WSJT Digital Modes with WebDX on Mac

You are here:
< Back

This document will layout the process to operate WSJT (and in theory any digital mode) using WebDX ONLY.

What can I do with WSJT?

Weak Signal Joe Taylor (WSJT) is software written by Nobel Prize recipient K1JT designed to decode extremely weak (-30db below the noise) signals. There are a number of “modes” that are designed for different types of propagation.

JT65A – 60 second sequences – This mode is very popular on HF, 6M and EME for long distance contacts.

MSK144 – New high speed meteor scatter – Very popular and very effective real time 6M meteor scatter, good up to 1500 miles.

JT9* – New modes which are gaining popularity.



  1. Lets start with making sure your mac has the time synced properly. If this is not already set you should always set this up.
    1. Open System Preferences then go to Date & Time. If your have the little security lock locked at the bottom, click to unlock, enter your mac password. Once unlocked make sure you have the “Set date and time automatically” checked. Good, now your mac’s clock will always be extremely accurate.
    2. Download, purchase and install the LoopBack digital audio cable software. When you purchase the software you will be emailed a serial number to unlock the software, I highly recommend that you save this information in a safe place.
      1. Open the LoopBack App.
      2. Rename the first device to “WebDX RX” and set the appropriate options.
    3. Click the + sign at the bottom left and create a second device and name it WebDX TX.
    4. Setup WSJT. This step is a little more involved, take your time and you will be fine.To do: <create video tutorial>
      1. From the Readme file located in the installer.

There are some system matters you must deal with first. Open a Terminal window
by going to Applications->Utilities and clicking on Terminal.

Along with this ReadMe file there is a file: sysctl.conf. Drag this file to your Desktop.

WSJT-X makes use of a block of memory which is shared between different parts of
the code. The normal allocation of shared memory on a Mac is insufficient and this
has to be increased. You can check the current allocation on your Mac by typing:

sysctl -a | grep sysv.shm

If your shmmax is already at least 33554432 (32 MB) then you can close the Terminal
window and skip the next steps and go to (NEXT).

Now move this file into place for the system to use by typing: (Note this assumes that
you really did drag this file to your Desktop as required earlier.)

sudo cp $HOME/Desktop/sysctl.conf /etc/
sudo chmod 664 /etc/sysctl.conf
sudo chown root:wheel /etc/sysctl.conf

and then reboot your Mac. This is necessary to install the changes.

You are now finished with system changes. You should make certain that NO error messages
have been produced during these steps. You can now close the Terminal window. It will
not be necessary to repeat this procedure again, even when you download an updated
version of WSJT-X.


Drag the WSJT-X app to your preferred location, such as Applications.

You need to configure your sound card. Visit Applications > Utilities > Audio MIDI
Setup and select your sound card and then set Format to be “48000Hz 2ch-16bit” for
input and output.

Now double-click on the WSJT-X app and two windows will appear. Select Preferences
under the WSJT-X Menu and fill in various station details on the General panel.
I recommend checking the 4 boxes under the Display heading and the first 4 boxes under
the Behaviour heading.

5. Open Chrome and log into the RHR console. Once logged in go to Settings -> Set Mic and Speakers

Once set, click done and then refresh the console screen. The refresh is needed in order for Chrome to use the newly selected Mic device (WebDX TX). As a note, you can switch the output device on the fly without a refresh.

6. Open WSJT. Once open, click WSJT-X then Preferences. We need to set the General and audio tabs. **Note: Be sure to change the “My Grid” field when operating RHR stations. The grid square of the RHR station is clearly shown in the station tab.



7. Connect to a RHR site. Here are a few things you should do once connected.

  • Set CMP (compression) to 0 – You don’t want compression on TX.
  • Set Radio mode to USB
  • Open the BW to full 4Khz
  • Set AGC-F or AGC-OFF for full dynamic range (if AGC-OFF selected we cut the RX audio level down by 50%)
  • Make sure NB/NR are off
  • Setting the RX audio level is important. You will want to adjust the RX volume and the audio slider in WSJT so the audio level is 30db (see screenshot below).
  • Click the VOX button so it lights up YELLOW, VOX will now be enabled. The VOX badge is located just below the BLUE POWER ON button.


9. At this point you should start to see traces in the panadapter on RX and you should be able to TX as well!


10. Logging with RHR Logger (Also useful for LOTW). When logging with the built in RHR Logger, above the “NOTES” field is a mode pull down menu. Pull this menu down and select “DATA” for the mode. When you enter contacts into the logger they will be uploaded as DATA and will match in LOTW. Also note the signal report is not used for log checking so you can simply leave those fields default 59. Here is a confirmed LOTW contact.


*** This is new territory, please report any bugs, corrections or additions to support so this article can be updated.