Turn Slope: 24 (10 deg x speed, hence = 240)
    • Turn Time: 30 sec
  • For sailing I was unable to find a complete definition of parametric values. However, the following are values that seem appropriate for a Com-Pac SunCat 17 with a hull speed of 4-5 kts. Unfortunately, I have been unable so far to test these settings on the water due to the lack of APRS repeaters readily accessible to the TH-D72A from Sassy’s sailing waters.

I welcome the input from others, particularly with regards to the Smartbeaconing™ sailing parameters.