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August 13th 03, 12:18 AM
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Subject: NCVEC Position on Code
From: Floyd Davidson Date: 8/11/03 3:22 PM Eastern Daylight Time Message-id: "Dick Carroll;" wrote: Floyd Davidson wrote: The problem is you are comparing two different data rates through the same channel. PSK-31 runs at 31.5 bits per second. If you used CW at that rate, it works out to about 37.8 wpm. Are you telling me *you* can copy 35 wpm using a 200 Hz filter when there is Doppler distortion from auroral activity? Can you, Floyd? No, you idiot- do you come from the same village as Burke?- What I said is that we REAL HAMS have no NEED to invoke laboratory nonsense to interfere with our on the air operation! ANd they are NOT THROUGH THE SAME 31 cycle channel! They both come through the channel tha *I* set, not Shannon, which was a 2.4 kc channel which is modifiable by all those snazzy IF Sounds as if you, like Larry Roll, don't want to have anything to do with any of that "Empirical Theory" stuff of his, eh? Perhaps I remembered the previous discussion incorrectly? Were you using a 2.4 KHz channel, or a 200 Hz channel? In either case the agc, and hence SNR, are affected by the noise in that channel, not the 30Hz filter in DSP software. Only if the AGC was turned on. In many situations, reception can be improved by disabling the AGC. Old CW operator's trick. But once again, Shannon *does* apply to everything you've got there. *If* you want to actually understand it, that is the *only* way to explain it. Shannon's work sets a limit. Real world performance cannot be "better" than Shannon predicts. But it can be worse. Or you can continue to be a glorified CB operator. Have you ever actually used PSK-31, Floyd? In fact, what you've done is demonstrate that Shannon's work *does* apply to ham radio! PSK-31 is an m-ary channel using QPSK (where m = 4), which trades signal to noise ratio for bandwidth to obtain the same data rate as it would using straight phase modulation. Which is good in some situations and not so good in others. What *you* should be saying is that your experience demonstrates that Shannon's theories prove true in the practical application of ham radio. When the SNR is low, CW can be useful, albeit at very low data rates, if restricted bandwidth is a requirement. Of course, if the bandwidth wasn't restricted to 200 Hz, almost any variation on PSK modulation would out run CW for efficiency, as can easily be demonstrated using Shannon's formula. That depends on how "efficiency" is defined, doesn't it? If we count the power required to operate the radio and the power required to operate the laptop, PSK-31 isn't that "efficient".... Yeah, Frosty, most of us know all that, it's been well published, and quoted here for some time. But it still has no applicability to ham radio outside the theoretical. Apparently your Empirical Theory is a little sparse there DICK. Why and how do you think PSK-31 was invented to begin with? I happen to know the answer to that question. The inventor and his helpers were interested in a very narrow bandwidth "keyboard to keyboard" mode to replace Baudot RTTY. It clearly does have practical benefits, and when you attempted to use PSK-31 you *were* making use of those benefits. Of course. OOK CW has benefits, too. Yet it seems to bother some people to admit that. It is interesting to note that Larry Roll and Dick Carroll have actual experience with PSK-31, while Brian Burke, Floyd Davidson and Len Anderson have none. Yet the latter insist upon denying the experience of the former. And vice versa. Why not just use the mode you like best and have fun? If PSK-31 is so wonderful, why is it that only two of the five named have actually used it? |
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