170 Hz has been the world wide standard for a long time. But then we got things like AMTOR using a 200 Hz shift, so things like the PK-232 compromise and use the same shift for RTTY. Which is why some sound card RTTY demodulators are able to hunt for the correct shift and adapt to it. I haven't heard of 182 being a standard for anybody, but then there are lots of things I don't hear of anymore.
850 Hz shift is just about never used by amateurs anymore. One use, that may be no longer extant, was for Clatternet which is/was a get-together using military equipment that is capable of only 850 Hz shift, and perhaps 85 Hz shift as well. Another was that I used to promote a Green Key event to celebrate the beginnings of FSK on the HF ham bands, and for that we would try to use 850 Hz shift if possible to re-create the experience of the hams back in 1953 when it first became legal. At that time the 850 Hz shift was mandated by the FCC; permission to use anything less came later. I think it's interesting to have 85 Hz shift, who I have never heard anybody using it, because that is perfectly acceptable with today's equipment and is a standard for carrier telegraph systems operating up to 75 baud. One reason we used such wide shift in the old days was that the transmitters and receivers drifted so much that you needed wide shift to reduce the amount of time you had to spend retuning. Then K6STI was advocating 850 shift because that gives you a substantial frequency diversity of mark and space channels, so that independent detection might better allow you to work through selective fading and QRM. Jim W6JVE jhhaynes at earthlink dot net _______________________________________________ fldigi-alpha mailing list [email protected] https://lists.berlios.de/mailman/listinfo/fldigi-alpha
