Projects

PICAXE-08M2 Sequential Multi-Tone(SMT) QRS Hellschreiber and Morse Code ID Generator

PICAXE-08M2 Sequential Multi-Tone(SMT) QRS Hellschreiber and Morse Code ID Generator

*******************[ Experimental ]*******************
*                          V.2                       *
*                      PICAXE-08M2                   *
*               Sequential Multi-Tone(SMT)           *
*          Slow-Hellschreiber and Morse Code ID      *
*   Can be used as a QRSS, FSCW or DFCW Generator    *
*                                                    *
* Using calibfreq tweaks to narrow freqency shift   *
* Decode with Spectran V2 horizontal waterfall      *
* https://digilander.libero.it/i2phd/spectran.html *
*                                                    *
*      Easy MULTI-MESSAGE MODIFIED by rhb.20230811   *
*                                                    *
*      radioSPARKS VE3XRM rhb.20230908 last edited   *
*            Feld Hell Club Member - FH7439          *
*                                                    *
******************************************************

Hellschreiber (Also known as Feld Hell or just Hell) is a teleprinter system developed in the late 1920's by Rudolf Hell, a German inventor.

Slow-Hellshreiber is a frequency shift keying (FSK) slow-speed variant of Hellschreiber, that is compatible with slow-speed narrow bandwidth weak signal modes such as QRSS, FSK/CW etc.

The figure shows the principle behind displaying the matrix of dots making up the characters.

The sequence of rising tones make up a staircase waverform, which, repeated at definite intervals, form a sawtooth across the band of frequencies forming the character.

S/MT HELL
Sequential tone Multi-Tone Hellschreiber is a frequency domain technique, and as such requires FFT demodulation. It represents something of a half-way house between Feld-Hell and C/MT-Hell. On the one hand, like Feld-Hell, it is a sequential transmission technique, yet like C/MT-Hell, it is a frequency domain technique. Unlike Feld-Hell and C/MT-Hell, S/MT-Hell is believed to be a modern (1998) invention.

S/MT-Hell characters are sent using a modified raster scan method, where the timing of the pixels is unimportant, so long as the sequence is maintained and the speed kept relatively constant, both to preserve character shape. There is no synchronism, and no accurate timing of the scanning process is necessary. In addition, within limits, the non-printing pixels can be omitted, ie. not sent at all! The advantages of S/MT-Hell are speed, immunity to timing and time domain interference, simplicity of signal generation and ease of transmission. In addition the transmitted power is concentrated in a single dot, like Feld-Hell, so performs well with low power.

Are we having fun yet, You betcha! I love this little chip (MCU).

Working with OLED displays and getting more ideas. The fun never stops. I made an epiphany discovery about the Hellschreiber font.

The OLED character font bit format is exactly the same as the Hellschreiber 5X7 character font bit format!
Hellschreiber was invented first, though, about a hundred years ago.

I modified my version of a Morse code ID generator to scan the OLED font. That worked. Both MORSE and HELL subroutines are separated to see how they work. Can be opimized by combining.

The bandwidth use was way too wide. Then I found the only bit of code on the PICAXE forum and it used a trick to shift the internal clock of the PICAXE using the command CALIBFREQ

Hellschreiber Forum Disscusion #13304

This is not a true HELL mode but a way to paint to a spectrum display to be human readable.
Used a microphone input to the Spectran software for a curtain display with good results. (see image for settings I used)
The piezo can reproduce the harmonics and Spectran can decode these. I would not use this square wave output on a transmitter.
Better to use the DAC output (with FET OPAMP Buffer) to directly modulate the VFO Varactor tuning.

To learn more about Hellschreiber follow the links:
NOTE: Due to the longevity of the forum, links in the future might fail.
Hopefully ARCHIVE.org would have captured the pages.

Core Code samples and KB reference material from:

Hellschreiber Forum Disscusion
About everything that is related to "Hellschreiber"
Introduction to Hellschreiber Modes
Hellschreiber Modes - Technical Specification

Signal Identification:

Hellschreiber Signal Identification Guide