Preview: Beta Testing phase

SOTACAT is a small hardware module that plugs into an Elecraft KX2 or KX3 radio’s CAT port (Computer Aided Transceiver port, also known as a “serial port” or an “accessory port” or “ACC port”) and provides WiFi control of the radio from your mobile device. It provides the following features:

  • Control your radio from a web page on your phone:
    The SOTACAT acts as a WiFi hotspot in the field with its own web server and mini web site. Connect your mobile device to the WiFi SSID “SOTACAT_xxxx“, in the field or at home and then use your phone’s browser to navigate to http://sotacat.local (Android users might need to use instead if your phone doesn’t support mDNS / Bonjour Service). You’ll see a web site that can control your radio!
  • SOTA/POTA Click-to-Pounce:
    When cell service is available, it allows SOTA and POTA operators to “click-to-pounce” from your mobile device. You’ll see a list of current SOTA and POTA spots and clicking on any spot automatically tunes the radio to the correct band, frequency, and mode to start a contact with that operator.
  • SOTAMAT spotting over HF with direct FT8 Synthesis (audio free!)
    Rather than playing FT8 audio from your cell phone speaker into your radio’s microphone, SOTACAT allows you to self-spot with SOTAMAT by teaching the Elecraft radio to directly synthesize FT8 signals audio-free. This is direct FSK without any audio signal, microphone, or audio cables. SOTACAT accepts FT8 message strings from SOTAMAT (or any other app via a SOTACAT WiFi REST API) and computes the FSK encoding required to implement that FT8 message. The cell phone’s clock is used to get the FT8 timing correct for transmission by the Elecraft radio.
  • Additional SOTAMAT integration:
    SOTACAT forms a bidirectional connection with the SOTAMAT app on your phone allowing SOTAMAT to read what operating frequency and mode you have selected and automatically picking the closest setting from your SOTAMAT configuration. Making a change to SOTAMAT’s frequency / band selector will, in turn, adjust the radio’s operating frequency/band/mode. Once you enter your peak or park ID (or use the automatic peak/park selector via GPS), SOTAMAT will use the SOTACAT to send the proper FT8 message to self-spot, self-alert, or send an SMS/eMail message command. It easily allows your operating band to be different than your FT8 self-spotting band: the SOTACAT will automatically do all the work!
SOTA and POTA “Click-to-Pounce” operation

Bi-directional SOTAMAT and SOTACAT integration

Current status

  • The following are available on Github:
    • Written instructions for manually building your own SOTACAT, including the Bill Of Materials / Parts List, Schematic, and Assembly instructions
    • Pre-release firmware. Things are very much in development.
    • Links to Beta versions of the SOTAMAT app that are SOTACAT aware.
  • YouTube build instructions video showing how to manually build your own SOTACAT
  • There are at least 2 other hams (K5EM and KE6MT) who have created custom circuit boards that implement a SOTACAT in an even more compact and professionally designed package. Stay tuned.

Installing Firmware

You can load the latest official software (known as “firmware”) into your SOTACAT as follows:

  • Visit this page with a supported web browser. Only the following browsers support the required “Web Serial” standard:
    • Google Chrome
    • Microsoft Edge
    • Opera
  • Connect the SOTACAT to your computer with a USB cable. Many USB cables only support charging and lack the extra wires needed for transferring data. If the steps below don’t work, try again with a better (often thicker) USB cable.
  • Once powered on your SOTACAT will go to sleep after 60 seconds without a connection. You have 1 minute to complete the following tasks.

    If your device goes to sleep, you might see an error message later such as “Failed to initialize.” To correct, just turn your SOTACAT off, and then repeat the steps from the beginning. To turn off your SOTACAT you not only need to unplug it, but also turn off the power switch (if it has one), and unplug the TRS-to-TRS 3.5MM adapter (if it has one).
  • Click the “Connect” button at the bottom of this page, and you will see a list of serial ports (COM ports) that are installed on your computer. The list for your computer will look different from this example.
  • Select the serial port from the list that is most likely to represent your SOTACAT. This may take some experimentation. In the picture above, it is obvious since only one choice is for “USB JTAG“, but your computer might have multiple possibilities. If you don’t see an appropriate option, it is likely you either have a charging-only USB cable, or your SOTACAT is not turned on.
  • Click the “Connect” button at the bottom of the serial port selector.
  • At this point your web browser will attempt to communicate with your SOTACAT module. You should see a new menu appear like this:
  • Click on the “Install SOTACAT” option.
  • At the “Confirm Installation” prompt, click on the “Install” button:

Error: Your current browser does not support installing SOTACAT firmware via USB. You must use Google Chrome, Microsoft Edge, or Opera. Error: You must connect to this web page with secure HTTPS (and not your current insecure HTTP connection) in order to install SOTACAT firmware. Change your browser URL and try again.

Configuration after firmware installation

  • Turn on your SOTACAT: if your SOTACAT doesn’t have a switch, then plug in the TRS-to-TRS 3.5mm adapter.
  • On your cell phone connect to your SOTACAT’s WiFi hotspot. It will have an SSID in the form of “SOTACAT-xxxx” and an initial password of “12345678”
  • Open a web browser on your cell phone and navigate to the URL “sotacat.local” (iOS, MacOS, and Windows) or to “” (Android, or if “sotacat.local” fails). Note: do not use HTTPS, SOTACAT only supports HTTP connections.
  • Once the web page appears, click on the “Settings” button at the bottom of the page.
  • You will see a form with three pairs of WiFi SSID’s and Passwords. When the SOTACAT boots it will try and connect to these in order:
    • Client 1 – Normally this would be configured with your home network SSID and password
    • Client 2 – Normally this would be configured with your cell-phone’s “hotspot” SSID and password (especially useful for Android because it doesn’t always support the split networking needed to connect to both the SOTACAT WiFi at the same time as using the cellular network for getting SOTA Watch and POTA.APP spots data). On iOS devices you might not need to set this.
    • Server – in the field when the SOTACAT can’t connect to Client 1 or Client 2, it will advertise itself as a WiFi hotspot server using this SSID and password. This is the very SSID you connected to in order to see the initial factory default settings. Here you can change the default settings. In the field on an iOS device this hotspot is what you will normally have your phone connect to. On Android you invert and have the SOTACAT connect to your Android phone’s hotspot using Client 2. Note that some Android phones might work with the iOS approach, while others wont.

Using with SOTAMAT

A SOTAMAT compatible with SOTACAT has not yet been released and is in development. There are SOTACAT-aware Beta versions of SOTAMAT available at: