PSK31 Operating Notes
from a Blind Ham
by W1BLS and AE7PD
W1BLS is a blind amateur radio operator who has worked more than 100 countries using the PSK31 and RTTY digital modes. In 2008, he posted a blog reporting that blind hams can use the TrueTTY program for Windows. Recently, he switched to cocoaModem because it has additional features and is easier to operate.
This article describes how blind and vision-impaired hams can use these programs.
TrueTTY digital modem software for Windows, developed by Sergei Podstrigailo, UA9OSV, has a number of features that blind and vision-impaired hams can use, including:
• text accessible with a screen reader.
• keyboard shortcuts to operate the program.
• menus accessible with standard Windows commands.
Screen readers are not designed to work in a text window with streaming characters and scrolling lines. TrueTTY can export decoded text to a static file for conversion to speech by a screen reader program. An example of a QSO demonstrates how to use this feature.
TrueTTY Keyboard Shortcuts
TrueTTY has built-in shortcuts that enable you to operate the program without using a mouse.
W1BLS often uses Dragon Naturally Speaking speech recognition software instead of typing shortcuts. For example, saying "Press Alt Letter C" sends the cursor to the TrueTTY QSO Call Sign data field. At that point, his JAWS screen reader speaks the call sign in the box, and the cursor is in position to enter a new call sign.
Tuning and Filter Settings with TrueTTY
W1BLS uses a narrow receiver filter setting, and he tunes with the VFO knob on the radio to find a quiet spot to call CQ. He prefers a 100 Hz wide filter setting on the Icom 7000 for PSK31 and 250 Hz for RTTY. He has also successfully used a Yaesu 857D radio, which has only wider filters.
The center of the radio receiver pass band (displayed on the waterfall) is at the offset frequency 1500 Hz. To set the TrueTTY default receive and transmit frequencies in the center of the passband, edit the TRUETTY.ini file (in the TrueTTY folder in ProgramData) to the values RxFrequency=1500 and TxFrequency=1500.
Configuring the vision-related features in TrueTTY is discussed in a separate article.
CocoaModem is Mac OS X digital modem freeware developed by Kok Chen, W7AY. The cocoaModem PSK modem has accessibility options specifically for blind and vision-impaired hams, including:
• automatic text-to-speech with a customized ham vocabulary.
• special keyboard shortcuts, including access to the waterfall.
• scanning for PSK signals.
These features augment the VoiceOver screen reader built into Mac OS X.
CocoaModem has an incremental (word-by-word) text-to-speech option that automatically speaks or spells a new word when it is received or transmitted. The VoiceOver screen reader is also available to read text, but Incremental Speech works automatically—much easier than typing VoiceOver commands to select and read each block of received text.
An automatic spelling option (one letter at a time) is useful for copying weak signals that result in "noise characters" in the text.
The quality of Mac OS X text-to-speech is excellent, and W7AY has added an extensive list of vocabulary substitutions that make spoken ham messages easier to understand.
Tuning and Filters with cocoaModem
The tuning method described above for calling CQ can also be used with cocoaModem. Direct Frequency Access enables you to select the offset frequency using the keyboard and then tune using the radio VFO knob.
The PSK Scanner in cocoaModem makes it possible to answer a CQ call. In that case, the radio receiver filter should be wider, so the PSK Table View can monitor a range of frequencies. Voice Assist speaks the offset frequency of your signal.
QSO examples with more details are on a separate page.
Setting Received Audio Level
When using the sound card in a PC for text-to-speech, it is advisable to use a second sound card for the modem program. A number of commercial interfaces have a built in sound card for that purpose.
Most modern transceivers output audio in two forms: (1) The audio level from headphone and speaker jacks is controlled by the AF volume control. (2) For many radios, including his Icom 7000, the level of the audio from the accessory jack is not affect by this control. W1BLS uses the audio from a headphone/speaker jack so he can monitor it and adjust the level to avoid over-driving the sound card.
Listening to the received audio also lets him (1) verify that the text-to-speech software is working and (2) monitor the signal-to-noise level.
To isolate the audio of a single station, W1BLS uses a narrow receiver bandwidth (eg, 100 - 250 Hz). The narrow filter can also prevent a nearby strong station from overloading the receiver.
Setting Transmitted Audio Level
If the level of the audio from the sound card to the transmitter is too high, it can trigger ALC activity, distorting the signal and causing RF interference. W1BLS connects the audio from the sound card to the Mic-In jack on the radio so he can use the Mic Gain as a convenient audio level controller. He uses the radio Monitor function to make sure the level is not too high and verify that the modem is transmitting.
The cocaoModem User Manual has an excellent explanation of how to set the audio level (1) below the threshold of ALC activity, (2) above hum and other audio frequency interference levels, and (3) so digital-to-analog conversion by the sound card is accurate (has adequate resolution).
Advanced Operating Techniques
W1BLS often uses a second transceiver with a second modem program running on another computer. He listens to the tones from both receivers simultaneously via Y-connectors at the audio outputs. By choosing narrow receive filter bandwidths (eg, 250 Hz) and by tuning the second receiver, he can monitor the spectra of signals on and around a QSO frequency. The second modem program is configured with a different voice to make it easier to decode the text of nearby stations.
A homebrew RF sensor circuit switches the second receiver off during transmissions. Using a separate antenna with the second radio adds diversity reception, which can be a very useful feature for improving digital mode reception.
More than one copy of TrueTTY can run on one computer, so you can configure one window for PSK and another for RTTY to provide convenient switching between modes.
To monitor the strength and spectrum of his own signal, W1BLS can remotely operate a third receiver at a nearby station.
For More Information
On Windows systems, TrueTTY with a third-party screen reader makes HF digital text modes accessible to blind and vision-impaired hams.
W1BLS gives cocoaModem his highest recommendation. For blind and vision-impaired hams, it is the HF digital modem with the most features and the greatest ease of operation.
Thanks to Chen, W7AY, for his generous help and for making cocoaModem accessible.
W1BlS and AE7PD are amateur radio operators in the U.S. This Web site has no ads or conflicts of interest.
Email: HamRadioAndVision "at" gmail "dot" com.