Retro design: the DJ6HP RTTY convertor


This ancient paper document of the DJ6HP convertor already is in state of pulverizing…
Before it is unreadable and vanished for descendants: this appendix contains almost everything that is needed for building of the DJ6HP convertor (in German).

Thousands of times the DJ6HP convertor has been used for RTTY QSO’s. It proved to be a fine mode for usage at HF, especially for DX on the 40 meters band that daily was plagued by manmade interferences like broadband cracklings signals from long distance radar and illegal, high powered AM broadcast stations.

The RTTY convertor shortly: RTTY signals sounds with two alternating standard tones.
After a right receiver tuning the audio passes through the filter system of the convertor activating by those tones an electronic switch. The alternating level on/off for electromechanical systems or for computers 1/0 can be read at the input point of RTTY suited equipment that transforms those codes immediately into readable text.
On the contrary for sending of information RTTY equipment is switching a tone device generating the alternating standard tones as input of the transmitter.

The DJ6HP convertor has been used in combination with various input/output equipment: uart–intelligent terminal, T37- mechanical type writer from Siemens, CBM64- Commodore home computer with the program COM-in64, IBM home computer using DOS or previous versions of Windows.

Computer techniques improved and since 1980 the number of computerized communication modes was growing fast: Packet Radio – also for HF, even CW, Facsimile, SSTV. It was reducing the number of spotted RTTY stations.

The last decennium there are much efforts for modes that try to tackle noise. BPSK is very popular since 10 years and is very robust in an environment of many active stations.

Nevertheless at talks with radio amateurs and listening on the HF bands it is concluded that RTTY mode is still alive and its activity seem to be rising again. Reasons to restore documents of the technique.

Note PA2ION: originally this RTTY convertor was developed for mechanical telex machines with larger mass inertia. Computers and similar equipment react much faster and have by that much better results when applying filtering of incidental, fast spikes accompanying data pulses coming from the convertor. Application of a trimmed RC network and optical isolation of the signals improved text conversions significantly and is combined with use of opto-couplers also much safer for computer port electronics.

Ron, PA2ION (Augustus 2015)