WebSDR Introduction

A WebSDR is a Software-Defined Radio receiver connected to the internet, allowing many listeners to listen and tune it simultaneously. SDR technology makes it possible that all listeners tune independently, and thus listen to different signals; this is in contrast to the many classical receivers that are already available via the internet.

More background information is available here. Questions and comments can be sent to PA3FWM, the author of the WebSDR software and maintainer of this site; but please check the frequently asked questions first.

A complete list of all WebSDR servers can be found here:  http://www.websdr.org/
Different servers will cover different bands. There are servers all around the world. Many servers are experimental and may not be available at all times. Here are some servers that have worked well for me:

http://hackgreensdr.org:8901/  (England)
http://marcohaas.de/   (Germany}

The following screen grabs are from the KFS WebSDR HF radio receiver system located 6 miles south of Half Moon Bay, California; maintained by Craig, W6DRZ.

The purple box is called the ‘waterfall’ and provides a visual display of the radio activity over a slice of bandwidth. The data flows UP. Different types of radio transmissions have unique displays. The waterfall can be moved by clicking your mouse in the display and dragging it towards the frequency you want. You can also enter a specific frequency in the box at the lower left.

The current frequency being monitored is shown by the little ‘pyramid’ just below the waterfall. It can also be dragged with the mouse, but be careful to click in the middle of the pyramid. You can also change the bandwidth by clicking and dragging on the edges. The vertical line in the middle of the pyramid indicates the exact tuning point. In the above example an AM transmission is being monitored. The pyramid is very wide, and the tuning point is the middle of the signal.

Sideband signals are tricky to tune:

The receiver is tuned to a LSB signal on 3937 kHz. 40, 80, and 160 meters are usually LSB, other bands USB. Sideband signals are tuned to the EDGE of the signal display. You may need to make fine adjustments to make the speech intelligible. Note that the tuning pyramid is much narrower than the AM signal. You can zoom in on a frequency using the buttons on the lower right to make things easier to tune.

CW (morse code) signals are very narrow bandwidth:



This signal is in the CW section of the 40 meter band. The waterfall has been zoomed in. The tuning pyramid is very narrow to capture a single CW signal.

There are many different kinds of digital signals to be found in the amateur bands, too. Each digital protocol has a unique display on the waterfall.

Feel free to experiment! You can’t hurt anything. If things quit working, just refresh your browser and start over.