WebSDR Accessibility
for Blind & Vision-Impaired Hams


   A webSDR is a software-defined amateur radio receiver that can be operated remotely over the Internet. Multiple hams can use a single webSDR receiver independently. For example, 20 operators around the world might use a webSDR receiver at the same time, each tuning and listening to a different station.

   They are open for free use by anyone with a broadband Internet connection. A ham license is not required.

   This article is about the accessibility of webSDR receivers for blind and vision-impaired operators.

webSDR Receiver Locations

   The server software that makes webSDR receivers available over the Internet was developed by Pieter-Tjerk de Boer, PA3FWM. His Web site includes a directory of the locations and URLs of active webSDR servers as well as a real-time count of the current users of each one.

   A world map at the bottom of his Web page shows the station locations. Typically, there are 80 or more active servers with the majority in Europe and eight or more in the U.S.

Frequency Coverage

   The webSDR.org directory is annotated with the frequency ranges of the receivers at each location. Each station has from one to six software-defined radios (SDR), mostly SoftRock models.

   Each SDR is tuned to cover a fixed frequency range, usually 192 kHz wide, within the amateur radio allocation for the locale. When you change bands via the Web interface, you are switched to a different receiver in the station.

webSDR User Interface

   Figure 1 shows the Web interface of the Maxwell Foundation station at the University of Eindhoven, Netherlands. There are four ways to tune the receiver: (1) Select a signal by clicking on the frequency bar below the waterfall display. (2) Drag the filter pass-band diagram (Figure 2) located below the frequency scale. (3) Type a selection directly in the frequency box. (4) Click on a stepwise-tuning button below the frequency box. On some other webSDR station Web sites you can also tune by scrolling the mouse wheel when the pointer is on the waterfall frequency scale.

   The filter bandwidth is adjustable by dragging one side of the filter passband diagram or via buttons in the Bandwidth box.

Figure 1. WebSDR User Interface.

 Figure 2. Filter Passband Diagram.


   On a standard 22" LCD display at 120 dpi, the width of the waterfall is 11.3", and the default height shown in Figure 1 is 1.1". The large option display is 2.2" high. Most text is 0.1" high, and the filter passband diagram is 0.2" high.

  The user interface works well with magnification software, including the Windows Magnifier Utility. (Depending on your computer, magnifying a large waterfall area may cause the cursor to move erratically. In that case, select the smallest waterfall size option in webSDR, and use the default "slow" speed for scrolling.)

Screen Reader Access—Windows

   JAWS screen reader users can operate the webSDR user interface. You can use the Tab key to reach the tuning controls, which include a frequency entry box and stepwise-tuning buttons.

   The band selection buttons are not accessible, but band switching is automatic when you enter a frequency in a range covered by one of the receivers in the station.

   To use the Tuning controls, first link the JAWS cursor to the PC cursor [Insert-NumPad-Minus]. Tab down until JAWS says "frequency" followed by the default setting. Enter a frequency in kHz, eg, 14150 (no Enter key), and the audio begins.

   Tab once to move down to the row of six stepwise tuning buttons. From left to right:  The "---" button moves down 2.5 kHz. The second button "--" moves down 500 Hz. The "-" button moves down 50 Hz. The "+" button moves up 50 Hz. The "++" button moves up 500 Hz. The "+++" button moves jup 2.5 kHz.

   Before tuning, press NumPad Minus once to select the JAWS cursor. Now you can select a button by pressing Tab to move to the right and Shift-Tab to the left. Use Enter to press a button. JAWS does not tell you which button the cursor is on. (You can hear button names after each Tab by pressing NumPad Plus, but must then press NumPad Minus before the Enter key will press a button.)

   To enter a new frequency, Shift-Tab back to the first button, "---". (If you go past it to the frequency box and the frequency is spoken, Tab forward to the first button.) Select the PC cursor [NumPad Plus], Shift-Tab to the frequency box, and enter your frequency.

   The View menu box above the waterfall includes an option to reduce the Internet bandwidth required for webSDR by hiding the waterfall. As you Tab down from the top of the page and reach the View menu, JAWS voices the current setting, usually "one band." Press the Down Arrow to select "Blind."

Screen Reader Access—Mac

   If you use the Safari browser, the VoiceOver screen reader works well with webSDRs. It is easier to use than JAWS with Windows as described above. No switching between types of cursors is required.

   Tab down to the frequency box, where VoiceOver speaks the current setting. Type the frequency in kiloHertz (no Enter key), and the radio is tuned. Tab to any of the incremental tuning buttons (or Shift-Tab back), and press Enter to click on the button. VoiceOver speaks the frequency-step to identify each button.

Receiving Digital Modes with webSDR

   A separate article describes how to use a digital modem program to decode the audio from a webSDR.

   Figure 3 shows a PSK31 signal received from Ukraine by a webSDR in the Netherlands and decoded using fldigi on a Windows computer in the U.S.

Figure 3. fldigi decoding a PSK31 signal from a webSDR receiver.



WebSDR and Java

 On the WebSDR site, PA3FWM, explains that until July, 2014, the software required a Java-enabled browser on your computer. In January, 2014, a Java security update from Oracle made the WebSDR program more difficult to use. To access a WebSDR radio, it became necessary to enter the URL in a list of acceptable Java sites.

   In July, 2014, PA3FWM updated the WebSDR software so that Java
is no longer required. The software uses HTML5 WebAudio instead. He points out that the updated software does not work with Internet Explorer and older versions of other browsers.

For More Information


   Digital mode reception using a webSDR.


   A webSDR receiver can be operated remotely over the Internet. Using only a Web browser, blind and vision-impaired operators can tune and listen on the ham bands using software-defined radios located around the world. 

Author Information

   Peter DeNeef, AE7PD, is an Extra Class amateur radio operator in the U.S. This Web site has no ads or conflicts of interest.
Email:  HamRadioAndVision "at" gmail "dot" com.

rev. 11/23/2015

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