One of the items on my seeming endless list of things to do in Amateur Radio has been to sort out a portable digital station. Other than a little WSPRing now and again I’ve only operated with any other digital mode (PSK31) once, just to try it out. That was three years ago with a Signalink USB and my IC-718. I’ve not touched it since however with my growing interest in portable operations I’ve wanted to add digital capability, especially when operating QRP. The portable digital station made its way to the top of the list with the recent acquisition of my KX2.
Even before the radio arrived I began to research digital operations with it. Obviously one way to do it is with the built-in functionality to both decode and send via the key, digital modes like PSK31 and RTTY. While this is a very nice feature and is clearly the lowest profile as it doesn’t require any additional hardware or software I wanted to have the ability to use a keyboard and perhaps a little large display than the scrolling one-line in the KX2.
The first approach that I thought I’d try was that of an Android tablet. We have a 7″ Samsung Galaxy 4 tablet that lies about largely unused in light of other devices. It’s certainly appealing due to its size, that being just a wee bit larger than the radio itself. I did a bit of research on this option and quickly found the DroidPSK app which is developed by Wolphi Solutions who also has have developed a simple tablet\smartphone to radio interface. A few more minutes research found that DroidPSK also can be used with a Signalink USB. The only downsides to this approach are that I’d need to carry a powered USB hub and I’d rather have a reasonable hardware keyboard as opposed to the soft keyboard of an Android app. The plus side was that I already own both the Signalink USB and a few powered USB hubs so other than the small fee for the app and some cables I was largely set. A nicer keyboard was kind of a sticking point though. The only time that I operated PSK31 I quickly found that I really wasn’t all that enamored with macro exchanges. I wanted to have an actual QSO, not just regurgitate canned messages. QSOs actually do occur in PSK31 but in order to facilitate this a half-decent keyboard was going to be a necessity. I realize that small USB and Bluetooth keyboards are available but that’s yet another piece of hardware to cart along and they are small, so I continued my research.
This past week, as I was sitting in my office eating my lunch and perusing QRZ.com I came upon a post by K5ACL entitled, “JT Modes & the Elecraft KX3, a how-to guide!” The post contained a video in which he described the use of a USB soundcard to interface to his KX3 in order to operate digital modes. Within minutes of watching the video I checked Amazon for the device, found it and ordered it, and as is typical, Amazon Primed it into my hands in two days. In between watching the video and ordering the USB soundcard, another dormant piece of hardware came to mind. We have an old Windows XP laptop that was purchased for the kids sometime ago, well before the days of smartphones and Android tablets. It’s small enough to be very portable and has a reasonable keyboard. With the addition of the USB soundcard it will make a nice platform for a portable digital station.
The USB soundcard that I purchased is a Sabrent. It gets very good reviews on Amazon and so for $6.49 it was worth a try. I plugged it into the XP machine and it had no issues. I quickly tested the input and output to make sure that it was working correctly prior to connecting it to the radio. When I purchased the KX2 in anticipation of digital operation I spent a few extra dollars to get their I\O cables, (E980229) Transmit Audio Cable and the (E980230) Receive Audio Cable. They are nicely done, with a right angle connector on one end and shrink-wrap colored labels that match their intended connections. The USB soundcard jacks are colored green for speaker\headphone (audio output from the PC) and red for the mic (audio input from the radio.) These match nicely with the labels on the Elecraft cables. The red plugs into the “phone” jack on the radio (audio output from the radio to the mic on the PC) and the green plugs into the “mic” jack on the radio (audio input to the radio from the speaker\headphone output.) The KX2 USB interface cable is used for radio control so you’ll need two USB ports.
KX2 PSK31 cables
Aside from the cable interface I set the KX2 to the “Data A” mode and dialed the power back to 5W as recommended by Elecraft.
Turning to the software, it seems as if the most popular PSK31 software is Fldigi, by W1HKJ, so I downloaded and installed that on the old laptop. If you are new to Fldigi, K4REF has a bunch of very nice videos on his YouTube channel that are very helpful.
The configuration of the software for my station is as follows. First, use the KX2 utility application to determine which com port is used by the KX2 cable to connect to the radio. In my case it was com7. Once that is complete shut the KX2 utility application down so that it frees the port for use by Fldigi.
KX2 com port
There are a lot of options in Fldigi. The most important ones to get right are the radio controls and the soundcard interface. When you first start Fldigi it will run a wizard which will step you through the settings. For my PC and the USB soundcard the configuration was a follows:
USB soundcard config
It’s possible that this may be different for your computer depending upon the sound devices in your PC. In XP you can check the audio devices by going to the Control Panel, double-clicking “Sound and Audio Devices” clicking the “Audio” tab, and then clicking the drop-downs for Default Device in both Sound playback and Sound recording. When I plugged in the USB soundcard they both defaulted to “USB Audio Device.”
There are several options for control of the radio. I chose to use Hamlib. My configuration was as follows:
Radio interface config
There wasn’t a selection in the rig list for KX2 so I chose the KX3 as they are likely the same for the purposes of rig interface for PSK31 operation. Set “Device” to the com port that the KX2 is on, in my case it was COM7.
Next I set the mode to USB and BPSK31:
And finally I entered the Operator settings (Configure\UI\Operator):
Fldigi operator config
As soon as the soundcard settings were complete signals started to appear on the waterfall and be decoded. In order to check my transmission I picked a clear spot on the waterfall and transmitted a test message to check the soundcard levels and adjust the mic gain on the radio to the 4-5 bars of ALC as recommended by Elecraft.
After a quick check of the macros, I looked for someone calling CQ. One of the first signals that I found on 20m was that of VY2PLH. This is a special callsign for lighthouse activations on Prince Edward Island. In this case the operator, Bernie, VE9BGC was operating at Point Prim Lighthouse. According to their site, Point Prim Lighthouse was built in 1845 and is the first and oldest lighthouse on Prince Edward Island. We had a nice exchange with good signal reports. A very nice first QSO with the KX2 digital station.
Thus far I pretty happy with this configuration. The only new piece of equipment I needed was the $6.49 USB soundcard. The laptop is small enough to fit into the small backpack with the KX2 so this should work well. Now I will have some digital capabilities for our next camping trip.