HDSDR Accessibility
Operating a Software-Defined Radio


   HDSDR is an application program for operating software-defined radios, such as the popular SoftRock models. The program defines both the user interface and the radio functions. This article describes the accessibility of HDSDR for vision-impaired amateur radio operators.

   Features of special interest include a high-visibility RF spectrum & waterfall display, a separate AF spectrum, and keyboard shortcuts for operating without a mouse.

HDSDR Software

HDSDR is freeware for Windows computers, written and distributed by Mario Taeubel, DG0JBJ. It is an SDR application program that is often used to operate soundcard-based software-defined radios.

   For example, HDSDR is recommended in the software installation instructions for SoftRock radios and in the Elecraft KX3 Owner's Manual section on SDR applications.

   General information about HDSDR is on the Frequently Asked Questions page by the author.

Radios That Work With HDSDR

   DG0JBJ maintains a list of hardware SDRs that work with HDSDR. A link for each radio gives information about how to connect the application to the radio.

   For most of the radios in the list, HDSDR controls the local oscillator frequency over a USB connection via an ExtIO DLL file written for the particular radio. Some DLL files are available on DG0JBJ's site, and some are linked on radio manufacturer Web sites. The DLLs used by HDSDR are often called "Winrad ExtIO files," named for the open source Winrad SDR application code that HDSDR is based on.

   After unpacking the zip archive of the ExtIO DLL file for the radio, you copy the contents into the Windows Program directory for HDSDR (typically C:/Program Files (x86)/HDSDR/).

   The Elecraft KX3 is one of the exceptions. Instead of using an ExtIO DLL, HDSDR can control the KX3 VFO with OmniRig, a free CAT control program by Alex Shovkoplyas, VE3NEA. In that case you can tune the KX3 with either the hardware VFO knob or HDSDR. The KX3 radio, including its SDR firmware, functions as usual. HDSDR running on your computer uses the I/Q output from the RF front end of the KX3 and serves as a panadapter.

   Details about using HDSDR with a KX3 are in the link in DG0JBJ's hardware list. The "SDR Applications" section of the KX3 Owner's Manual has additional tips.

User Interface

   The user interface (Figure 1) is designed for operation with a mouse or keyboard shortcuts. For a list of the shortcuts, click on the Help/Update button or press the [F1] key and select Keyboard Shortcuts.

   HDSDR is not accessible to screen readers.

Figure 1. HDSDR user interface.


   The menus open via four buttons in the lower left corner of the control panel (Figure 2):  Soundcard [F5], Bandwidth [F6], Options [F7], and Frequency Manager [Control+B].

Figure 2.  HDSDR console detail.


   The upper (RF) spectrum and waterfall are centered on the local oscillator frequency (LO). The displayed bandwidth is determined by the sound card bandwidth and the input sample rate selected in the Soundcard menu [F5]. For example, if your sound device provides 96 kHz bandwidth and the local oscillator setting is 14.2 MHz, the RF spectrum will be nearly 96 kHz wide, centered on 14.2 MHz.

   The lower (AF) spectrum and waterfall show the tuned signal in more detail. In the AF spectrum window you can change the audio filter width by dragging the upper and lower bandpass indicators (red lines).

User Interface—Tuning

Some ways to tune within the RF spectrum display:

1. Click on a frequency.

2. Click and drag the shaded vertical area in the spectrum, which represents the bandwidth of the audio filter.

3. Scroll up or down in frequency with the mouse wheel in Tunemode (Options > Mouse wheel > Mode: Tune).

4. Type a frequency, and the Fast Frequency Input featureautomatically opens the Enter New Frequency dialog.

5. Click on the "Tune" label (to the left of the frequency readout)to open the Enter New Frequency dialog.

6. Left-click on a digit in the frequency readout to increase andright-click to decrease the digit.

Some ways to change the local oscillator frequency

    To display a different segment in the same band or to change bands:

1. Left-click and drag the frequency scale that separates the spectrum from the waterfall.

2. Scroll the local oscillator frequency with the mouse wheel in "L.O. mode" (Options > Mouse wheel > Mode: L.O.).

3. Type a frequency, and select the LO button in the Enter New Frequency dialog.

4. Right-click on a new tune frequency in the RF display (new in HDSDR v2.60). The LO resets to 10 kHz below the desired signal frequency. For example, a right-click on 7.20 MHz centers the display at 7.19 MHz and tunes the receiver to 7.20 MHz. You can change the 10 kHz offset (Options > Misc Options > Set LO/Tune Offset).

5. Click on the "LO" label to the left of the digital readout to open the Enter New Frequency dialog. Enter a local oscillator frequency.

6. Select the Quick Tune option in the Enter New Frequency dialog. Entering a new frequency automatically tunes to the chosen frequency with a preselected LO offset

          (Options > Misc Options > Set LO—Tune Offset).

7. Left-click on a digit in the LO readout to increase, and right-click to decrease the digit.

8. Use the keyboard shortcuts [Control+PageUp] or [Control+PageDown] to move the LO up or down in steps.

9. Click on one of the small red arrowheads at the ends of the frequency scale separating the spectrum from the waterfall.

10. The HDSDR Frequency Manager makes it easy to change bands by clicking on the FreqMgr Button. The Ham Bands Tab in the Frequency Manager Window displays preset local oscillator and tuned frequencies. The User Tab lets you create your own list.

   The Frequency Manager lists are stored as files in the Documents folder [Documents > HDSDR > CSV is typically C:\Users\{Username}\Documents\HDSDR\CSV.] There are several ways to edit the presets: (1) You can enter the current HDSDR settings with  the "Get Current" and "Add" buttons in the Frequency Manager Window. (2) Edit usr.csv directly with a spreadsheet program. Or, (3) Right-Click on usr.csv and select "Open with NotePad."


   The main window is adjustable up to full-screen size. By right-clicking on the frequency scale between the RF spectrum and waterfall you can change the relative sizes.

   The default "Filled [with color] Spectrum" option for better visibility is shown in Figure 1. There are six options for the color scheme of the spectra and waterfalls (options > Color Palatte).

   Text size is not adjustable, and it does not change with the window size. On a standard 22" display at 120 dpi much of the text is 0.1" high and some is smaller, so a large screen and magnification might be helpful. The digital readouts of frequency and local oscillator frequency are 0.25" high.

   The display is customizable:  The RF and AF bandscopes can be swapped, removed, or displayed as a panadapter without any HDSDR controls.


   The high visibility RF spectrum and waterfall display in HDSDR have adjustable size and a choice of color schemes. The separate AF spectrum and waterfall show the tuned signal in greater detail. Keyboard shortcuts can be used instead of a mouse for many of the program controls. 

   The text size is small, so a large screen and magnification might be helpful.

Author Information

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

rev. 7/1/2013

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