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?