This section will describe setting up the VX-4000V radio to be used for packet operations combined with a laptop running Dire Wolf.
The radio has a 25 pin D-Sub connector on the back which will be used to get audio in and out of the radio and control the PTT.
Pin 11 is the PTT pin. When pulled to ground it puts the radio in transmit. When floating it is in receive mode.
Pin 13 is the digital input pin.
Pin 17 is the digital output pin.
Pin 7 and 18 are Logic ground.
The D-Sub connector is broken out with an adapter board, and then connected to a TRRS breakout to be connected to the laptop. This iteration does not include PTT control.
I tested this using Dire Wolf running on a Chromebook running Gallium. Using APRS.fi I didn't see much traffic so I used an android phone running APRSdroid and a Baofeng UV-5R connected with the BTECH APRS-K1 Cable. This is not the cleanest solution as it requires using VOX on the radio. The radio ends up transmitting for longer than needed. After messing around with settings in APRSdroid, I was able to see packets in Dire Wolf! I was also able to using Xastir to map the packets. The next step is setting up PTT!
My next step is setting up PTT so I can transmit APRS and other digital modes like WinLink or SSTV. I ended up going with a CM108 based USB soundcard for around $10. I looked into more finished solutions like the Master Communications DRA series, but ultimately went with the more homebrew solution. I also wanted to build it with some sort of standard connector to allow easy connection to multiple radios.
I bought a custom audio cable kit from Zap Cables as this came with the TRS connectors, cable, heatshrink, and paracord to make it all look nice. I used a GX16-5 connector on the other end to allow for multiple different radios to be attached. The GX16-5 connectors are easier to solder than the TRS connectors. The CM108 card only has a mono mic in which is connected to both the tip and ring of the TRS connector. I cut the traces to the ring and added a transistor to pull the ring to ground for PTT. The transistor is controlled by GPIO pin 3 VERIFY as this is the easiest pin to solder. The whole assembly is covered in hot glue and heatshrink to protect it.
The first trace cut
The second trace cut
The added transistor to allow PTT