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PA2AGA > HDDIG 03.07.00 23:59l 174 Lines 6855 Bytes #-9412 (0) @ EU
BID : HD_2000_178D
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Subj: HamDigitalDigest 2000/178D
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From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Mon, 03 Jul 00 19:07:54 MET
Message-Id: <hd_2000_178D>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
strength
> >digital transmisson technology can match CW in its' price/performance
> >characteristics, and its' pioneering use of most of today's so-called
modern
> >communications technologies?
> >
> > Peter K1PO
> >
> >"Graham Ranft" <ranftg@interact.net.au> wrote in message
> >news:1uV65.169$JQ6.16999484@news.interact.net.au...
> >> G'day & Greetings!
> >>
> >> I've used both CW and digital. [1200 and 9600 bd. sats packet and
pactor
> >I]
> >>
> >> There is still, I think nothing, quite like the skill and pleasure of a
> >good CW
> >> qso-mine was a cw qso via oscar 13 sending a message from a daughter to
> >> her father on the otherside of the world in hospital.
> >>
> >> Im am now not active, but if I were to go on air again it would be
using
> >CW.
> >>
> >> Let us not flame each other but respect our differing interests.
> >>
> >> Graham formerly VK7ZO and VK1ZO
> >>
> >> Graham in Canberra Australia
> >>
> >>
> >>
> >> .
> >>
> >>
> >>
> >>
> >
>
> Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
> 534 Shannon Way | We break it |
> Lawrenceville, GA | Guaranteed |
------------------------------
Date: Sun, 02 Jul 2000 19:05:21 -0400
From: Gary Coffman <ke4zv@bellsouth.net>
Subject: CW versus hi speed digital etc.
On Fri, 30 Jun 2000 11:26:11 -0500, "Peter O. Brackett" <ab4bc@ix.netcom.com>
wrote:
>CW is a digital mode, it can be high speed, it was the "first" mode as well,
>and it is both machine and human decodable.
While the OOK modulation typically used is in a sense digital, ie an AM
modulation
of on and off states of the baseband signal, Morse Code is not digital. It is
a timing
code. All the coding information is in the timing edges, not in distinct
levels. While
ideally that timing is derived from a fixed clock, in practice it generally is
not and
must be considered more of an analog process.
>Remarkable!
>
>Think about it, it is in fact the only digital mode that is decodable both
>by human operators and machines!
>
>Think about that! Try decoding Baudot RTTY by ear, or PacTor, or Clover...
Actually, some people can decode Baudot RTTY by ear (I can pick out
my own call sign and the RYRYRY signal for example). Each character
does have a distinctive sound if you train your ear to recognize it. Of
course the fact that it is normally sent at 60 WPM or faster makes that
a bit difficult, but slow it down to normal CW operating speeds and it is
not difficult to decode by ear.
In fact FSK is somewhat better (6 dB) than OOK because the ear is
deciding between two distinct signal states and not between the presence
and absence of a single signal against noise, which is a harder detection
problem. In the old days, when using arc and alternator transmitters, where
it was technically difficult to generate OOK, operators used FSK to send
Morse. It worked better than OOK then, and still does. Too bad most Morse
operators got away from that type of moduation. Both machines and men
could take better advantage of it than OOK.
>Try high speed CW on HF with a keyboard program and high speed CW reader
>program, it often works as well as, or better than, at the same speeds, more
>modern digital modes on the HF channel.
But it almost always occupies a larger bandwidth. The sharp timing edges
essential to Morse coding cause the occupied bandwidth to be larger than
modulation techniques using continuous phase modulations. Most machine
methods sample in the middle of a bit time to determine the value encoded,
so the symbols can be rounded to raised cosine shape without harming the
ability to decode the signal. But you can't do that with OOK Morse because
the information is encoded in those sharp timing edges, not in the signal
levels.
Symbol durations and spacings aren't uniform with OOK Morse either, so
finding a symbol center would be problematic even if it were useful to sample
there to decode the information being sent. Designing a matched filter for
OOK Morse transmissions of a priori unknown text is also impossible, but
is a commonplace technique for uniform codes. It is a proven fact of
communications theory that a matched filter is the best you can do,
and you can't do that with OOK Morse.
The use of uniform codes and phase continuous modulations allows far
superior performance to the use of Morse and OOK. The only claim to
fame of the latter is the simplicity of the equipment involved, but that's
traded against the greater operator conditioning required. That's often
the largest variable in the communications equation, ie the weakest
link of the system.
It is remarkable that it works at all, much less as well as it does.
With machine methods, that large variability is removed. The
machine works just as well regardless of the operator using it,
and machine methods can take advantage of better modulation
forms and codes that humans have difficulty using manually.
(Some say that takes the fun out of operating, I disagree, but
say it is their choice if they wish to handicap themselves in
that fashion.)
Is OOK Morse a digital mode? I don't think so. While it shares some
elements with digital modes, it is also different from them in important
ways. I think we have to classify it as an analog PWM baseband coding
using 2T AM modulation of the main carrier. It is a bandwidth and power
hog compared to some more modern methods (so is analog voice, of
course, and that doesn't stop us from using it if we choose).
It is a testiment to the remarkable pattern recognition ability of the
human brain that OOK Morse works at all. That's why machine
decoding of OOK Morse hasn't fared so well. We don't yet have
machines with the particular sort of pattern recognition abilities
of the human mind. However, if we strictly define the patterns we
intend to use in accordance with sound communications theory,
as we do with the better digital methods, then machine methods
can far outstrip the human brain as modem.
That's not because machines are smarter. It is because they can
use codes and modulations superior to OOK Morse while the human
brain has difficulty handling the patterns produced by those codes
and modulations manually. Our mental pattern recognizers, flexible
though they are, aren't optimized for the sorts of signals which
perform best in noisy or interference laden channels.
Gary
Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
------------------------------
Date: Sun, 02 Jul 2000 16:42:15 -0700
From: "Dana H. Myers K6JQ" <Dana@Source.Net>
Subject: CW versus hi speed digital etc.
To be continued in digest: hd_2000_178E
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