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PA2AGA > HDDIG 06.07.00 02:10l 185 Lines 7233 Bytes #-9409 (0) @ EU
BID : HD_2000_180C
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Subj: HamDigitalDigest 2000/180C
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From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Wed, 05 Jul 00 21:28:04 MET
Message-Id: <hd_2000_180C>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
as 18 dB below the noise in a 500 Hz rectangular receiver bandwidth. In both
cases, it is the use of matched filter techniques which bring these inaudible
signals up to a positive Eb/No.
Matched filter technique cannot be applied to CW because the waveform
has no a priori known spectrum when unknown text is sent. (If you know the
message that is to be sent, you can form a matched filter for the
transmission,
but then if you already know the message contents, the point of receiving it
becomes moot in most cases, EME operations not withstanding.)
>I agree that most CW is conducted using simple OOK, but so what. To be
>fair in a comparison then all other modes should use the same modulation.
>If they can use more advanced modulation, then there is no reason why CW
>cannot do so as well.
If you did, it would no longer be CW. The term CW encompasses the character
encoding, the baseband coding, and the modulation method. Take any one of
those away, and you no longer have CW. But granted that, Morse is still an
edge timing code with non-uniform symbols, and that puts it at a disadvantage
to uniform codes which aren't edge sensitive.
Skilled manual operators do make CW work remarkably well, but that's despite
the method's shortcomings, not because of them. Machine methods, which are
as you say not as powerful in some respects as the human brain, still perform
better because they are used with codes and modulations which are so much
better than CW that the machine's limitations are overcome by the superiority
of the coding and modulation techniques it can use.
It isn't just a matter of cost that has caused commercial and military
communications to abandon CW (though the costs of maintainng an
adequate CW capability are significant). It is more importantly a matter
of performance. CW just isn't as good as some of the more modern
techniques.
This isn't "trashing" CW. It is just a recognition of its design limitations.
Like analog voice, which has even more severe limitations, we may
continue to use CW if we like. But it is a mistake to try to claim for
it a superiority that it does not enjoy in fact.
Gary
Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
------------------------------
Date: Tue, 4 Jul 2000 12:14:19 -0500
From: "Peter O. Brackett" <ab4bc@ix.netcom.com>
Subject: CW versus hi speed digital etc.
Gary:
As you noted, it is indeed possible.
Applications?
Gary... it's Official Secrets Act stuff...
if I told you where, why, and when it is done, I'd have to kill you
afterwards...
.. as it is I've probably told more than I should.
Peter K1PO
"Gary Coffman" <ke4zv@bellsouth.net> wrote in message
news:dn04msk1ie902vrsq6ij9637h1t3emsi6h@4ax.com...
> On Sun, 2 Jul 2000 02:57:53 -0500, "Peter O. Brackett"
<ab4bc@ix.netcom.com> wrote:
> >Forward Error Correction (FEC).
> <snip>
> >Hamish clearly as you, or someone else, pointed out up the thread
> >"conventional" CW uses simple on off keying (OOK) of a single carrier as
the
> >conventional method of modulation.
> >
> > And so... clearly CW operators cannot and have not done bandwidth
> >efficient (integrated coding and modulation) FEC...
> >
> > Now on the other hand for the much older and traditional approach to
FEC,
> >where coding and modulation are separate, many skilled CW operators and
> >their communications administrators have in the past, and can easily add
the
> >first method of FEC to their transmissions.
> >
> >In fact many commercial CW operators and certainly most military CW
> >operators use FEC. This usage of FEC over CW began in WWII, "the big
one"
> >and has been in use continuously since then.
> >
> >Of course you won't have heard it on the air in "plain language", but I
can
> >send you to several HF frequencies where you may copy on air CW FEC,
> >generally in the format of "five letter code groups".
> >
> >In fact, unlike for amateur radio examinations where the testing for CW
> >prowress is done in plain language, for commercial and military sending
and
> >receiving CW tests, the tests invariably include/included code groups,
many
> >of which are/were FEC encoded.
>
> Ok, I'm interested. What FEC algorithm is used with these code groups?
> AFAIK code groups are only used to obscure meaning, and don't include
> cross products and other redundancies designed to locate and correct
> transmission symbol errors as part of their design. Note that I don't
doubt
> that such error detecting and correcting block coding *could* be done for
> CW transmissions, but I've never heard of it actually being done in
practice.
>
> Gary
> Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
> 534 Shannon Way | We break it |
> Lawrenceville, GA | Guaranteed |
------------------------------
Date: Tue, 4 Jul 2000 12:40:14 -0500
From: "Peter O. Brackett" <ab4bc@ix.netcom.com>
Subject: CW versus hi speed digital etc.
Gary:
You are getting reckless with the truth now...
I'll go through the post below by "snippets" for you...
[snip]>
> CCW technique, which is different from CW, does use fixed clock timing,
though
> it doesn't use uniform symbol timing (it can't, because the symbols aren't
uniform).
> The information is still encoded in the symbol edges, which are harder to
detect than
> the mere presence or absence of signal.
>[snip]
The symbol edges ARE uniform. There are only three Morse Code Symbols, the
dot, the dash and the space. When transmitted in time, they are usually
synchronous with a "dot" clock. i.e. the basic Unit Interval of Morse is
the length of the dot, the dash is three dot's in length and the space is
one dot in length. Morse is a comma free code, synchronous in time with all
the "edges" lined up exactly on the "dot" clock, the only ambiguity in
timing would be considered a "jitter" due to inacurate clocking resulting
from human hands. The timing "jitter" or the timing itself encodes no
information.
I repeat again for clarity, Morse is a three level code, it consists of just
three symbols, the dot, the space and the dash, call them A, B & C or X, Y &
Z, no matter what you call them there are still only three.
Gary, count em, ddot, space, dash, 1, 2, 3... one can construct any Morse
message from just those three symbols alone an none other. So there...
Inter-character and word spacing are symbols, as we know, in the rendering
of plain language texts such as written English, these symbols are not
present in Morse, rather they are encoded into Morse using the three Morse
symbols. for instance, the Inter-character space [white space symbol] is
encoded in Morse by a Morse space symbol, the inter-word space symbol
[another white space symbol] is encoded by thee Morse space symbols. And
the "new line symbol [carriage return line feed symbol concatenation] are
encoded by the Morse sequence [AA or didah didah]
dot-space-dash-space-space-space-dot-space-dash]
To be continued in digest: hd_2000_180D
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