When googling “packet radio soundcardmodem” you normally find solutions, which use Paxon with FlexNet. Unfortunately, FlexNet is very old and difficult to run on Windows 10. Due to this situation I searched for alternatives and found Dire Wolf. This soundcardmodem is still further developed and can be used on Linux and Windows. As terminal I stick with Paxon since I like its interface and it supports Windows 10.
Dire Wolf installation
After downloading Dire Wolf, extract the contents of the zip archive to start the program by double clicking on the direwolf.exe. Dire Wolf will start with its default configuration and uses your standard audio devices. Later you must configurate the PTT interface (in a config file) but this is not necessary for the first test (continue with 3. Paxon installation). When Dire Wolf is running it should say “Ready to accept AGW client application 0 on port 8000 ...”. We will use this socket to connect the soundcardmodem via Paxon.
Using RS232 for PTT
It is recommended to not use VOX for packet radio since VOX has a "turn on" and "turn off" delay. This means that transmission may start to late and only a uncomplete package is sent. Even worse is the "turn off" delay. It may cause interference between packet radio stations because the VOX-station transmits a unmodulated carrier for some seconds after the actual data transmission. This so called "VOX-delay" is important when talking into the microphone (you make breaks when speaking where the transmitter should stay on) but in a packet radio system this is bad. Due to that one could use the control lines of a serial port for PTT.
First you need an serial port on your PC. It is common to use a serial to USB adapter if you have none. After plugging in the adapter, the number of the new serial port should appear in the devices manager. Remember this number (e.g. COM6) because you need to write it into the Dire Wolf config file (direwolf.conf). The control lines DTR and RTS are available for PTT and can be inverted if necessary. The following line would configure COM Port 6, DTR for PTT at RS232 logic level "low" (positive voltage):
PTT COM6 -DTR
This line can be uncommented in the "direwolf.conf" file. The "-" indicates that the signal is inverted. For configuring Dire Wolf I can really recommend the official User Guide which is available on the Dire Wolf github page.
For installing Paxon just follow the installation program you downloaded (leave the standard options). Then start Paxon and klick on “Options”. At the “General” page you should add your callsign. Then switch to the “Devices” page and add a new device of the type “AGWPE”. Now click on properties and you should see that the host is set to “localhost” and the port is 8000 (password and username must be empty). These options are correct and standard. After clicking on “Apply” the device status should change to “Ready” (Dire Wolf must be running). Exit the options by clicking on “OK”.
Now it should be possible to connect to another station by clicking on the “Connect” button in the top left corner of Paxon. After starting the connecting process, you should hear “packet radio sounds” from your speakers. If you have two computers, you can connect them via two audio cables to fully test the data transmission. I did this with a Windows 10 laptop and a Linux laptop which both run Paxon with Dire Wolf. Furthermore, I will write an article about installing Paxon on Linux by using Wine in the future.
After a successful first test you can now add the PTT configuration descried under 2.1.
Paxon crashes if it “hears itself” on Windows. Dire Wolf can receive while transmitting and Paxon does not like this. When building the radio interface this must be considered. (Edit: The crash happens when Dire Wolf is restarted while Paxon is running.) In addition, when a connection is established Dire Wolf sometimes outputs an error when transmitting but so far this did not affect anything negatively.
Finally, I will describe how I connected my laptop to my radio in the next article of this series (soldering an interface).
Note: I used a German Paxon installation, so I do not know if the English button names are correct.