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PA2AGA > HDDIG 06.07.00 02:10l 197 Lines 7270 Bytes #-9409 (0) @ EU
BID : HD_2000_180D
Read: GUEST
Subj: HamDigitalDigest 2000/180D
Path: DB0AAB<DB0SL<DB0RGB<DB0MRW<DB0ERF<DB0BRI<DB0SM<PI8DAZ<PI8GCB<PI8HGL
Sent: 000705/2113Z @:PI8HGL.#ZH1.NLD.EU #:58936 [Den Haag] FBB $:HD_2000_180D
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Wed, 05 Jul 00 21:28:12 MET
Message-Id: <hd_2000_180D>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
[snip]
> One of the problems here is the use of the term "CW". Conventionally that
> means use of Morse Code by on-off keyed baseband symbols which are
> then impressed on a constant carrier by 2T AM modulation. Anything else
> is no longer CW. It would be helpful if you are a bit more precise when
you
> talk about the character encoding, the baseband modulation, or the
> transmission modulation so that we can know what you mean.
[snip]
Gary lets not get pedantic, CW is an acronym and it actually stands for
Continuous Wave. As you well know, Morse is definitely not a continuous
wave, in fact a "real" continuous wave is a mathematical fiction, not
possible in nature.
So ... Gary it is not me, but the folks who trash CW by making silly apples
to oranges comparisons between Morse [CW] and the other digital modes who
are imprecise!
[snip]
> No, I disagree. CW encompasses all of the items I listed above.
> That is not a digital system. Taken individually, some of the elements
> of CW might be considered digital, but taken as a whole CW is not
> a digital transmission mode.
>[snip]
Gary you are entitled to disagree, that's your "right" but that does not
make you right!
[snip]
> Actually, Morse is a quintenary code. It has five symbols, the dot, the
dash,
> the intracharacter space, the intercharacter space, and the word space.
> When conveyed using OOK AM (aka CW), the latter 3 symbols aren't voiced,
> and have to be inferred against the noise background. That reduces the
> probability of correct detection substantially.
[snip]
Wrong! Gary, Morse is ternary, see my comments and example encodings above
[snip]
> Varicode is one of the shortcomings of PSK31. It limits the ability to do
> context free FEC compared to the usage of a uniform length code. The
> fact that the most used letters are sent with the least amount of
transmission
> symbol information makes the probability of errors higher than for uniform
> length codes. It does save transmission time, but at the cost of a higher
> probability of uncorrectable errors. Conventional Morse coding suffers
> from this same problem, and when used with OOK AM, additionally doesn't
> voice some of the symbols at all. At least PSK31 voices all of its
transmission
> symbols (one reason it'll work at signal levels where conventional CW
> operators can't even detect the presence of a signal at all.)
>[snip]
Not true, Shannon showed in both his landmark 1948 Proc. IRE paper and his
subsequent 1958 paper the rationale for source coding and channel coding and
their respective roles in communications efficiency, I'll pass the
references to you for your perusal, such a subject cannot be easily expouned
in the limited time available to those of us who kibbitz on Usenet NG's.
[snip]
> You are incorrect. I've devoted much more study to digital communications
> than I have to antennas.
>
> >And besides, my friend, heh, heh you'r spoiling my fun here on this
> >thread...
>
> That's what I do best.
[snip]
Gary my friend there is no doubt that you are "well informed".
But your knowledge of this area apparently includes some "holes" and a
little bit of fuzzy thinking.
"A little knowledge is a dangerous thing, but drinking deeply of that...."
Lord Byron
And so... Gary I ask you not to trash CW until you learn a little more
about digital communications.
Best Regards,
Peter ["CW is digital"] K1PO
------------------------------
Date: Tue, 4 Jul 2000 13:07:09 -0500
From: "Steve Sampson" <ssampson@usa-site.net>
Subject: CW versus hi speed digital etc.
> Peter ["CW is digital"] K1PO
There's nothing worse than Yankee's in Alabama...
------------------------------
Date: Tue, 04 Jul 2000 13:25:58 -0500
From: CAM <W6RCA@mindspring.com>
Subject: CW versus hi speed digital etc.
Gary Coffman wrote:
> 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.
In the implementation that I observed, each 'dot' time was sampled in
the middle of the 'dot' time and converted to a binary '1' or '0'.
--
http://www.mindspring.com/~w6rca
------------------------------
Date: Tue, 4 Jul 2000 13:33:26 -0500
From: "Peter O. Brackett" <ab4bc@ix.netcom.com>
Subject: CW versus hi speed digital etc.
Gary:
[snip]
> That's simply not true. The best known contemporary illustration that it
is
> not true is PSK31. Time and again operators demonstrate the ability to
> work PSK31 signals that are *inaudible* to the ear. PACTOR II also
illustrates
> the ability of well designed systems to work at signal levels that are as
much
> 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.
[snip]
Gary, tsk, tsk.. *inaudible* PSK-31, heh, heh. Don't give me that
stuff.... it's anececdotal hearsay based upon non-scientific observations.
Most folks "listen" to PSK-31 in a 2.4 kHz bandwidth, in fact you hear them
bragging of seeing several simultaneous signals in their digipan display,
but hearing nothing, heh,heh.
The reason they don't hear is because they are listening in a 2.4 kHz
bandwidth which lets in too much noise and interference which drowns out the
PSK signals, but the PSK-31 decoder is listening in a 100 Hz bandwidth
through it's digital filter [Matched filter, nearly.].
If the human listened in the same bandwidth it would be perfectly audible.
Jeesh, give me a break!
100 Hz bandwidth signals on the HF channel are very often inaudible in a 2.4
kHz bandwidth but perfectly audible in a much narrower bandwidth, [the
matched filter]!
Gary, unless you have done this, don't talk about it...
Simply copying a narrow band digital mode when you can't hear it in a wider
band means nothing, nothing nothing!
Gary.... Time and again CW operators have demonstrated their ability to copy
CW signals that are inaudible to the ear [Of a person listening in a 2.4 khz
bandwidth]. In fact I myself have personally done that many times.
I have often gone off frequency [QNY] on a CW traffic net in bad conditions
of QRM, QRN, etc... and passed 10 messages in 15 minutes with perfect copy,
under conditions when the average ham couldn't hear either of us. Because
me and the sending operator, zero beat each other and cranked in our 75 Hz
BW filters and hunkered down. Meanwhile a ham down the street who was
supposedly monitoring the frequency to pass more traffic to me [QRV], heard
nothing on our frequency and went back and so reported to the NCS... he
simply didn't know the exact frequency we were on and couldn't find us with
only his 2.4 kHz filter in line, he needed to cut his bandwidth way back to
100 Hz bandwidth to get us perfect copy! In this case the 75 or 100 Hz
was/is close to the matched filter for CW at 18wpm...
To be continued in digest: hd_2000_180E
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