Over the weekend I tried my hand at some digital modes with the bitx 40. I was really wanting to try out PSK31, but I couldn’t find any on 40 meters. I did run across plenty of RTTY though.
First, I needed to get the bitx talking to the computer. I tried rigging it up to three different laptops, but I had no luck. I even built a board to split the TRRS connectors into separate line in and out jacks with full on audio transformers and everything, but I still couldn’t get it working correctly. In the end, I set up a raspberry pi with a usb sound card.
I installed the most recent version of raspbian, but the repos have an old version of fldigi that doesn’t have the raspberry pi rig control feature, so I needed to compile the current version of fldigi. What I was looking for was this:
Using the GPIO rig control feature, I can trigger a transistor from one of the raspberry pi’s GPIO pins to engage the push to talk on the bitx.
I already had a headphone jack built into the bitx, so I just plugged that into the line in on the usb sound card. I soldered a 3.5mm plug to the mic in on the bitx board and ran that to the output of the sound card.
That was pretty much it. I was able to transmit and decode RTTY with no problems. I did end up overclocking the pi to give it a bit of a speed boost because fldigi started to stutter a little.
Here is the final layout with a look at my messy desk.