First experiments with APRS

After success with Winlink described in a previous post, I wanted to try out APRS (Automatic Packet Reporting System). The components are exactly the same as with my Winlink experiment:

  • Laptop running Dire Wolf
  • SignaLink USB
  • Yaesu FT-70D VHF/UHF radio

Then it was just a matter of configuring the direwolf.conf with this line:

PBEACON delay=01:00 every=15 symbol="/-" lat=59^56.60N long=010^46.60E power=5 alt=60 gain=2.15 comment="APRS test" via=WIDE1-1

For Norway, the frequency is 144,800 MHz. This can be found in the band plans for Norway that NRRL maintains.

With this setup, my position will be transmitted every 15 minutes, and I can also receive messages. The part where it says via=WIDE1-1 means that the APRS packet can be forwarded by a maximum of one digipeater.

For APRS one should use what is called Secondary Station Identifier or SSID. This is a convention to make it easier to see what type of APRS application is in use. The SSID for my stationary APRS would then be LB2KK-0 or just LB2KK. If I had a weather station, it would be LB2KK-13 and so on. See APRS SSID Recommendations for the full list.

Use cases for APRS

Most examples that I found are about position tracking. This can be used for cars, boats, humans, and your QTH. Another common example is weather stations that send temperature, wind speed, etc. These are examples of one-way communication. It is possible to use it as a two-way communication system as well. I can for example broadcast the frequency I’m listening to when mobile. LA4A uses APRS to broadcast information about their repeaters which can be used to automatically configure the frequency offset, TSQL, TONE, etc. One such repeater is LA5AR which has 145.700MHz t123 -0600kHz NETSu8PM in the APRS object. It even contains the time for the local net: Sundays at 8 PM.

Links

General APRS information:

Some information about the use of APRS in Norway: