The Failed Promise of APRS

Is it just me, or is APRS more than a bit of a disappointment? Sure, it looks cool as a map display, but what can we really use it for?

This is the first in a series of posts that I hope are completely wrong. I am looking forward to emails explaining to me what an idiot I am and describing workarounds for all the issues I detail. Emails telling me—and demonstrating—that APRS really is as wonderful as I think it could/should be. Please prove to me that I am wrong.

I say at the beginning that no disrespect is intended to Bob, WB4APR, or any of the other people involved in making APRS work. And it does work—you can find my car (N5FDL-8) and home weather station (N5FDL-10) on APRS.FI right now.

APRS does work, it’s just not very useful to me an as emergency communicator. Why? Because the primary APRS network, on 144.390 MHz., is so congested that its hard to get packets through. Thus, when I am driving my vehicle with it’s dedicated 10-watt APRS transmitter, the network misses more packets than it receives.

That means that my vehicle can’t be tracked too very closely. And because of a “quirk” with the TNC software, when I stop it may take a long time for the network to figure out where I am, since my beacons go from once every couple of minutes to once every half-hour.

The software is only half-smart. It is able to “smart beacon,” based on my speed when I am moving (faster travel=shorter interval between packets) and will also beacon immediately when I turn a corner. When I stop my car, the beaconing immediately switches to a longer interval, suitable for fixed objects.

Here’s an email I sent earlier tonight to a friend, describing the issue:

Scenario: I am driving my car with the MicroTrak running. It is happily beaconing away—smart beaconing, actually—until I stop. At that point, the timer switches to the beaconing rate for a non-moving object, which might be every thirty minutes. That is great except…

The Problem: If everything has gone pretty well with network congestion, one of my recent packets was received and while the network won’t know my precise stopped location for 30 minutes after I stop, it has a pretty good idea where I am.

Or not, depended on when my last packet was received. I am running into a problem where the network misses lots of my packets, apparently due to congestion—even when I am beaconing quite frequently—so the position shown for me on APRS.FI or even picked up off RF might be 10 minutes old.

That means that for the next 30 minutes I will be 10 miles away (presuming 60 mph) from my true location. And if the fixed location packets (once every 30 min) are missed, it could be hours before my actual stopped location becomes known. Not at all suitable for emcomm applications.

The fix: I’d like to suggest that when the vehicle stops moving that the software wait five minutes, sends a packet, and perhaps sends a few more either over the next five minutes (1 min intervals?) or every five minutes (up to 30 min, then once every 30) so the network has a decent chance of finding me quickly.

i understand the new Kenwood APRS mobile rig also offers smart beaconing. It probably works about the same and suffers from the same issue(s) I’ve described. Except that with more RF output, it has a better chance than my MicroTrak of overcoming interference. And since the Kenwood has a receiver (the MicroTrak doesn’t), the Kenwood should avoid transmitting over other stations. The same beaconing rate on the Kenwood should have a much better chance of making it onto the APRS network than the MicroTrak would have.

The point of this posting:

• The APRS network is congested—too congested for a user to be able to predict coverage/throughput. Too congested to be a reliable emergency asset for vehicle/object tracking if a significant degree of precision is required.
• Even state-of-the-art APRS applications/software could do more to improve throughput, though a receiver would probably help the MicroTrak at least as much. But, not all APRS devices are going to have receivers.
• The 144.390 APRS network won’t cut it for most emegrency applications. At least not where I live.

Again, I’d like to think I am wrong, so drop me a line and convince me. I have more to say about APRS and will do so very soon.

Comments

[Kristopher Marciniak]

Easy fix for your problem if you have the ability to do profile switching (OT+, Tracker2, etc)
Create 2 profiles.
#1 Smart Beacon setup - vehicle is moving (may want to set the "slow" to 600 seconds).
#2 30 minute beacon - vehicle is stopped
Profile switching:
#1 When MPH < 2 Then switch to #2 + Transmit when switching to this profile.
#2 When MPH > 5 Then switch to #1

Stopping for a few intersections is going to add a few packets to the QRM.
Taking your stopped profile down to 30 min or even 60 min is going to remove from the added QRM. If your tracker can report the voltage of the vehicle, try this:
#1 When MPH < 2 AND Volts < 13.2 Then switch to #2

Now it will transmit as soon as you stop and shut your car off.
Or as soon as your alternator dies and you roll to a stop. ;)
- Kris
KI6IUC