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URL parameters

What are "URL parameters"

In the address bar - typically at the top of a browser - is the URL which usually looks something like this: .  The main job of this is to tell the browser "where to go" to find the web page, but it can also be used to convey information to the web server.  

It's possible to use this to "pre-configure" the WebSDR so that when it gets loaded on your computer, it's already set up to do something - such as tune to a frequency and mode - but other things are possible, too.

Pre-tune frequency and mode:

All WebSDRs have the ability to set the frequency and mode in the URL and that is done as follows:

http://<websdr_address>?tune=[freq kHz][mode]

As an example:

The URL for WebSDR #1 of the Northern Utah WebSDR is:

Examining this, we see the host name ("") and the port number ("8901").  Most WebSDRs use port 8901 - but you'll see variations:  The Northern Utah WebSDR's different WebSDR servers (#'s 1-5, for example) use ports 8901-8905.  The final portion, "/index1a.html" specifies the web page on the WebSDR that has the user interface and for most Northern Utah WebSDR servers this file name is "index1a.html".

Knowing this, we will add the frequency and mode - and for this let's presume that we wish to tune to 7200 kHz using LSB, so we will use:

 For example, let's say that we want to listen to 14300 kHz using USB:  Since the Northern Utah WebSDR's server #1 covers only up through 40 meters, we would use Server #2, instead, so the URL would be:

Of course, one must make sure that the frequency that you specify is actually covered by the WebSDR that you plan to use:  If you specify a frequency that is not covered, you simply won't end up there.  As you can see, the example above goes to WebSDR #2 and the port number (8902) is changed as well to match.

The options for mode are:  USB, LSB, CW, AM, FM.  The Northern Utah WebSDR receivers also have SAM-U and SAM-L (upper and lower sideband synchronous AM, respectively.)

Other URL parameters:

only parameters that most WebSDRs support are the frequency and mode, but a number of additional parameters have been added to the Northern Utah WebSDR servers and a few others (e.g. KFS and the Maui WebSDRs) and these are described below:

This parameter is most useful for VHF/UHF FM  receivers where the no-signal S-meter reading is  pretty constant, and this value is typically set about 6 dB higher than that resting value of the the background noise (e.g. no signal).  Because of the varying signal levels and static crashes common on HF, it is likely to be less useful there.
The "Alt AGC" was implemented because the normal AGC does not work well for AM reception, the result being clicking and noise bursts on signals that are fading rapidly and/or appearing/disappearing when other key/unkey.  The "ALT AGC" was intended for AM only with its constant carrier and is not recommended for SSB use.
This may be necessary if you are running the CatSync software which does not seem to be able to deal with the "extra" digit representing 1 Hz.

Examples: - Tune WebSDR #1 to 3900 kHz, LSB - Tune WebSDR #4 to 7200 kHz LSB with 10 Hz display resolution for compatibility with "CatSync" - Tune WebSDR #5 to 14155 kHz AM with the S-meter squelch set to -80, alternate AGC and 10 Hz display resolution

New features/parameters are occasionally added, and when the are, they will be documented on this page.

Additional information:

Go to the Northern Utah WebSDR landing page