Operating FT8 on the Elecraft K3

Last night on 30m

Last week, I put up a new HF antenna and this week, I set the station up to operate in FT8 mode. Below, I describe a minimalist implementation using an Elecraft K3, a computer and two audio patch cords. I am focusing only on items specific to the radio and not found in the WSJT-X documentation.

Why FT8?

Why FT8? First, because it is popular, which means that there are people at the other end listening (or sending). Since I have lived overseas since FT8 came out, just about everyone in the US is a potential new contact for me. This is a good chance for me to work on my digital WAS. Second, because my power output is limited, for a digital mode, I can’t go above 50W on HF. That’s something of a limitation for phone, but certainly not FT8. Third, and closely related, we’re nearing the bottom of a solar cycle. If I’m going to make contacts on the upper bands, I’ll either need some luck with sporadic openings or to run an error-correcting weak signal mode, or both. Finally, because there is often a lot of local EM noise. I can listen through it, particularly for CW, but turning the sound off and letting the computer sort through the buzzing is also attractive.

Why the K3?

Why the K3? It requires less equipment. Previously, I ran digital modes to my TS-2000 using a rigblaster nomic to provide isolation between the computer sound card output and the rig’s microphone input. However, the K3 has line in and line out ports built into the rear panel. Both of these ports are coupled via internal transformers, which means that both lines are galvanically isolated, not just audio input to the rig. It also means that I don’t have to either give up my front mike jack or wire up a complicated accessory port to get sound in and out of the radio.

Audio Connection

I am currently using a 2007 MacBook Pro to run WSJT-X version 2, so I am taking sound from its headphone jack and running it to line-in on the K3, and sound from the line-out jack on the K3 to the microphone input on the Mac. As with most computers, there is no line-level input on the Mac, so I needed to turn the Mac’s sound input sensitivity almost all the way down. In principle, I could have put a resistive attenuator inline, but I found that wasn’t necessary, so I saved myself the trouble.

To get the K3 to input sound from the back panel, it is necessary to go into the main menu and turn “MIC SEL” from its usual front panel mike jack setting to line input.

When the microphone selection is set to line input, the “mic level” knob on the radio’s front panel now controls the sensitivity of the line input. When you switch back to the front panel microphone, the previous setting of the microphone level is not affected.

The radio’s line output sound level is set by a configuration menu option, “LIN OUT”. I found that level 2 worked for me. Again, this setting is independent of the headphone/speaker settings, so you can dial the volume up or down, and it will not affect the level going to the computer (which is what you want).

VOX versus CAT

That’s the extent of my interfacing. I decided not to add a CAT control, although I could have done so through a USB-to-serial cable. I am using the K3 as my main CW contesting rig, so it is already plugged into another computer and I would rather not need to switch the serial line between computers. Instead, I am using VOX control, which works fine.

The trick with the VOX control is that the computer’s sound output has to be loud enough to trigger the radio’s audio detection circuit. The radio’s sensitivity is set by the main menu’s “VOX GN” setting, which runs from 1 to 100. To figure out where to set it, put the rig into test-transmit mode so that no signal goes out over the air (long press on the right side of the mode button). Then hit “tune” on WSJT-X to send a tone. Turn VOX GN high enough that the radio’s transmit is triggered and then dial it down to the point that the radio is no longer keyed. Then turn the vox gain back up a bit over that threshold to provide some margin.

Getting the audio levels right is a matter of playing with the computer’s sound card settings as well as the K3’s line in and out levels. The instructions for WSJT-X indicate that the program’s sound bar should show about 30% on a dead band, so I set the controls accordingly. As for output, it is affected by the computer volume level, the power slider in WSJT-X, and the line-in sensitivity knob on the radio. My goal was to set the level such that the ALC showed not more than four bars — the point at which ALC kicks in on a K3. Again, this meant putting the rig into “test” transmit mode and hitting WSJT-X’s “tune” button.

All settings that would distort audio should be off. So, on the transmit side, I turned compression to zero using the front panel knob. For receive, I turned off the AGC (first taking my earphones off), as well as the noise blanker and noise reduction. I dialed up the SSB filter to max width, which for me is 4 kHz. There’s no need for any sort of filtering or DSP — let the computer handle all of that as it sifts through the noise for FT8 signals.


At this point, the rig is ready to go on the air. Set the band within WSJT-X and then set the rig to USB mode and the dial frequency just as shown in WSJT-X. Also: don’t forget to make sure your computer’s clock is precisely synched. Although my mac is set to pick up internet time, I usually force a synch before an FT8 session by typing “sudo ntpdate -u time.apple.com” on the command line.

Before transmitting, make sure that reception works. If all has gone well and you’re on a band that isn’t dead, you should see signals on the waterfall and their corresponding decoded text within WSJT-X.

Folks have different philosophies about power level, but a practical upper bound is half the rated power of your rig. The K3 will do 100W, but for a full duty-cycle, I won’t go above 50W; on times are only 15 seconds, but if you are having a good day, the rig might not cool well with frequent cycles, and heat definitely does shorten component life.

