Back around the early 1980's, QST published a TU (Terminal Unit, what we used to use to interface hardware such as a Model 15 teleprinter to a rig) and it used the then recently developed XR chips. One to produce the AFSK tones and one to decode the tones as a PLL.
This design was actually called a "State of the Art" device in the title of the construction article. This was one of the first PC boards that I ever made and built it from scratch. I sort of worked, but the problem was that the tone decoder could only decode one tone and if you had the slightest QSB across the tones, the minute you lost it, you lost the print until it came back again. It was very hard for me to accept that the ARRL would make such a major misrepresentation of this device. After getting help from long time RTTY operators, they explained that this was not only not state of the art, but was actually a really bad design for HF and could not possibly compete with much older TU's. And they were right. I borrowed an old tube TU and found it so much better performing since it used both tones with a comparator, etc. 73, Rick, KV9U Ralph Mowery wrote: > ...from watching many hours of RTTY with only 170 hz between > >the tones, I have seen one tone fade and come back in >several seconds, then the other tone will do the same >thing. This was observed watching an oscilliscope >hooked to the mark and space filters of an ST-6 >demodulator. > >__________________________________________________ >Do You Yahoo!? >Tired of spam? Yahoo! Mail has the best spam protection around >http://mail.yahoo.com > > > >A >
