Helmuth "Jimboy" Meyer DJ2EI, provides this basic explanation for the RT-3.

"The RT3 Rapid Transmitter for Morse Code is used with the SP 15 as well as with the transistorized transmitter SP 20, where it is named "Kurz-Signal-Geber KUG". The transmission speed is approximately 250 words/minute.

It is a small, heavy and robust mechanical device which can store 25 selected characters for each message burst. Only ten different characters are available for selection, ten discs on a shaft have been  fixed coded at the factory.

These ten discs are e.g. coded as follows:

1= W   2= F   3= V   4= R   5= 5   6= K   7= B   8= L   9= G   0= M
.--    ..-.   ...-   .-.    .....  -.-    -...   .-..   --.    --

This was the coding for the German Bundeswehr versions.

It is easy to see that each character has a "mirror" in Morse code except  the figure 5 and the letter M. This is improving the intelligibility at the receiving side and in addition to this every character is sent twice, thus some kind of "forward error correction" is available. A small crank with gears is used to turn the shaft with the ten coded discs".

Selection of the character for each storage place is made by a small tab which can be moved on a rail between positions 1 and 10. The tab closes a contact when the crank is turned so the respective code of this disc is sent out. The RED tab indicates the "start position". On the 6 pin connector pin F is ground and pin B is the "hot" contact.

The speed of the burst transmission is normally approx. 250 wpm. There is also another gearshift built-in for approx. 750 wpm. This is accessible after removing the round black cover.

Because of the limitation to only ten characters instead of the complete alphabet it is necessary to use a 10 by 10 matrix table for ciphering which will give 100 squares for the alphabet, words, figures, or even complete sentences. Thus the ciphered message is twice as long as the plain text. If the ciphered message is longer than 24 characters (which is only 12 characters of plain text !) you have to set and send the first 24 characters (the message burst) and than set and send the next message burst and so on".

RT-63 S/N 1000

All photos in this table via E-bay

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Credits and Contributors:

1)  Helmuth "Jimboy" Meyer, DJ2EI      http://www.spyradio.cabanova.de/

Oct 6/08