In a world where increasing noise and QRM levels in residential areas are worse than ever, radio amateurs have to look for solutions. So, do, what the professionals do, and set up antennas on remote rural areas, and use the internet to distribute the received signals to the amateurs. Use WebSDR techniques.

  • Offering an alternative for radio amateurs with high local man-made noise levels
  • Supporting making QSO’s (short latency <0.5sec)
  • Supporting ham bands only and including CW segments
  • 24/7 available, reliable and predictable
  • Antenna radiation pattern matching transmitting antennas common on residential locations
  • Not intended to be a shortwave listening station or to provide the best possible reception


Why the choice for WebSDR?

  • it offers a 400msec well controlled low latency
  • supports a large number of users

Low consistent latency <500msec is essential for making QSO’s using a WebSDR!


This WebSDR uses a single broadband antenna for the 80m/60m/40m/30m/20m HAM radio bands. It is intended to give radio amateurs the possibility to receive a good signal on these band, in terms of QRM/Noise. It has not the intention to be the best receiving facility. Amateurs have to use their own transmitting antenna at their residential locations. It makes no sense receiving a lot of stations that are not able to hear you. So transmitting and receiving should be in balance.

Location selection

  • We live in The Netherlands, which is a small country in Europe, stuck between Belgium/France, Germany and the North see. It has about 17.5 million people in a flat pancake of about 150 km wide and 300 km long.
  • So, it is quite crowded. And not trivial to find rural areas which are quiet enough for proper HF-reception. We did a lot of measurements in the province of Limburg, and finally came to a location in the village of Maasbree. It provides a low level of man-made noise, measured by Koos (PA0KDF) with professional equipment and our self's with SDRPlay sdr's. We have 230V mains power and high speed internet available, and most of all the support of Wim, PH4RTM  (


The WebSDR project  has been started under the responsibility of  Jan, PA0SIM and Loek, PE0MJX.  Team members are Wim, PH4RTM (location & infrastructure), and Theo, PA3TEO (internet, security). This team works now also together to operate the WebSDR.


A quick overview of the set up is given. The active small broadband receiving antenna is a 1.69 m2 small loop with a broadband amplifier. From there we use a 100m coax cable to the shack. In the shack we have a 5 band passive filter which is feeding 5 receivers for the 5 bands. These receivers are connected to one computer. On the computer we run Debian, with WebSDR software of Pieter-Tjerk, PA3FWM, and specific intermediate software for the SDRplay receivers. Bas, ON5HB, helped us with the intermediate software (TNX Bas). More information about the WebSDR project of Pieter-Tjerk can be found on

Pieter-Tjerk (PA3FWM) is the developer of this WebSDR   concept.

Initial development was for the bands 80m, 60m, 40, 30m and 20m. Later in 2020 we also started to work on a 2m websdr, which came to life end of 2020. Early June 2021 we splitted the 2m band in a lower band (horizontal Big Wheel) and a upper band (vertical Diamond). Most of the work for the 2m band was copy and past, but a separate chapter is written to discuss specific 2m issues.

Short user manual

  • Browser, most important is using the best browser for this site, which is the Firefox
  • Preferred browser for WebSDR is Firefox or CATsync. See right column. But e.g. Microsoft Edge will also work.


  • Using the keyboard, memories, etc.

  • Frequency can be set by:

    1) Preset buttons

    2) Clicking/dragging/scroll wheel on frequency scale

    3)Direct input in frequency field

    4) Fine tuning in +/- 10Hz steps

    5) Keyboard shortcuts

    6) Band selection buttons

    7) Memories

    8) Click on memory labels in waterfall

    9) Bookmarks e.g.:

    10) CATSync and your own transceiver

  • Many possibilities, check the link in the right  column.


In CW mode the receiving frequency is the center frequency of the pass band.
The "BFO" frequency is indicated by a vertical line 750Hz higher. Lower side band CW is used.
750Hz is the default CW pitch.
By using the shift buttons the center of the pass band shifts and so the center frequency shifts.
However in effect the pitch frequency is changed.
The pitch frequency step is 31.25Hz. That is set by the digital signal processing (FFT) in the WebSDR.
When using the memories for CW these settings are also stored. Recalling a memory sets also the pitch.
Clicking on CW labels behaves differently. The present setting of the pitch(/shift) is maintained.
Unless the present setting is a SSB setting. The default 750Hz setting is then used.

Narrower CW filters with a bandwidth less than 300Hz have an increasing attenuation.
220Hz/240Hz  -1dB
180Hz/150Hz  -3dB
120Hz/90Hz  -6dB

For cw, the bandwidth must be set to >=750kHz for the squelch to work properly. The websdr now stores changed band pass settings for the duration of the session.


S-meter indication is set for an equivalent antenna factor AF=0.35 on all bands. Note: the antenna is not calibrated! Calculated numbers are used for the antenna. On 80m and 60m a full size dipole can give up to 6-12dB (1-2 S points) higher signal levels (both noise and signal).

One S-unit is 6dB according the IARU definition. On all commercial Japanese transceivers one S-unit is 3dB. Even on the IC-7300. This is done deliberately. The indication in dB over S9 however is mostly correct. Also the S-meter indication depends on the pre-amplifier settings. E.g. on the Yeasu transceivers the first pre-amp must be enabled for best S9 = -73dBm. 

The default setting for the WebSDR S-meter is 6dB per S-unit. If needed the 3dB per S-unit can be selected.
For signal levels S9 and higher the S-meter indications are equal for both settings.
Suppose a S9 signal drops 6dB. The S-meter indication drops to S8 using the 6dB setting and to S7 using the 3dB setting.

