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PA2AGA > HDDIG 03.07.00 23:59l 166 Lines 6895 Bytes #-9412 (0) @ EU
BID : HD_2000_178F
Read: GUEST
Subj: HamDigitalDigest 2000/178F
Path: DB0AAB<DB0PV<DB0MRW<DB0SON<DB0ERF<DB0SHG<DB0SM<PI8DAZ<PI8GCB<PI8HGL
Sent: 000703/1846Z @:PI8HGL.#ZH1.NLD.EU #:58002 [Den Haag] FBB $:HD_2000_178F
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Mon, 03 Jul 00 19:07:58 MET
Message-Id: <hd_2000_178F>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
> 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 19:58:48 -0500
From: CAM <W6RCA@mindspring.com>
Subject: CW versus hi speed digital etc.
"Peter O. Brackett" wrote:
> It is so advanced in it's design concepts that it is not even a simple
> binary system, in fact it is a multi-level digital logic code.
111010101000101000111010001011100010111010001110101110111 :-)
--
http://www.mindspring.com/~w6rca
------------------------------
Date: Mon, 03 Jul 2000 09:33:51 +0300
From: Paul Keinanen <keinanen@sci.fi>
Subject: CW versus hi speed digital etc.
On Sun, 02 Jul 2000 19:58:48 -0500, CAM <W6RCA@mindspring.com> wrote:
>"Peter O. Brackett" wrote:
>> It is so advanced in it's design concepts that it is not even a simple
>> binary system, in fact it is a multi-level digital logic code.
>111010101000101000111010001011100010111010001110101110111 :-)
Binary systems usually attach some kind of weight (e.g. 1, 2, 4, 8 ..)
to each binary digit. The sequence above is a combination of pulse
width and pulse position modulation (that would be V1A designation
instead of A1A :-), producing 5 different symbols, that are used to
code the character set. So conceptually, this is quite similar to the
EFM (eight-to-fourteen modulation) used in CDs, which produces 267
usable symbols from a 14 time slot sequence.
Paul OH3LWR
------------------------------
Date: Mon, 03 Jul 2000 07:54:59 GMT
From: hamish@cloud.net.au (Hamish Moffatt VK3SB)
Subject: CW versus hi speed digital etc.
Peter O. Brackett <ab4bc@ix.netcom.com> wrote:
> I certainly respect your desire, and today your right, not to have to
> develop the skills to copy CW manually at high speeds.
I don't have any particular grudges there. I have a full unrestricted
license here in Australia, for which I took two exams: one of receiving
5 minutes of solid copy, and one of transmitting 2.5 minutes worth,
both at 10 WPM.
I confess that if I didn't have to learn it, I probably wouldn't have.
I do find it useful on occasion though (repeater/beacon identifications
if nothing else). I may try it on the air one day.
> As a keyboard QSO'er yourself, and not necessarily a CW affecionado, which
> do you think is the harder skill to develop, in terms of [As aircraft pilots
> are fond of saying.] the "stick time" required?
Both come readily with steady practise I'm sure. I've done that
practice at the keyboard for sure.
> I say, if we take CW skill testing out of the amateur examinations, that we
> replace it with an in depth theoretical and practical test of knowledge in
> the digital communications arts, beginning with the theoretical background
> for CW's effectiveness and leading upwards from there...
I agree. Having said that, I wonder if it's too much to ask
on the license exam.. the theory is not exactly trivial I'm sure
you'll agree.
Hamish
--
Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>
------------------------------
Date: Mon, 03 Jul 2000 08:04:08 GMT
From: hamish@cloud.net.au (Hamish Moffatt VK3SB)
Subject: CW versus hi speed digital etc.
Peter O. Brackett <ab4bc@ix.netcom.com> wrote:
> Also... from a channel coding and modulation viewpoint, CW can easily be
> transmitted using a variety of modulations from FSK to PSK, to whatever. It
> just then makes direct copy of the sound "by ear" less familiar to
> operators, a conversion device to convert back to a keyed tone would suffice
> for human readability.
To be continued in digest: hd_2000_178G
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