The M100 is just the thing for 5 working HF DX, but it is necessary to change the speed for reception of different HF signals.
Like many other amateurs, I had my introduction to the world of RTTY on the two metre band using a computer or "glass" system. This gave much pleasure, both in its' design and construction, also its operation. It speed opened up a whole new world of repeaters, mailboxes and many new friends. After a time, I began to wonder if similar Pleasure could be achieved from HF operating with this exciting new mode and, in due course, an interface with the HF rig was arranged.
At first the bands seemed alive with signals but it was not long before it was realised that these signals were, in fact, emanating from the computer - a potent source of interference with its master oscillator right in the middle of the 20-metre band and all those digital ICs merrily switching and generating "birdies" witt up into the VHF spectrum. Initially, conventional means were tried to alleviate the problem - screening, optocoupling, etc - but, eventually I had to admit defeat. This was when I met my Marvellous Mechanical Mistress - the Siemens Model 100 teleprinter.
The M100 was just the thing for HF DX operation but it soon became apparent that there were different speeds being used on HF. Whilst it may be easy to change the speed of a computer RTTY program by merely pushing a button, it is quite another matter with the electro-mechanical governor in the M100.
Figure 1: M100 Speed Controller. (Note: Operational Amplifiers are LM3900.).
VK3DOC, Morris Odell.