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What is APRS and why is it important?

APRS, or Automatic Packet Reporting System is an amateur radio system that sends locations, information and communications using digital communications. Some of its uses include Emergency Communications organization, tracking hams in the field during disasters or serving the population and agencies during marathons or bike races. It is also heavily used in weather spotting and storm tracking, balloon launches, as well as direct messaging. It is a still very popular niche of amateur radio that has major benefits in emergency communications as well as general information passing. It was invented in the 1980's by an amateur operator named Bob Bruninga, WB4APR (SK) and is still in heavy use to this day! The following information is what I've done on APRS, although it changes constantly! :)


DVLDEN is a full APRS digipeater and iGate located at my house. We're up on a mountain so helps with traffic gating from Devils Den and stuff to the southwest of Fayetteville Proper.

Equipment includes a HP desktop computer that runs Direwolf as a stand alone TNC and interface. The radio is a 25 watt CDM750 that is interfaced with a Repeater Builder USB RIM Lite.

I modified a Dell server power supply to provide 12VDC to the Motorola Radio from inside.

Here are some plans for using these power supplies.

I try to leave this run 24/7 for users to iGate/Digipeat at any time. 

ham van vara.jpg

APRS Equipment

Most of this stuff is inexpensive but works. The CDM750 is a stout radio and with minimal work makes a great APRS transreceiver as it works well within the 2M band. Dell power supplies are cheap and can be had much cheaper than comparative power supplies. The modification gives you fan adjustments, up to 60 amps draw and runs on AC. Likewise, the RIM-Maxtrac USB Sound Card is literally plug and play and has adjustments for audio for perfect clarity.

Get started with APRS!

1 / Get an APRS Passcode

You will need a Passcode before your station shows up on APRS sites like or findu. GO HERE .

2 / Get the equipment!

You will need a VHF radio that can operate at 144.390, a soundcard interface and a computer. There are multiple ways to do this. We review here what I've done and we can go from there!

3 / Take time on learning what APRS is, how to use it and where!

It would take forever to explain the details. I will add links to things to help you along and show what I've done so maybe you can copy! The digi I built helps cover the NWA and River valley to the south and is favored for I-49 and areas around Devil's Den State Park.


I used the Windows-based Direwolf so I could have some backward compatibility for VARA-FM in the case of a computer loss. Direwolf runs well on Windows with a little bit of effort. Although Direwolf is compatible with GUI clients like YAAC, APRSISCE/32 and so on, it can be setup to run and report on its own without an interface. For unattended operation, I decided that is the best way as it is less to go wrong. Direwolf does all the digipeating and gating on its own. Here are some tidbits...

  • Direwolf download for Windows is specific. The newest builds have CM108/PTT for transmit built in now. Download the file and extract to a place you can remember. Desktop, user folder, doesn't matter. Just remember where it is.

  • When you open the folder, there are a bunch of files in there, as well as a folder of how-to's and instructions in .pdf. Take time to review them. The user guide for Direwolf is written well and should help with most issues.

  • The two files you'll REALLY need to work with are the direwolf.conf file as well as the Direwolf application direwolf.exe. Direwolf doesn't "install" like a typical program as there is no installer. It runs right out of the folder, so make sure all the other applications stay in the same folder with it. 

  • You will need to edit the direwolf.conf file to get the program to work. In Windows, you can open this (it will ask the first time ha ha) with Notepad, as it is a simple text file. There is a lot of information online how to set this up for Linux, however, since we're using Windows, biggest thing is to have your radio interface plugged in and ready to go when you first start Direwolf.exe so it knows what to use for a sound card in Windows. You may need to go back to the config file to make changes. If you're using a RIM-Maxtrac interface, it will show up as something like USB PNP SOUND DEVICE. If you're using a Signalink, it will show up as USB AUDIO CODEC. Use this interface for both receive and transmit, depending on which you have.

  • If you're using a Signalink in Direwolf, there is no PTT, as it relies on VOX. You will unselect #ADEVICE - plughw:1,0 (or some variation depending on what your soundcard shows up as). The numbers more or less mean USB bus location and item). For Linux users there is a lot of doucmentation on how to find this. For Windows, a little less. In my instance when using the Windows version (and interfaced with a Signalink). Direwolf automatically uses your sound card to trasmit here and you don't have to deal with excess PTT issues.

  • If you're using a Repeater Builder RIM, select: #ADEVICE USB. Make sure to uncomment the lines that you need. Uncomment means remove the # before each line that you want to activate. You can download a sample windows config file that will work with USB. Change to your settings:

  • Microphone and speaker levels are extremely important. You will need to go into Windows and adjust levels going in and out to make them "perfect". This is where it will take you the most time. Direwolf is great in that it tells you when things are too loud coming in. Output-wise, you'll have to watch and see if other gateways and igates are hearing your station. You will know when you show up on APRS.FI and other stations are moving your stations' traffic. Be patient and it will work!

  • Your microphone settings are your INCOMING signals from the radio/USB. Your speaker settings are your OUTGOING or TRANSMIT signals. Windows should recognize the new sound card interface and will let you adjust speakers independent of system sounds. On Signalink, Windows sometimes wants to use the USB Sound Codec for everything.  It is best that system sounds are routed NOT to your radio so we don't have Windows sounds on the APRS channel. Since the computer we're using is specifically for APRS and runs unattended, I shut system sounds off.

  • When using APRS or even VARA-FM, most of your time will be spent on setting system sounds. Learn to navigate the audio functions on your computers as once you get this down pat, everything else becomes easier. As a side note, your incoming sound will be considerably different than your outgoing sound settings. Make a note of them and don't just adjust them both at the same level. It won't work very nice. When using a Signalink, you have to be mindful of not only the computer volume settings, but the settings on the Signalink itself! Here are some links to various fun stuff.....

Hookup notes for Motorola Radios using RIM sound cards

Link to the RIM Maxtrac PTT Setup for Soundmodem  RIM MAXTRAC


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