Identifying Signal Types

There are two ways to tell what type of signal you are encountering. You can view it's pattern on the waterfall or you can hear it. We will take a look at 3 of the more common signal types here. Links at the end can get you started in identifying other signals as well.

Signals on the waterfall vary in brightness or vivid color, as mentioned previously. The stronger or brighter the color, the stronger the signal. Digital data may seem quite solid. But so can voice. Morse Code is easy to pick out as it shows sporatic signal bursts. However, beacons beep or burst at a steady, predictable rate.

Digital Data

Digital data include fax, teletype (PSK, BPSK, etc.), SSTV images and other data packets.

Morse Code

Also called CW (Continuous Wave). This is the patterned beeps that stand for letters or numbers.

Beacons and Channel Markers

Beacons can be used to hone in on a signal or location (such as in the case of ships signaling for help). Channel markers are constant signals that keep sound in the frequency to discourage others from using that frequency. Sometimes they are pulsed noises but also could be continuous sounds that might be mistaken for a data packet.

Time Sync

What may sound like a beacon or channel marker might also be a time sync channel such as the United States National Institute of Standards and Technology (NIST) transmitted from Fort Collins, Co. (call sign: WWV). This is usually a tone or chime and click every second which looks a lot like a channel marker on the waterfall, followed by voice announcements of the time (and occasionally other information). If you listen to it for awhile, eventually you'll hear someone announce the time (in UTC). For more info on this channel, please see the Freqs Page.

Voice or Music

Voice and Music signals are more dense. Here is an example of a voice signal:

Another way to determine the type of signal is simply by listening to it. Here are some examples:

For more sound examples, see the Digital Modes Samples web site

Knowing what type of signal you are dealing with will also help you in determining what type of decoder method to use. But be careful to not decode private information!


You can also tell if there's interference from lightning storms across frequencies. DIY Lightning Detection with SDR shows some of the things to watch for on the waterfall. If you want to home in on storms, first look for the storms using the Lightning and Thunderstorms Map. Once you find where the storms are, find an SDR in or near that area and see if they are online. Tune in and see if you can spot the interference across the frequencies.