I don't hear any sound. How come?
Besides obvious problems like your computer's sound being muted,
one possible cause is that your web browser does not support this.
There are two entirely different techniques used to play the sound.
Your computer has to support (at least) one of them for sound to work:
- Most used nowadays: HTML5 WebAudio, since this has been available
in most web browsers since several years:
Unfortunately, Internet Explorer does not yet support this technology.
- Firefox version 17 or later
- Chrome version 10 or later
- Safari version 6 or later
- Opera version 15 or later
- Edge (as supplied with Windows 10)
- Essentially only for Internet Explorer, you can also use Java applets; for this, you need
not only a webbrowser, but also version 1.4.2 or newer of Java working on your computer.
to find out if you have Java and which version it is.
You may need to enable Java applets per site; see here.
Some WebSDR sites have disabled Java support; those sites can only be used with HTML5 WebAudio.
So, which one do you use?
WebSDR sites try to detect what your browser can do.
If HTML5 WebAudio is available, it will be used; otherwise, Java will be tried.
I'm using Chrome and don't hear audio (on some sites)!
Since version 71, Chrome does not allow every website to start playing audio,
in order to stop annoying advertisements.
Chrome tries to guess whether you want audio or not, but doesn't always get it right.
On some WebSDR sites, you'll get an "audio start" button, on some you don't.
If you don't get audio, try the following:
(thanks to K9GL for these instructions)
- At the top right, click the 4 vertical dots, and then Settings.
- At the bottom, click Advanced.
- Under "Privacy and security," click Site settings.
- Select "Sound"
- Select "Add" and enter "http://*"
Note that the above effectively disables Chrome's "autoplay" policy for
all http sites.
Although stopping automatic sound from advertisements is a noble idea,
I think Chrome's autoplay policy is fundamentally wrong. Instead of trying to guess what
the user wants, the browser should simply ask the user whether he/she wants to allow the
page to play sound (and remember that for later visits, of course).
Only some WebSDR sites work; on others I get no sound and no 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.?
Yes, if there is a browser for your device which supports HTML5 WebAudio.
On Android devices, these include Firefox, Chrome and Opera (but not Opera-Mini);
and even recent versions of Android's built-in browser should work.
On iPhones, iPads etc, you can use the built-in Safari browser,
but only if you have iOS version 6 or later.
I'm using an iPhone/iPad and don't hear audio!
An issue with iPad (-like) devices is that they have two mute switches:
one which affects music, youtube, etc., and one which affects system
sounds (like mail notification bleeps).
Somehow, iOS treats the WebSDR audio as the latter.
So please check that you haven't accidentally muted the system sounds.
On some devices this is a software switch, on others it's a physical hardware switch.
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
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?
Can I specify the frequency and mode in the URL when linking to a WebSDR ?
Yes, using the ?tune= parameter, like
to listen to 198 kHz in AM (BBC Radio 4).