CATSync operation

The idea:

You want to listen to websdr's but transmit with your own set. So, you want to make QSO's. The websdr should be in the neighborhood, but not at home, because you have a lot of QRM and man-made noise on your QTH.



There are a few challenges to get this done in a proper way:

- I need to connect my transceiver to my computer (CAT)  (If you do this with a serial interface, use FTDI USB-Serial

  convertors, and no Prolific, see FAQ).

- I need to use a browser which is specifically developed for websdr's, it is convenient for controlling the transceiver.

- I also want to do CW

- I don't want to hear the websdr when I am transmitting myself. This is very confusing, because of the latency of the websdr.

- The latency of the websdr should not be higher than, let's say 500ms. Otherwise a QSO can be confusing because of the latency.

- I want to use a log program to log my QSO's


Well, there are several ways to do this. I will explain a setup which is working very well in my shack for many months. And many people use it and confirm it.


We need a standard CAT interface between our PC/laptop and the transceiver. In my case I use a FT-950 transceiver. My PC is connected via the serial port of the transceiver and a USB port of my PC, using a 'serial to USB' stick (FTDI ! not Prolific). To let this work properly I also used several HF ferrite chokes to keep the HF energy from the cable. This depends heavily on your power and the quality of your antenna system. Keep the HF currents from the outside of the cable,......

I use port 10, set in the PC.

Captain on the ship:

We have to steer/control the transceiver with a program. There are several programs doing this. WSJT-x, Log4OM, UCX. They are developed for logging your QSO's directly in the computer, and also control a whole lot of parameters in the set (frequency, band, etc). It is important to understand that you need only ONE captain on the ship, meaning one program controlling the transceiver.


OMNIrig is a free little program that is more or less also a Captain. It communicates with the transceiver via a  CAT interface to the transceiver. Many programs can use the OMNIrig program to interface to the transceiver. But keep in mind, two programs using OMNIrig can only talk to the transceiver after each other. Of course,...... we have only one frequency to use at a time,....etc.


Well, CATSync is a 10 euro costing app, which can also act as a captain on the ship. It is a modified (Chrome based) browser, that is adapted to work specifically with websdr's. That is what we are going to use ! The point here is that CATSync uses OMNIrig. Meaning that other programs using OMINIrig should also work with the transceiver.

In my shack I use for example CATSync and LOG4OM, and this works fine. LOG4OM follows the frequencies, band info, mode etc.

To let this work you go to the settings of LOG4OM, than to Configuration and CAT interface. Chose OMINIrig as your CAT engine.

CATSync is using OMINIrig by default.

But there are other ways to work with CATSync in combination with other programs , not using OMINIrig. See further discussion


VSPE is a little program, which can be used for free and is developed to create virtual ports, port splitters, etc. This program is used  to create my own setup.

Visual Basic program:

We are going to write a small VB program to make sure we can do what we want, and not confusing the CAT interface by using more than one Captain at a time.


So concluding we have the following setup:

Well, my transceiver is a FT-950 with a serial interface. I bought a serial to USB convertor and installed the little device between the transceiver and the PC.

Let's look at all the little blocks in the PC.

CATSync: buy the program on line, install it, and set the port on 15. Find a websdr ( and open it.

OMNIrig: get the little program on the net and install it. Very easy to do.

I use Log4OM to log my voice QSO's. Get the program, install it and put the interface on port 15.

UCX: I use UCX to log my CW QSO's. Install it, put the interface port on 16 ! I will explain later.

VB-program: The program will be provided, but for now, it should be installed in windows.

VSPE: get the program, install it, and set up a splitter (4 x port 15 to 1x port 10), and a pair (port 16-17). It should look like:


OK, what is the program doing.

- The program starts with opening port 15 and 17

- The program is looking at the data stream on port 15. Just looking,....

- There is a lot of communication going on between the OMNIrig program and the transceiver. We have to pick the command about the frequency. We have to do some smart filtering to make sure the command is from the transceiver and corresponding to the frequency. If we get the frequency, we send the frequency to the port 17. 17 is connected to 16 by VSPE, so UCX is picking up the frequency.The yellow field in UCX is going to turn into white, and shows the frequency of the transceiver. That's all for UCX. UCX is trying to control the set by giving a lot of commands over port 16/17, but the VB-program ignores it all. So, UCX is not the Captain on the ship, it is just listening to freq-commands coming from the VB-program.

It works 100%. If you log your QSO, you have the correct frequency in the log.

- The program is also filtering the commands from the transceiver, which are corresponding with TX and RX. We are going to filter out these commands and use it to set the audio on "ON" (RX) and "MUTE" (TX). So, if we are transmitting, and talking or giving CW, we do not hear us back in the websdr audio !

- Because the websdr has latency (few 100 milliseconds), the audio is set to 100% again after this few 100 milliseconds. Otherwise you will hear yourself back in the websdr the last few 100 milliseconds). This delay can also be configured in some transceivers. My FT-950 can do that. Make sure the delay of the transceiver and the software together are not to much (more than 500ms) otherwise you miss the start of the transmission of your QSO buddy.

- For this controlling of the PC's audio, we use a little free program, which is called "nircmd". Get the program and put it in the folder c:/nircmd. In the folder you should see at least the program "nircmd.exe". That is the one we are going to invoke in the VB-program. Basically it is a command line program, with a ship load of very nice little functions. 

We are invoking the nircmd program with the options "MUTE" and "set100%". You can see what the program is doing if you open the Volume mixer (windows, right button on the taskbar).


This is it, folks. Have fun !


PS Later versions of CATSync have implemented the mute function in the program. That's fine, we don't the mute function in the program no more. The code can be skipped or commented out.



Muting Program Source In Vb
Plain text – 7,3 KB 374 downloads

To process this file, I did the following. I have installed Microsoft Visual Studio 2017. I opened a new project, pick the "Console App" .

A start file is opening. Get rid of the complete content and paste the VB source code Muting Program Source In VB. Give it a clear name. Build the file and Publish it to a folder in your PC. From there install it in your PC.

Open the volume mixer and look at the volume bar. If you engage your PTT, you see the volume goes to zero.


If you want to make QSO's, put on your set, start your VSPE-program, start CATSync, start your VB-program, start your logging program. Make sure VSPE is running before you start other programs, because they need the ports.


Need any help ? give me an e-mail.  "".


For the VSPE program look here.

For the nircmd program look here.

For the CATSync program look here.

For the Ominirig program look here.

For the UCX program look here.

For the LOG4OM program look here.