Hell text is "painted" to the screen as the Hell tone is being received through the sound card. To receive a Feld Hell signal, the computer program sets up the sound card to use DSP techniques for detecting the signal and places the output on a short vertically scanning line that is moving horizontally across the screen. This action produces a single line of text in a marque fashion that gets wrapped around to eventually create a full screen of text. Really simple! The computer never has to decide (decode) the characters and so no missed characters or wrong characters will ever be sent to the screen! To send Hell characters, the computer program uses the sound card to produce the audio signal to modulate the transmitter in the same way that other sound card modes are transmitted. For Feld Hell, it is an on/off single tone the same as used for MCW. Each tone burst is conditioned by the DSP to have the correct shape that will not cause harmonics and "clicks" to be produced by the radio's modulator. A properly adjusted Feld Hell input level will produce a bandwidth of no more than 75 Hz. Over driven levels will appear as wider signals on the waterfall display.
With Hell modes, the only time that a received character appears wrong on the screen is when it is typed wrong at the other end. The only time when a character or word is not readable on the screen is when radio propagation is so bad that not even DSP techniques can pull it out of the mud! This occurs at signal levels considerably lower than those tolerated by all other modes. The weakest link in decoding Hell characters will be the operators ability distinguish letters under noisy conditions. Another advantage of Feld Hell mode over most others is the ability to print readable text under conditions of polar phase shift. A severely phase shifted signal will print a shifted character, but it can still be read on the screen. Each Hell character is sent on a double line, so that if one character is shifted off the marque, the other will still be visible. Another nice feature of Feld Hell is that the RF power output cycle is less than 50% during TX, saving energy. One nice feature that feld hell has in common with PSK31 is a very narrow bandwidth used by the signal (about the same as for CW). The end result is the most reliable keyboard communications achievable on HF ham radio. So why isn't everyone using Hellschreiber mode?
How does Feld Hell compare with PSK31?
PSK31 is a true digital mode and for some people that makes it a "sexier" mode than Hellschreiber. Hell modes are more closely related to CW than to other digital mode. With CW you use your ears and for Hell modes your eyes. Having both fuzzy and digital modes available on the computer desk top has been a good strategy for me. The Hellschreiber frequencies are next to the PSK31 frequencies on most ham bands, so they are easy to mix. As more PSK31 ops discover how nicely the two operating modes compliment each other, we will see more Hellschreiber activity.
What about the other Hellschreiber modes?
The very popular Hellschreiber freeware program from IZ8BLY and the Shareware program from UT2UZ have other experimental Hell modes included. Of these, there are two modes besides the traditional Feld Hell mode that hams have found to be useful and are currently using. PSK HELL and FM HELL modes both come in a 105 baud and 245 baud rate. With these modes, the ON/OFF keying needed to paint the Hell characters across the marque are sent by shifting the phase of two tones (PSK Hell) or by shifting the frequency of one tone (FM Hell). The faster baud rate for both modes does not increase text speed, but it does increase resolution, producing a sharper font. Both modes have a 100% duty cycle during transmit, but the additional power will produce a less noisy background, making the text easier to read. With either of these modes, it is fun to see the font flow across the screen like a video, as apposed to computer type set. When your eyes get tired of reading computer text, try Hell modes!
What does NB6Z recommend?
Go to HELL modes if you are serious about sound card DSP keyboard operation! Download Nino's or Nick's program now and see for yourself! These are well tested programs that will NOT mess up your PC or other applications. You will find several useful features like macros, type ahead and canned message buffers. You can bring up your own logging program and other sound card programs from a menu. The screen text size can be enlarged if needed. Sound card adjustments can be made from within the program.
Read more about Feld Hell at www.qsl.net/zl1bpu/fuzzy/feld.html .
