How To Set Up WSJT-X With An Elecraft KX2 Transceiver For FT8 Using A Windows 10 Laptop PC Without An Additional External Soundcard (And An RC Crawler SOTA Adventure)

[Jump here or scroll down if you just want to get started with the instructions on how to set WSJT-X up on the Elecraft KX2 transceiver.]

I messed up. I could not get the KX2 to transmit in SSB yesterday. On a truly beautiful spring afternoon AA1F, Georgie (our shepherd), and I set out to do two things: 1) drive our 1:10 scale RC crawlers up Tully Mountain (W1/CR-012) , and 2) get a single SOTA point.

Mine, the clear one, is a build on a Vanquish VS4-10 straight axle chassis kit. AA1F chose the Vanquish Optic H-10 to put together. Interestingly, he did not pick the color. Vanquish makes you buy the kit before you know which hue is yours. It seems pretty fitting though doesn’t it?

The trail up Tully Mountain in Royalston, Massachusetts is a very humble 2.5 mile round trip (if you take the “gradual” way up and down. The “steep” way is actually rather steep.) Tully Mountain is a part of the much longer Tully Trail which AA1F and I did as a grueling day hike a decade and a half ago. This corner of the world means a lot to us. Our recently built little trucks have been breaking down on every run we’ve taken them on, and we were hoping they would be dialed in enough this time to get up and down the hill without fail.

We ran in to a few obstacles to climb along the way. Like that one above. And this one below.

Ultimately the RC crawlers hiked the entire way without issue (yay!) Unlike my operation of the KX2…

Let me back up a bit. A couple of months back, I got it in my head that I wanted to be able to use the KX2 on digital modes. This meant fiddling with a whole bunch of settings trying to get it to work. I suspected when I attempted to call CQ on upper side band yesterday and I was getting no indication of power out on the RF meter, that I had forgotten to change something back. After we returned home from the trip last night, I began troubleshooting and sure enough I had messed up a setting on the radio (I’ll explain later). If I had only documented how to do digital modes on the KX2 here in this blog, I would have been able to reference it and easily correct the problem while still up on the mountain. Oh well, better late them never. So here goes!

How To Set-Up Digital Modes With WSJT-X On The Elecraft KX2

How Does FT8 Actually Work?

First off, what is it exactly that we are doing when we operate FT8 with any radio? In general, we are using the WSJT-X software suite to encode our 13 character (maximum) message with a process that uses a type of frequency shift keying (FSK) to generate a 174-bit codeword composed of arrays of 8 different audio frequency tones. This newly created audio frequency codeword (which contains the original 13 character message) is then passed through a digital-to-analog converter of a computer soundcard to create an analog signal. The analog audio frequency signal is then modulated onto an upper side band (USB) carrier that can then be transmitted via RF by a radio transmitter. The now propagated RF signal with the FT8 codeword modulated onto an USB carrier arrives at a radio receiver which then demodulates the USB signal back to its original analog audio frequency tones. These audio frequency tones must now pass through an analog-to-digital converter of a computer soundcard, where they are digitized. The digital audio frequency codeword is passed to a the WSJT-X software suite which further demodulates the 8-tone continuous phase FSK signal (8-CPFSK) back to the original 13 character (or less) message. Please note, that this is *my* understanding of how FT8 works; this may be flawed and I suggest you do your own research.

What Is Needed To Operate FT8 With An Elecraft KX2 Transceiver?

Now that I described how FT8 works, it should be pretty easy to figure out what is needed in order to operate FT8 with a KX2. Let’s think this through. In order to encode the 13-character message into a digital FT8 signal, we need WSJT-X software. Of course we need a computer to run this. We then need a sound card with its usual digital-to-analog converter (DAC) to take that digital audio signal and convert it into an analog signal. We need some sort of cabling to get this newly created FT8 analog signal to the KX2, so that the KX2 can convert the audio signal into an USB RF signal in order to transmit. Then, when we receive an encoded RF signal containing an FT8 message, the KX2 will demodulate it back into analog audio. We will then need more cabling to get that analog audio signal through the analog-to-digital converter (ADC) of the sound card, and then back into the WSJT-X software to decode the now digitized audio signal into its original 13-character message.

