Learn / Guide 3

How to use a WebSDR

A step-by-step guide to KiwiSDR, OpenWebRX and classic WebSDR: tuning, modes, filters, zoom and the etiquette of using someone else's radio.

beginner 6 min read

Before opening the first one

A WebSDR is a real receiver, in a house or a club, that the owner connected to the internet. The page you open is its panel. Everything you hear comes from the antenna there, with the propagation and noise from there.

The three most common types have different panels, but the same four decisions: frequency, mode, filter bandwidth, and zoom.

KiwiSDR

1. Open the public list at kiwisdr.com/public. It is also available as a map. Each line shows the location, antenna, and how many slots are free.
2. Click on a receiver. Each one only accepts a few people at the same time. If it is full, choose another.
3. Type the frequency in kHz in the box and press Enter. For 7.074 MHz, type 7074.
4. Choose the mode using the buttons: AM, LSB, USB, CW, NBFM.
5. A colored band appears on the frequency ruler: this is the filter. Drag the edges to narrow or widen it.
6. Use the mouse wheel over the waterfall display to zoom. Clicking on a signal tunes to it. The guide How to read the waterfall display helps to know what each spot is.

If the waterfall display is completely dark or completely bright, adjust the minimum and maximum controls in the waterfall tab, or use the auto adjust button. The background should be dark blue, with signals popping out above it.

The extensions menu holds decoders running directly on the receiver: FT8, WSPR, facsimile, telegraphy, and others. They are the easiest way to see a digital mode turn into text without installing anything.

OpenWebRX

1. Look for a receiver on Receiverbook, which lists by map and by band.
2. An OpenWebRX does not show the entire spectrum. It shows a slice, the size that the equipment can sample. The owner creates profiles (40 meters, 2 meters, airband) and you pick one from the list on the panel.
3. Click on the waterfall display to tune and choose the mode: FM, AM, LSB, USB, CW. Depending on the receiver, there are buttons for digital modes like DMR, FT8 and APRS.
4. The squelch cuts out the hiss between transmissions in FM. Turn up the control until the noise disappears.
5. Mouse wheel to zoom, filter edges to drag.

One precaution: on many OpenWebRX stations, changing the profile changes the band for everyone connected to that equipment. If there are other people listening, think before changing.

Classic WebSDR

1. The list is at websdr.org. The best known is the University of Twente in the Netherlands, which covers 0 to 29 MHz and accepts hundreds of users.
2. Several WebSDRs cover only some amateur radio bands. Choose the band using the buttons.
3. Type the frequency in kHz or click on the waterfall display.
4. Modes are on buttons: CW, LSB, USB, AM, FM.
5. The filter is adjusted by dragging the edges of the yellow marker under the waterfall display, or using the narrower and wider buttons.
6. In current browsers, sound only starts after you click the audio start button.

Which mode to use

The division between LSB and USB is just convention, but everyone follows it. Digital modes like FT8 use USB on any band.

Tune in correctly in SSB

In AM and FM, being close is enough. In SSB, 50 Hz makes a difference. Off the mark, the voice sounds like a duck or a robot. Go by 10 Hz steps until it sounds natural. If it does not sound natural at all, you are on the wrong sideband: switch from LSB to USB.

In telegraphy, narrow the filter until only one signal remains. If two signals fight inside the filter, move the tuning to leave the unwanted one out, instead of just lowering the volume.

A wider filter gives a fuller sound and more noise. A narrower filter cuts neighbors and muffles the voice. Adjust it whenever there is adjacent interference.

Etiquette

The receiver belongs to a volunteer. The antenna, electricity bill, and internet bandwidth are theirs.

• Respect the time limit. Many owners set a maximum time per visit or per day. When it ends, switch to another receiver.
• Close the tab when you stop listening. On a four-slot KiwiSDR, a forgotten tab takes up someone else's spot.
• One connection per person. No opening the same receiver in multiple tabs.
• No robots. A script that stays connected, sweeps bands, or collects audio or data continuously only with the owner's authorization.
• Continuous recording, upon request only. Recording an amateur radio or broadcast snippet for study is normal. Aviation, maritime and private services, not even a snippet: listening is allowed, recording and sharing are not (see what you can listen to and publish). Leaving it recording for hours, or retransmitting the audio elsewhere, requires prior agreement. Contact info is usually on the page itself.
• Identify yourself properly. Several receivers ask for a name or callsign. Type yours.
• Give credit. When publishing a screenshot or audio, state which receiver it came from. And check beforehand what can be published.

If a receiver is bad (high noise, deaf antenna), switch receivers instead of complaining. Whoever keeps that thing on the air does it for pleasure.