Frequently Asked Questions about the WebSDR project

Using the WebSDR (the client-side)

I don't hear any sound and don't see any waterfall displays. How come?

You need JAVA working on your computer, with version 1.4.2 or newer. Try http://javatester.org/version.html to find out if you have Java and which version it is.

Can I use the WebSDR on a smartphone/tablet/etc.?

Unfortunately, the web browsers on these devices do not support Java applets, which are essential for the WebSDR to work. Recently, I've started creating an alternative for the Java applets, using some very new extensions to HTML5. This now seems to work on some iPhones and iPads (running iOS 6), and some Android devices (using Firefox). This is still work in progress, so I have good hope it will work on many more smartphones and tablets in the future. The experiments can be tried at http://websdr.ewi.utwente.nl:8901/.

How can I decode digital signals like PSK31, RTTY, etc.?

You need to feed the received audio from the WebSDR web page to a separate program that can decode these signals. This can be done as easily as by putting a microphone in front of the computer's loudspeaker, or by using software such as Virtual Audio Cable on Windows. See for example http://www.oz9aec.net/index.php/component/content/article/63-sdr/290-fun-with-websdr-and-fldigi and http://www.hamradioandvision.com/websdr-digital-modes/.

Can I decode DRM ("digital radio mondiale") signals?

No. These signals are 9 or 10 kHz wide, which is much more than the bandwidth streamed from the WebSDR server to the clients. Furthermore, I think most DRM programmes can also be heard directly on the broadcaster's website.

Running a WebSDR server

Where can I download the server software?

Nowhere. However, I distribute it (without cost) via e-mail to people who are setting up a publicly accessible server (i.e., listed on websdr.org), and who have everything needed to set it up: a soundcard-based SDR, a computer running Linux, and a fast internet uplink. If you have all of these and are seriously interested in setting up a server, email me with some details about your plans and equipment.

Does it make sense that I set up a WebSDR server?

Have a look at the current list of servers on http://websdr.org, and judge whether your server would add something to that, e.g. by being in an unusual location, having a special frequency range or a very good antenna site. Yet another 40 m WebSDR with a dipole in western Europe is probably not useful, but one on Antarctica would be quite nice...

My SDR is an XYZ. Is it supported by the WebSDR server software?

Many amateur SDRs are quadrature mixers which downconvert radio signals to the audio range and feed this to the computer's soundcard. This category includes the well-known Softrock kits, and very many similar schematics and designs on the internet. Also the FunCubeDongle is included. This category of SDRs is supported.
If the SDR has some kind of synthesizer or other configuration settings, the WebSDR software will not take care of this. You'll have to use other software to configure it.
Other SDRs typically use a fast A/D converter and digital hardware to filter part of the spectrum; they are typically connected to the PC via USB or ethernet. Unfortunately, there is no standardization among the interfaces for these SDRs, which makes it hard for me to support them. I'm considering adding a generic interface for them though, but for now they cannot be used.
The (in)famous RTL-SDR dongles (cheap VHF/UHF SDRs) are now supported, but only on VHF/UHF, not with upconverters. Note that these SDRs have a rather small dynamic range, so should only be used in situations where there are no very strong signals.

What Linux distribution should I use for the server?

That does not matter much, as long as it runs on Intel (compatible) processor, either 32 or 64 bits. Many WebSDR servers run on Ubuntu; I myself usually use Debian.

What soundcard should I use for the server?

Start with any that you happen to have and is supported by your Linux distribution. I can't advice you on more advanced sound cards. Don't overlook the motherboard's on-board card: modern motherboards often have surprisingly nice cards, with e.g. 4 channels at 192 kHz samplerate.

How much internet uplink bandwidth does a WebSDR server need?

Obviously, this depends on how many simultaneous users there are. Furthermore, it depends on how many waterfall displays each user has (i.e., how many bands), and the scroll speed of those waterfalls. With a single waterfall at "slow" speed, count on about 100 kbit/s per user.

Can I run the server on the Raspberry Pi or another ARM processor?

Yes, the package now also contains a binary for the RPi. However, the RPi's computational power is limited, so it can't handle more that 96 or perhaps 192 kHz of radio bandwidth.

What is the most recent version of the server software?

The latest distributed version is 10a. If you have an earlier version, and have not been sent the 10a version, then most likely your WebSDR was not running publicly around the time I distributed the 10a version.

Is the hardware being used at the 29 MHz wide WebSDR (running at the University of Twente) available for sale or duplication?

No. This is a rather experimental board; it's not a commercial product, and it is not well enough documented for easy duplication. Also the special WebSDR version running it is not ready for distribution.

Never asked questions (unfortunately)