EQUIPMENT

• Elecraft KX2 transceiver
• Computer (Note: these instructions are based on a Windows 10 PC laptop) with a USB port, a single speaker/mic combined jack, and an internal soundcard).
• WSJT-X software
• Soundcard (Note: these instructions are specifically for a laptop PC with an internal soundcard; no external soundcard is required)
• (#2) Two 3.5 mm TRS-to-TRS audio cables. An example here.
• (#1) One 3.5mm speaker-mic audio splitter. An example here. (Note: This device specifically is meant to take a single 3.5mm speaker-mic jack on a laptop PC, and split it into separate 3.5mm speaker and microphone jacks. Be careful buying this! The one I linked to is the exact one I am using.)
• KUSB-A CAT control cable. (Note: Just get this one.)

How Do You Hook Everything Up?

The diagram above shows exactly how to do it. As a caution, it is best to do this after you’ve adjusted your KX2 settings though (see below). I have been able to get the KX2 to autonomously transmit by connecting the cables before the settings were changed which is obviously not a good thing.

The TRRS plug of the KXUSB-A cable feeds in to the ACC jack of the KX2. The USB-A plug of the KXUSB-A cable attaches to a USB port on your computer.

The TRRS plug of the speaker/mic splitter attaches to the combined speaker/mic jack of your PC. If your computer has separate speaker and microphone ports, you do not need the splitter! One end of one of the TRS-to-TRS audio cables plugs into the speaker jack of the splitter, and the other end plugs in to the microphone jack of the KX2. One end of the other TRS-to-TRS audio cable plugs into the microphone jack of the splitter, and the other end plugs into the headphone jack of the KX2. Just think it through, sound comes out of the KX2 through the headphone jack and goes in to the computer (sound card) through the microphone jack. And vice versa.

These are the ACC, Phones, and Mic jack on the side of the KX2.

This is the KXUSB-A inserted into the computer. This is also the speaker/mic splitter.

What Settings Do You Need On The KX2, Computer, And WSJT-X?

KX2 SETTINGS

MODE: DATA A (Note: Press the DATA button. The “A” refers to the use of the upper VFO frequency.)
NB: OFF (Note: noise blanker NB, noise reduction NR, and pre-amp PRE settings are all in the bottom left of the KX2)
NR: OFF
PRE: OFF
RF Gain: 0 (Note: Long press “DISP” in the bottom right corner to adjust this)
FIL BW: 4 kHz (Note: Engaging “DATA-A” mode will already set this. But once in DATA-A, press the “FIL” button in the lower left and then use the left-most knob to adjust. See pic below).
FIL Center: 1.5 kHz (Note: As far as I know this is automatically applied when going into DATA-A mode. I do not know how to adjust).
AF: 2-10 (Note: AF, or Audio Frequency, is essentially the volume button. When receiving FT8 signals, monitor the scale on the bottom left of the main WSJT-X window. You do not want this in the red! The scale should be green. See pic below.)
AGC MD: OFF (Note: Make sure to turn it back on though for SSB and CW! Long press “DISP” in the bottom right corner to adjust this.)
AGC LIM: 20 (Note: I am not sure if this matters if the AGC is off. Long press “DISP” in the bottom right corner to adjust this.)
MIC GAIN: 0-50 (Note: The Mic Gain is tricky. Essentially, you want 4 to 5 bars of ALC when transmitting FT8. When FT8 is transmitting, adjust both the “PWR” slider in the bottom right of the main WSJT-X window and the Mic Gain knob which is the second one in from the left of the KX2. Make sure you are displaying the ALC meter and not the RF meter that it toggles with.)
PWR: 5 to 7 watts (Note: Monitor the KX2’s internal temperature; see pic below. Long press and turn second knob from the left.)
MIC BIAS: OFF (Note: If you do not turn this back on and you are using the supplied KX2 microphone, then you will not be able to transmit voice SSB signals! THIS IS WHAT I SCREWED UP!!! Long press “DISP” in the bottom right corner to adjust this.)
MIC BTN: OFF (Note: If you do not turn this back on and you are using the supplied KX2 microphone, then you will not be able to transmit voice SSB signals! Long press “DISP” in the bottom right corner to adjust this.)
VOX: ON (Note: Turn this off when you are done with FT8! Long press “DISP” in the bottom right corner to adjust this.)
RS232: 38400 b (Note: This baud rate must match the one you program into the WSJT-X software. Long press “DISP” in the bottom right corner to adjust this.)

