Using the ASUS WL-500gP as a APRS digi

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1 Prelude

Very recently I have purchased a Bosch KF-166 single frequency VHF transceiver which has been modified as a 144.800 MHz transceiver by the previous owner. He removed the tone control unit and did some other mods so that it really only transmits on the APRS frequency. The TRX PWR is 6 watts.

Since my old TNC2S was practically out of use for 15 years, this is a great opportunity to recycle it and turn it into a controller for APRS.

The APRS manager software will then run on my ASUS WL-500GP. There is the fabulous APRS4R project from Karlsruhe, which I want to give a try. Here are some important sources of information:

Eventually, I want to implement something similar as in this article:

Perhaps I will set up the planned APRS digi at DB0MHB, since the Münchshofener Berg has excellent propagation conditions, being 530 meters high. But this is still an open question, given the fact that my friends don't have a single ampere-hour to spare.

2 Soldering connections between the TNC2S and the KF-166

The main task was to solder a working connection between the TNC2S and the Bosch KF-166. I just unmounted the microphone handle and connected the cable to the TNC plug.

Aprs plug.jpg

3 Re-activating my TNC2S

Initially, the TNC2S didn't work. I found the reason: The EEPROM was loose. After sticking it in again, it worked fine. The KF-166 also proved well-configured, because I received lots of APRS signals right away. I controlled the PTT and the modulator connection by listening to it with my other VHF rig.

In any case, the APRS reception worked right away without any hassle. Here is a screenshot of my terminal program on my workstation computer. Needless to say that I am getting the same picture from my minicom program on the ASUS router.

Aprs first results.png

Off course, the messages are still very raw format and need to be processed somehow, but this all is going to be done by the APRS4R software on the router.

4 Connect the TNC and the WL-500gP

The next task was to connect the TNC and the router. It was a little annoying to make sure to solder all the connections right, but I finally got it.

Kf166 tnc asus.jpg

5 KISS Mode

The KISS mode (keep it simple, stupid) is an operating mode for the TNC that puts the burden of controlling the connecion to the computer.

In most cases you firstly needn't care at all about this mode. That's just some interesting information on what it is.

6 Running APRX

APRX is a receivong only Digi software that runs on OpenWRT. I got it running and it runs fine. Got some troubles composing the beacon message because I didn't know my GPS WGS84 position right off my head, but finally I got myself located in

7 Upgrade the RX digi to a TRX digi using aprs4r

aprs4r is a aprs digi software written in RUBY. Running it requires to install RUBY in the first place. As an alternative you can take the openwrt install image from the aprs4r project and install it right away on your machine. There's yet another way: The aprs4r project offers a shell script that cares for the download and the entire installation of the software packages.

Have a look here: