SDR Sunday – monitor web SDRs and decode digital data

Want to try out software defined radio (SDR) before you buy or build a rig? Or do you just want to see what all the ham radio chatters about? Then check out the online SDRs available for your listening pleasure at WebSDR. This unique website lists dozens of online radios which you can click on to monitor signals on various amateur radio bands as received at locations around the world.

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.

You can read more about this outstanding project by following the background information link on their webpage.

WebSDR provides great potential for RF experimentation and research by both radio hobbyists and licensed radio amateur alike. If you don’t have an HF receiver, or you live in an area where you can’t install a decent antenna, this site will open up endless possibilities to listen to various modes and learn about radio signal propagation. You can either listen to voice transmissions or try your hand at demodulating digital modes. (More on the digital modes later.)

Each station available on WebSDR has a user interface which gives you individual control over various receiver parameters in real time. You can select the type of visual representation of the band (i.e., waterfall), change the frequency, bandwidth and mode.

SWLs and non licensed hobbyists can listen to ongoing amateur radio operations without having to buy an expensive receiver.

For licensed amateur radio operators the potential uses are HUGE. Hams can use this site’s resources to check out signal propagation conditions, contest or net activity, and more. Most significantly, ops can check out the quality of their own transmitted signals as heard on SDRs located in various parts of the world! Is anyone in Europe hearing my CQ on 14.250 MHz? Is my PSK31 signal REALLY clean? Well, just tune a WebSDR to your frequency, transmit and find out!

Now for the digital stuff:
If WebSDR provided a plug in to decode digital transmission, what fun would that be? You have to work to achieve results, and when newbies learn the same with this online resource as they would with a physical shortwave radio the learning process if more meaningful.

So what program do you need to decode the digital transmissions? One excellent choice is the open source interface known as FLDIGI. FLDIGI is a digital modem program for Linux, Free-BSD, OS X, Windows XP, W2K, and Vista by amateur radio operator W1HKJ, and it’s an amazing example of an open source project.

For the purposes of using FLDIGI with WebSDR, you will only need to download and install the FLDIGI files: the supplemental download files such as Flmsg and Flrig are only needed for installations involving a transmitter. You’ll definitely want to check out the Begineer’s Guide for an overview of the many features this program offers.

Once installed, fire up FLDIGI and follow the directions to set up your soundcard as the audio input AND output device. Now comes the “deep tech” part: take an audio patch cord (shorter the better) and connect your soundcard’s audio out to the audio in! Now when you locate a digital signal on WebSDR, you run FLDIGI, plug in your patch cord and begin decoding. Note that you will have to first tune the desired signal on WebSDR, then in the FLDIGI window you must tune to the desired signal on that waterfall as well.

We hope you find these resources interesting. They are an excellent example of free online and open source technology coming together to help everyone learn by exploring the RF. The only hardware you need is an audio patch cord. But be warned: monitoring WebSDR can be addictive.

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