I’m not advocating operating at that much power, though. Statutorily, you are supposed to use the minimum necessary for a given purpose. If your goal is DX contacts, that purpose might require more power, but if you are interested in more local QSOs, less power.

Luckily, some feedback is available to help you pick the right power setting: PSKreporter (and to a lesser extent right now, the reverse beacon network). Last night, I settled on 20W for 30 meters because I could see that at higher power I was being heard by stations that I could not myself hear, likely due to differences in background noise levels. It makes no sense to spam the airwaves with calls if I can’t hear the reply. This method isn’t perfect since I don’t know how much power the other stations are running, but it’s a rough guide.

Here’s what I heard last night on 30m. I think the Pacman shape of my receive pattern is mostly due to lack of stations in that part of the Atlantic.

Similarly, for DX, having higher power is probably less important than finding clear bandwidth and being properly time-synched with respect to the other station. It’s not like the other station is listening for the loudest signal on a single frequency — it will probably respond to the first intelligible signal it detects anywhere in its passband (although the timing may be more random if it’s operating in DXpedition mode).

With this set up, I was able to fairly consistently pull fish out the pond, one after another for hours. I’m sure that will drop off as more people have me in their logs, but it was reassuring that the set up works as designed.

Addendum: Ben, NN9S, shared with me his set up notes for the way he has set up his K3 and KX2.

Physical connections:

  • Macbook is sync’d to atomic clock — check in System Prefs.
  • External Soundcard (iMic)
  • Attach to Macbook, make it the ‘primary’ sound interface in System Prefs — set input to ~75%, output to ? 50%. (Adjust later)
  • In ‘AudioMIDI Setup’ app, set iMic device to: 48khz 16bit 2 channel
  • iMic soundcard has 1/8″ patch cables going into:
  • KX2: headphones and mic jack, both 1/8″.
  • K3: audio “in” and “out” ports in the rear, both 1/8″.
  • Rig-control cord goes from Macbook USB port to
  • KX2: the “ACC port”, which looks like a stereo 1/8″ jack — via custom elecraft cable. Assumes Macbook has the proper cable FTDI drivers to create virtual com port.
  • K3: the “RS232 port’ — use 9-pin RS232-to-USB cable. Drivers at Prolific site.

Radio Settings:

  • Set to USB, then DATA mode.
  • Set band to 20m (14.070) or 40m (7.074). Tune a bit away, then use ATU to get low SWR.
  • Turn off AGC completely:
  • KX2: change “AGC MD” in settings — this disables the ATU!
  • K3: long press the dedicated AGC button to turn it off.
  • Maximize bandwidth (‘FIL’ter button) to 4.00 khz
  • Set tx power to 10 or 12 W (to start)
  • Set AF output to ~30
  • Set Mic level to ~20 (?)

WJST-X Preferences / Settings

  • General: NN9S, grid EN71. Check all but last Display checkboxes; check all left-side behavior checkboxes.
  • Audio: set to iMic external sound interface!
  • Radio:
  • For KX2 Radio: set rig to ‘elecraft k3/kx3’. Serial port shows up as /dev/tty.usbserial-AH03HO9Q. Set 4800 baud, 8 data, 2 stop, no handshake. PTT method CAT. Mode ‘none’, Split ‘none.’
  • For K3 Radio: set rig to ‘elecraft k3/kx3’. Serial port shows up as /dev/tty.usbserial. Set 9600 baud, 8 data, 1 stop, no handshake. PTT method CAT. Mode ‘none’, Split ‘none.’
  • “TEST CAT” button should turn GREEN when pressed.

Configure FT8 in WSJT-X software:

  • Make sure it’s set to Mode FT8 (Mode menu)
  • Set Tx and Rx frequencies to 1200hz; bin/pixel=4, start=200, n avg=2
  • Click MONITOR to start listening
  • Set AF gain on radio (and iMic sensitivity control panel) so that overall lower-left noise level is about 30db.
  • KX2: What worked on 12/23/18: iMic microphone set to 25% input volume, KX2 AF gain set to 15. Probably depends on the daily amount of noise on band.
  • K3: On 12/26/18: use LOWER RF knob on K3 to set volume into iMic; iMic set input to 25%.

Addendum: Screenshot from WSJT-X settings for rig control of K3:

17 thoughts on “Operating FT8 on the Elecraft K3”

  1. Hi George,

    No, not yet. I haven’t even tried JS8 call yet. For the moment, just about all my HF equipment is in transit to Cyprus. Once I get set up again, though, I would like to give JS8 call a try.



  2. “Set to USB, then DATA mode”

    What that means???

    I’m running a K3 with WSJT-X 2.1.0.

    On 20m I can RX (decode) the signals with DATA
    On 40m I can’t RX (decode) any signals with DATA. It is working with USB.

    So I’m a little bit lost.