Below are some photos of some of these special KX2 settings:

The ALC, or Automatic Level Control, helps create a consistent signal volume. In order to do this, the volume inputted into the radio needs to be at an ideal level. By monitoring the ALC, you can find the right signal volume going from your computer into the KX2. Ideally, aim for 4 or 5 bars. When the KX2 is transmitting FT8, adjust both the “PWR” slider on the WSJT-X software and the Mic Gain knob (shown below) to achieve the correct 4 to 5 bars of ALC.

The filter width is also very important in FT8. You switch to DATA-A mode by putting the KX2 into USB mode and then pressing the “DATA” button; you can then see the arrow pointing upward toward “A” and “DATA” on the right hand side of the display telling you that you are in the correct mode. This should automatically open the filter to 4Khz, but you can check this by hitting the “FIL” button (which is underneath my finger) and then turning the left-most knob. The “BW” display will say 4.00 for the 4KHz filter, and the filter schematic will be at its widest.

It is also very important to monitor the KX2’s internal temperature in order to make sure that the transceiver is not overheating given FT8’s full duty cycle. In order to turn on the KX2 thermometer, hit the “DISP” button in the lower right and then turn the right-most knob, known as the VFO-B knob. When the “PA.I” display shows up, this is the KX2’s temperature in Celcius. “PA.I” stands for “Power Amplifier – Internal”. Once the KX2 reaches approximately 60C, it will roll back transmit power automatically to 5W or less. I personally try not to let the KX2 get much higher than 40C before letting it cool down. If it does get too hot, STOP TRANSMITTING!!!

When receiving FT8, monitor the bottom left scale. It should be green (not red as shown) in order to eliminate distortion. Use the AF Gain knob (outer left) to adjust the volume into the computer sound card.

COMPUTER SETTINGS

You need to make sure that your computer audio settings are set up correctly as well. First, make sure you turn off your system sounds. Notice the little “x” by the speaker icon next to the “System Sounds” below. This is to avoid transmitting the boops and beeps that a PC makes. Next set the speaker volume somewhere around 50%. My master volume is at 40% and that seemed to work fine. There are a lot of different places where sound settings hide on a PC. I hate to say it, but you may just have to play around with this a bit (hand waving, hand waving, hand waving…)

WSJT-X SETTINGS

Finally, and fortunately fairly easily, the WSJT-X settings are easy. I am assuming that you already know the basics of using FT8. In the Settings, you will need to set up the “General” tab, the “Radio” tab, and the “Audio” tab.

Radio Settings:

Rig: Elecraft KX2
Serial Port: COM[?] (Note: Go to the Device Manager and check the “Ports” section to see which COM Port your device is using. It probably will change frequently. In my case, the KX2 was in COM7. See pic below.)
Baud Rate: 38400 (Note: Remember to match this to whatever you set your KX2 to.)
PTT: CAT
Mode: Data/Pkt
Split: Fake It

You can find the correct COM port by typing “Device Manager” into the search bar and seeing which COM pops up when you plug your KUSB-A into your computer. Note, that for this screenshot, the KX2 is NOT attached to my computer, so the COM port does not show up.

Audio Settings:

You need to choose the correct Input and Output device. For my PC the speaker/mic jack uses the Realtek Audio devices. My KX2 was not plugged into my computer when I took this screenshot, thus they say “Not found.”)

One other mention though, you need to have a tightly synchronized clock on your computer in order to make contacts. Having access to an internet connection is helpful. I use the Meinberg NTP client as recommended in the official WSJT-X user documentation. An inaccurate computer clock is often the reason for not being able to make FT8 contacts.

That’s all! The entire set up is a laptop PC and four distinct cables. As you can see by the red below, I was able to make contacts. Running 3 watts!!!

Whew, we did it! This is a pretty comprehensive look at how to set up the KX2 to work with WSJT-X. I am sure there are other ways to do it, but so far these seems to be working for me!

Don’t overlook the weak signals!

KM1NDY