Frequently Asked Questions about the WebSDR project

Using the WebSDR (the client-side)

I don't hear any sound. How come?
Nowadays, there are two entirely different techiques used to play the sound. Your computer has to support (at least) one of them for sound to work:

So, which one do you use? Most WebSDR sites now support both, and they offer, just above the waterfall display, controls where you can choose which one to use, separately for audio and waterfall. The site tries to make the best guess: if your browser supports HTML5 WebAudio it will be used; otherwise, it will choose Java.

Only some WebSDR sites work; on others I get no sound or waterfall.
Please have a closer look at which sites work and which don't. Is it such that only those on "unusual" ports (i.e., those that have a number like :8901 in their URL) work, while those without a port number (those run on the default web server port 80) don't work? Or the other way around?

If only those on port 80 work, you're probably behind a firewall that only allows port 80 (and a few others). This is often the case in public WiFi networks and office networks.

If only those on ports other than 80 work, you're probably behind a web proxy server, which doesn't know how to handle the (non-standard) audio and waterfall data streams. The proxy server may also be in your internet service provider's network.

Can I use the WebSDR on a smartphone/tablet/etc.?
That depends. Unfortunately, the web browsers on these devices do not support Java applets. However, nowadays most WebSDR sites do support HTML5 WebAudio, and those can be used on smartphones.

On Android devices, you can access these using the Firefox browser; Chrome and Opera may also work, and it seems in the latest Android update (4.4), even the built-in browser supports this.

On iPhones, iPads etc, you can use the built-in Safari browser, but only if you have iOS version 6 or later.

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.
Decoding them serverside is not an option either, because of the CPU load for the server.
Furthermore, I think most DRM programmes can also be heard directly on the broadcaster's website, so there is not much reason for listening to them via a WebSDR receiver.
I get a warning that the WebSDR Java applets are "unsigned". What does that mean?
See here.

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: what kind of SDR hardware, what kind of internet connection and computer, what frequency band(s), and what does that add to the current offering on websdr.org (see the next question) ?
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. A generic interface for them is being added, but for now they cannot be used.

The (in)famous RTL-SDR dongles (cheap VHF/UHF SDRs) are now supported. Note that these SDRs have a rather small dynamic range, so should only be used in situations where there are no very strong signals. If you want to use these, please check carefully that they are not being overloaded, e.g. by comparing their reception (using normal SDR software) to e.g. a normal non-SDR receiver; in particular, pay attention to weak signals: they should not disappear into the noise.

My SDR can be tuned from 1 to 1900 MHz. Can I offer all of that tuning range to the users?
No. Such an SDR does not feed the entire 1 to 1900 MHz spectrum to your computer: that would be way too much data. Instead, a small part (perhaps 1 or a few MHz) are filtered out in external hardware, centered around some frequency that you can tune. With the WebSDR software, users can only tune around within that small part of the spectrum. You (as the operator of the site) choose the centerfrequency.
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.
Do I need to install Apache, PHP, MySQL etc.?
No, the WebSDR program is self-contained, containing both the radio signal processing and a small webserver.
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 send the raw data from the SDR to another site where I have more internet uplink bandwidth, and run the server there?
Although it might be possible in theory, it typically doesn't help, because that raw data stream is much bigger than the data going to the users. For example, a 96 kHz wide SDR already needs about 3 Mbit/s for the raw stream (namely, 96000 (samples/sec) x 16 (bits/sample) x 2 (I and Q channel)).
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.
Note that this means that the RPi cannot be used with the RTL-SDR dongles, because those have a much larger bandwidth.
What is the most recent version of the server software?
The latest distributed version is 11. If you have an earlier version, and have not been sent the 11 version, then most likely your WebSDR was not running publicly around the time I distributed the 11 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)

Can I use a WebSDR chatbox to repeatedly advertise my own homepage or youtube movie? Use foul language? Discuss xxx rated topics?
No, that is not what these chatboxes are meant for.
Can I put a list of links to WebSDR servers on my own website?
You can, of course, but it is a waste of effort. Your list will quickly become outdated as servers come and go and change their frequency range or internet address. In contrast, the list on http://websdr.org is updated automatically, so it is much more practical to link to this site.
Can I include someone's WebSDR site in a frame on my website, so that it looks as if this WebSDR is mine?
Let me reply with a question: do you feel doing this is fair?
When I notice people doing this with one of my sites, I take action against it.
I sent you a mail an hour ago and I don't have an answer yet. Should I resend it? Or better, spam it to all your e-mail addresses?
No, please don't. The WebSDR project is only a hobby project for me, and I get quite a lot of mail about it; it may take a couple of days for me to respond, as other things have higher priority. Only resend the mail if you got a bounce message.

If your question is not answered here, e-mail pa3fwm@websdr.org.