Hi Rick, I built one, was horrid! Worked fine on the bench but not so good on the air...went back to the KSR-33 with a TU using passive torroid filters...back when you could get a jolt from an open TTY loop...had a Nuvistor preamp too... state of the art (then)...fun times.
And yes, the selective fading was an issue....still is; one of the reasons 300 baud packet away from the MUF suffers so... Be well, 73 Bill N9DSJ --- In digitalradio@yahoogroups.com, KV9U <[EMAIL PROTECTED]> wrote: > > 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 > > >
