How to setup a webSDR as your secundary receiver

Manmade QRM; I am now an expert by experience. In the almost 17 years that I have lived on my current QTH, I have seen the noise floor on 20 meter band, rise from S1-S2 to an average S5. I did manage to significantly reduce the interference from the largest QRM sources here, such as the micro inverters of my neighbors’ solar panel systems. Still, a lot of disturbance remains. Phone chargers, adapters, LED lamps, fan and A/C motors, etc. Impossible to tackle all those sources in a densely populated area like mine.

Help of a receiver elsewhere

So sometimes I need the help of a receiver elsewhere for listening on HF. Fortunately, there are quite a few SDR receivers that can be listened to via the worldwide web, while the number of webSDRs is still increasing. There are good and less good receivers among all those webSDRs. I think that many amateurs and SWLs agree with me, that the webSDR at the University of Twente in The Netherlands has an exceptionally good reception on HF.

The Twente webSDR is considerably “quieter”

Compared to at home on the 20 meter band, the Twente webSDR is considerably “quieter”. The university receiver sometimes performs up to three S-points better than my Kenwood TS-480 and my 13 meter long elevated vertical with remote auto tuner. This exceptionally good reception has a lot to do with the special arrangement of the antenna, a Miniwhip, about which PA3FWM wrote in this article.

Helpful if the webSDR automatically synchronizes frequency

So now and then I turn to the Twente webSDR. For example, I have already made a QSO on various bands while I also listened to the webSDR online. That goes quite smoothly. Rather a challenge is that you have to change the tuning of the webSDR every time you change the tuning of the transceiver. It would be helpful if the frequency of the webSDR automatically synchronizes with that of the transceiver. Talked to other amateurs years ago how useful that would be, but it never got beyond an idea.

This application did exactly what I was looking for

Because of Covid-19, I spent more time in the shack to experiment with propagation on 60 meter band. Because I sometimes had to use a webSDR for reception, the need to synchronize it with the transceiver became topical again. By coincidence I came across a website about the CATSync program. This application did exactly what I was looking for. I hadn’t seen it before, so I decided to give it a try.

Stripped-down web browser based on Chrome

CATSync is developed by DJ0MY Oscar Diez. The Windows program is actually a stripped-down web browser based on Chrome. It uses OmniRig (freeware at to communicate with your transceiver via CAT. Javascript is used to synchronize the actions on your transceiver, VFO and mode switch, with the webSDR server. For example, the frequency and mode of the webSDR are neatly synchronized with that of your transceiver. But also the other way around. If you click on a frequency in the waterfall of the webSDR, your transceiver synchronizes. Actually, this also creates a kind of ‘remote’ panadapter.

CATSync at work using the Twente webSDR, synchronized with the Kenwood TS-480

The user interface has been well thought out

I have been using CATSync (version 1.21) for a month now. The application runs flawlessly on my PC running Windows 10 Professional, with Intel Core i5 processor and 8 GB RAM. It also runs on my nine-year-old Asus Netbook with Windows 7 Home, with Intel Atom processor and 2 GB RAM. The user interface, unlike other radio amateur applications, has been well thought out, just by keeping it simple. You immediately find your way without a manual. You paste the URL (web address) of the webSDR in the address bar. The webSDR synchronizes with the transceiver within a fraction of a second. The delay between turning the tuning knob on the transceiver and the webSDR is minimal. You can also create a list within CATSync with your favorite webSDRs.

My favorite webSDRs stored in CATSync

Helpful as a tool to check out propagation

I have tested CATSync on various webSDRs, which can be found at and at What is immediately noticeable is the sometimes considerable delay in the audio. This varies from half a second with the webSDRs running on the PA3FWM software, to three seconds with many KiwiSDRs. Certainly at three seconds you can no longer use webSDR as support for a QSO. However, you can use a KiwiSDR very well to see if you can hear yourself anywhere in the world. Very helpful as a tool to check out propagation on your favorite band. I am very happy with CATSync. It does exactly what it promises and I can recommended it if you use webSDRs frequently.


Multiple programs using one serial port

The only thing is that the application continuously uses the transceiver CAT connection via the serial port of your computer. So how to use any other program besides CATSync like HamRadio Deluxe, N1MM or WSJT-X? Fortunately, there are programs that make it possible to split the serial port. With the freeware application Virtual Serial Port Emulator from, you can use the Splitter function to turn your physical serial port into a new virtual splittable serial port with which all programs can use at the same time. The LPB2 program (thanks to PG7M for the tip) is even more extensive, where you can assign specific virtual COM ports to a program.

Phyisical port COM 1 now in use as virtual COM 5 which allows multiple programs to hook up with your transceiver.

Purchase and download

CATSync is not freeware. But you have a very useful app for just € 9.95 (July 2020). For more information or purchase, visit the CATSync website.

This article was also published in Dutch in Electron magazine September 2020.