High Visibility Digital Mode Text
for Hams with Impaired Vision


   This article is for amateur radio operators with impaired vision who are interested in using HF digital text modes such as RTTY and PSK31. To use these modes hams usually send signals over the air using a transceiver that is connected to a personal computer. The operator enters text via the PC keyboard and reads incoming messages on the computer screen.

   This article describes how hams with impaired vision can make the incoming text easier to read using large text, magnification, and a high contrast color scheme. Two different digital mode programs are used in the examples:

TrueTTY has built-in options for customizing text and

                       background colors.

Ham Radio Deluxe Digital Master 780 (DM-780) has

                     only limited format options, but the visibility can be

                     enhanced with magnification software.

   Fldigi, another digital mode program with high visibility text options is described in an article for Windows/Macs and and article for Linux. Fldigi is also pre-installed on the fldigiVI LiveUSB.

   MultiPSK, another digital mode program with text options, is described in a separate article.


TrueTTY is a program for amateur radio digital text communication via a sound card. The program menus are designed for easy use, and the documentation is good (Help Menu → Contents → Program Overview). The WM2U web site also has information about the program, including a page on "Hook-Up," covering various options for homebuilt and commercial PC-to-radio interfaces.

   The TrueTTY program options for customizing text and background colors are in the Setup Menu under the Fonts and Colors Tab. Figure 1 shows the TrueTTY Window with 24 point bold type in both the Received (upper) Text Box and the Transmit (bottom) Text Box. The Figure is shown actual size. On a typical display set for 120 dots per inch the received text height is 0.3 inch. As illustrated in the following section, a third party magnification program such as ZoomText can also be used.

Figure 1. TrueTTY Window (actual size with large, bold text)



   The reduced window width used in Figure 1 hides three control buttons at the top right, including the important Transmit button. You can still operate all three buttons with keyboard shortcuts. For example, Alt-T toggles the Transmit button.

   Many font and background color choices are available in TrueTTY to improve visibility. Figure 2 is an example of a high contrast black and white scheme.

Figure 2. TrueTTY Window (actual size with high contrast text)



   A separate article describes how to configure the TrueTTY vision features.

Ham Radio Deluxe DM-780

   Although the basic Ham Radio Deluxe program has menu options to make the display easier to read (see the rig monitoring article on this web site), the DM-780 program does not include these options. In the DM-780 window shown in Figure 3 the text size is small, and it is not adjustable. On a typical 22" PC screen set at 120 dpi the text is 0.1 inch high. The Text Size Menu is greyed-out.

Figure 3. DM-780 window (red labels added)



Windows Magnification Software

      For small text, even a little magnification results in an image that is difficult to read. The original screen pixels are prominent, making jagged and blurred letters. This effect severely limits the usefulness of the Magnifier accessory included with Windows operating systems. Even with this limitation, however, Magnifier can be used to test whether magnification is helpful. You can also determine whether the necessary magnification makes it difficult to follow the characters as they stream across the screen.

     On Windows Vista and Windows 7 systems the Magnifier is located in the Ease of Access folder:  Start → All Programs → Accessories → Ease of Access → Magnifier. If the controls are hidden, click on the Magnifer name in the Status Bar at the bottom of the screen.

     If magnification seems like a promising approach, you can test one of the third-party programs that use anti-aliasing to produce high quality magnified text. The following section gives an example.

Using ZoomText With DM-780

ZoomText and ZoomText Express are programs that enhance the visibility of PC displays. Both programs offer the same high contrast color conversion, but the magnification is limited to 2x with the Express version.  The ZoomText toolbar shown in Figure 4 has a number of display options.

Figure 4. ZoomText Toolbar



     The toolbar includes other useful visibility-enhancing features, such as high-contrast color conversion and customized mouse pointers. However, the optional Reader software does not recognize incoming DM-780 text in real time.

     The multicolored waterfall in Figure 1 is a useful display of the spectrum of received signals. The horizontal axis represents frequency; signal strength is color-coded; and the display scrolls downward in real time. Signals show up as vertical tracks with shapes that help identify the mode being used (eg, PSK31 and RTTY). You can tune to a signal by clicking on it with the mouse.

     Magnifying a large area of the moving waterfall can cause difficulty for the ZoomText program. The cursor may move randomly at times if the entire waterfall is displayed. (This was observed on a PC running Windows Vista with a 2.6 GHz Intel Dual-Core processor and 3 GB of RAM.) The problem can be avoided by decreasing the height of the waterfall window to that shown in Figure 3.

   Figure 5 shows the Received and Transmitted text boxes compressed to be visible in the same ZoomText window. The text in Figure 3 was first magnified with 6X power to fill the computer screen (which is shown at 40% actual size).

Figure 5. DM-780 text boxes filling the screen at 6X power (shown 40% actual size).



   Too much magnification can make it difficult to follow the characters as they stream across the screen. The goal is to select a power that makes the text readable while at the same time allowing you to view a complete line of text without moving the window. There is a tradeoff between magnification and the number of characters in a line.

   For a typical 22 inch display using 120 dots per inch, DM-780 text at 6X power is 0.6 inch high, and the screen width is approximately 28 characters. The Table shows how the text size and line width on this display vary with the power.

PowerText HeightLine Width

       2X                     0.2 inch                        82 characters

       3X                     0.3                                55

       4X                     0.4                                42

       5X                     0.5                                33

       6X                     0.6                                28

       7X                     0.7                                24

       8X                     0.8                                21

   It helps if your contact sends short lines of text.

   After a magnification program is closed, the text may be lighter and less sharp. This occurs if the program turns off the Windows Clear Type effect. To restore the setting in Windows Vista and Windows 7: Right-click on the Desktop → Personalize → Window Color and Appearance → Appearance Settings dialog → Effects → Use ClearType → OK → Apply → OK.

   Free trial versions of the ZoomText programs can be downloaded from the Ai Squared website.


  TrueTTY has a range of built-in text sizes and high contrast color options for improving visibility. It can also be used with a magnifier program.

   Ham Radio Deluxe DM-780 has limited display options, but magnification and color contrast software such as ZoomText can be used with it.

   Programs like ZoomText and ZoomText Express use anti-aliasing to produce higher quality text images than the Windows Magnifier accessory.


   Thanks to Sergei Podstrigailo, UA9OSV, the author of TrueTTY, for answering questions.

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. 9/6/2014

                 Related Articles: Configuring TrueTTY

MultiPSK Accessibility

Digital Mode Text-to-Speech

Rig Monitoring for Vision Impaired Hams

Magnifying Ham Radio Program Displays

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