    Daniel, HB9DDS

  3. Hi Daniel. This part was from my friend Ben, NN9S. I think what he meant was to press the mode button enough to get to “DATA”. That will center the filters in the pass band.



  4. I cannot get WSJT-X to connect to my K3, I keep getting an erro message ” Rig Control Error” “Hamlib:IO error while opening connection to rig. What am I doing wrong.
    Bill AA4MJ
    Email: bthomp1936@gmail.com

  5. Hi Bill,

    Could you let me know what kind of computer, operating system, and software you are running? My K3 is currently connected to a Windows 10 machine running WSJT-X version 2.0.1, which is probably the most common situation. I’ve pasted a screen shot of the settings tab from the WSJT-X program so you can see what is currently working for me. As far as I know, I have made any unusual settings to the K3. As for the COM port, you will have to see which of your serial ports (or virtual serial ports as the case may be) are in use, and if you aren’t sure which goes to the rig, work it out by experimentation).

    I’ve had success running FT8 on Macs and Linux boxes as well.

    In a pinch, you could just entirely dispense with CAT control — in a sense it isn’t needed. Just set the dial frequency manually and put the radio in VOX mode. VOX is fast enough to trigger off the audio output from your cmoputer. This set up wouldn’t be ideal, but at least it would get you on the air.



  6. Hello Jack
    I am using a Dell computer running Windows 7 Professional. I am using WSJT – X v2.2.0 6a6ce4.
    I have set all the parameters you have in your screenshot. I only have the option of selecting K3 for the radio. I do not have an option of setting K3/KX3. I have tried all my Comm ports. I use Comm Port 1 for running PSK. When I test CAT I still get an error saying my rig is not connected to WSJT-X. I have the K3 set for 14. 074.00 but get nothing when decodes flashes.
    I am using Ham Radio Deluxe as my rig control and logging program.
    Any suggestions?
    Bill AA4MJ

  7. Got FT 8 working. Just had to put Ham Radio Delux in the Rig screen instead of my Elecraft K3.

  8. Thanks for leaving the comment – I have HRD on the rig that I use for satellite, but hadn’t tried FT8 on that rig yet, but I am sure I will at some point! 73 – Jack

  9. Thank you! I am going to try this mode again with CAT instead of VOX at my new QTH. I tried it a few years ago and lost interest. Things for me have changed and I need to try this again. I found that your step by step, here’s how you do it, guide to be very helpful. About power level, I thought that most were running at the most 10 to 15 watts. Is that not correct? A few years ago I did a YouTube video using a light bulb as the antenna and made several QSO’s. I have no idea what the ERP was but it could not have been more than a few milliwatts. I should try that again. I recently made a light bulb dipole antenna for another video. Thanks again for the excellent help. 73, Jim W6LG

  10. Mu bien su explicación Jack
    Al principio funcionó muy bien y hice bastantes contactos. Pero ahora me parece que no sale señal del K3s, mi computadora es un PC.
    En un principio me funcionó pero ahora llamo CQ y no me contesta nadie, probare de poner los ajustes otra vez.

  11. Hi Jim,

    Initially most operators stuck to low power settings, but there certainly has been creep because just about everyone sticks to the default band, which becomes carpeted end-to-end with signals. FT8 is good at picking out overlapping signals, but the stronger signals do have an advantage. When there is DX, the knobs get turned to the right, and signals go out on par with RTTY. I suppose that there is nothing inherently QRP about FT8, but I do kind of wish there were some self-policing in terms of power output. I think the only alternative is to operate smarter — get to band openings before others, trying spinning the dial a bit and operating split, etc.



  12. Hola: asegúrese de que la configuración de salida de sonido de su K3 sea correcta (por ejemplo, seleccione “salida de línea” en el menú de configuración y ajuste el nivel de sonido). ¿También podría ser un problema con la configuración de entrada de sonido de su PC? ¡Buena suerte! 73- Jack

  13. Hi Jack,

    I just spent literally hours and hours trying to configure WSJTX to work with the K3 WITHOUT CAT control as you did.

    A SUPER IMPORTANT point left out of the article is that the Rig should be set to NONE under the Radio tab of WSJTX.

    This is CRUCIAL because otherwise the software will continue to give a rig error message as the software continues to try to communicate with the radio (but can’t since there is no USB connection(.

    Took me HOURS to figure that out.

    Hope to save the me the guy endless frustration.


    Bob AA6VB

  14. I followed your suggestions, but I use the CAT control.
    Everything works correctly but the radio when it is the transmission turn, goes in tx but does not transmit anything and the power indicator remains at the minimum even if I have set 50w.

    Any suggestions?

  15. The most likely issue is that the radio is not seeing an audio signal to drive output. I would start at the computer and make sure it is output sounding. If that is the case, check the wire to the computer, make sure it conducts sound, make sure it is plugged in correctly. Relevant menu settings include selection of line input and the level of that input. If there is sound coming into the radio, you should see some deflection. I don’t have this rig in front of me just now, but I think you could also listen by pressing the monitor button to hear the input audio. Good luck!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.