A consequence of the 3dB/S-unit, as on the Japanese transceivers, the S-meter reading drops below S0 on quiet bands.
On 30m and 20m for noise and weak signals the S-meter indication is below or at S0 even in SSB mode.
If Japanese transceivers would correct for pre-amplifier gain the S-meter indication would stay always below S0 for weak signals on quiet bands.
That is why the Japanese transceivers don’t correct for pre-amplifier gain.

The websdr S-meter is not a true RMS meter. For RMS noise level indication subtract 5 dB.


  • WiFi can be used for mobile devices, but the best result in terms of latency and/or hick ups is got by using hardwired internet connection.

  • During downloading of updates of Windows, audio hick-ups might occur.

Frequency tuning

The actual tuning frequency step is 31.25Hz for all modes on all bands. That is set by the digital signal processing (FFT) in the WebSDR. When setting the frequency in steps of 1Hz a carrier will change frequency each 31.25Hz. As a result the maximum frequency indication deviation from the actual tuned frequency will be 31.25/2=15.625Hz.

For SSB the scroll step with the mouse is set to 31.25Hz.

For CW it is set to 10Hz in order to ease setting the frequency as close as possible to zero beat

CATSync and VSPE

  • CATSync is a little program, which can be bought online for 10 euro. It is more or less a browser, with special functionality for WebSDR. It works OK with e.g. a FT-950 and FTDX5000, and it should work with many other sets, because it uses Omnirig.
  • VSPE is a com port splitter which can be used in combination with CATSync.
  • Using CATsync and VSPE combined with other apps e.g. Logger32, UCX or N1MM is not trivial. All these apps act like the captain on a ship (which is your set), and the protocols are not the same. There are two concepts, one is using CATSync as the Captain app, and connect other apps to CATSync. We do not know of any implementation of this yet. If you know, please let us know. The other concept is writing a program (e.g. in VB) as the Captain, and interface this smartly with all the apps. Using the VSPE app can be helpful because of the possibility of all kinds of combining COM-ports. We are working on an implementation of this. If you know apps who do this please let us know.
  • I have a VB program now up and running, which captures TX/RX info from a VSPE channel, and mutes the audio in the PC while in TX mode. This is for not hearing yourself on the websdr (delayed) if you are talking or cw, which is very confusing. Also the program picks up the frequency from the channel and sends it to the app UCXlog, I can log directly with the correct frequency, and still work on contests with i.e. automatic TX.
  • It also works with Log4OM
  • If you like to implement CATSync with VSPE , and other programs, more details can be found in CATSync.
  • CATSync is using Omnirig to talk to the different transceivers. Beware of the fact that in Omnirig we found several bugs in the ini files of the FT-950 and others from Yeasu. In the FAQ we describe the details of the bugs we found and solved with the help of Oscar (DJ0MY), the creator of CATSync.


  • If you would like to contact us for information or suggestions please mail to websdr-maasbree at
  • This project is a hobby project and do not expect professional services or an answer. We only answer e-mail if we think it helps the WebSDR project.


    • The FAQ page is here FAQs


  • This WebSDR is set up by volunteers, radio amateurs, who want to enable the ham radio hobby for all ham radio friends who are suffering high man-made noise levels and extensive QRM.
  • This WebSDR has of course development and maintenance costs but we also have to pay the bill for 24/7 up electricity.
  • Donations, small or big, are always welcome to keep the site in the air.
  • For donations contact the sysops (websdr-maasbree at
  • Currently the list of donations is:
    • Jan, PA0SIM: Several receivers  (FIFI, SDRPLAY's, filter, cables, antenna)
    • Loek, PE0MJX: Several receivers (SDRPLAY's, Coax cable, APC, cables,                                                            network switch)
    • Wim, PH4-RTM: Antenna Location, shack, power, internet
    • Wim,PE1WVD: Laptop
    • Anonymous Dutch contributor: 50 Euro
    • Anonymous UK contributor: 22 Euro (for the electric bill !)
    • Veron department A31 contributes 1/3 of the electricity bill
    • A. A. Aaltsz: 25 euro (for the electric bill)
    • Hr van der Linden: 100 euro
    • Many other anonymous contributors

Add comment


Loek Veeger
5 months ago

For all who use this websdr:
We installed a horizontal Big Wheel antenna on the lower 1MHz of the 2m band.
The upper 1MHz has still a vertical Diamond.
Comments on the working of the Big Wheel are very welcome.

Florian Kröning DO2BX
a year ago

Thanks for that fabulous Websdr. Its greatful

a year ago

schijnbaar is de url gewijzigd.
Probeer eens "" .
73, Bart

a year ago

Hallo Maasbree ,

Een vraagje , ik luister met regelmaat naar Web SDR Maasbree - vanuit Maastricht.

Helaas doet de link het niet meer om de ontvanger te beluisteren. Mogelijk is er een storing ?

Groetjes , John

gerard pd0pkg
a year ago

Dit ziet er heel mooi uit ,vind alleen jammer dat alles in het engels is maar alles werkt perfect
mijn complimenten

Loek Veeger PE0MJX
a year ago

May 7, this is the day,.....we finally have access to fast internet via the glass fiber cable !!
We updated the connection parameters, and started to operate the WebSDR in a test with over 20 users,......lets see what happens the coming days,.....
It looks promising,

Loek Veeger
2 years ago

The broad band internet connection with fiber cable is still not yet available. The last planning given by the company is that in May the connection should be ready and available.
We all hope that Corona is not delaying the planning again,......

Loek Veeger, PE0MJX
2 years ago

Nice initiative. Gives local amateurs back their hobby.