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Date: Thu, 13 Jul 00 23:50:55 MET
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Ham-Digital Digest Wed, 12 Jul 2000 Volume 2000 : Issue 187
Today's Topics:
CW versus hi speed digital etc. (2 msgs)
Forget HF & CW - Think Digital (16 msgs)
PSK31 (and other modes) questions (3 msgs)
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Loop-Detect: Ham-Digital:2000/187
----------------------------------------------------------------------
Date: Tue, 11 Jul 2000 21:58:45 GMT
From: kleing@NOSPAMqualcomm.com (Klein Gilhousen)
Subject: CW versus hi speed digital etc.
This is a pretty interesting thread for me. I have been a ham since I
was 13 and have spent most of my professional career in digital
communications, most recently (the last 15 years) as a co-founder at
Qualcomm.
In principal, OOK (CW) ought to be poorer in performance than PSK in a
Gaussian channel by a few dB. But we have anecdotes claiming that
human operators can match the performance of some of the digital
modes. How do we reconconcile this? One way is to consider that "in
principal" didn't consider the whole system involved in human decoded
Morse. In fact there IS an FEC system in Morse CW. It's called the
English (or whatever you speak) language. There is considerable
redundancy in the language and additional redundancy on the context.
A skilled human "decoder" can take advantage of all this context and
code and wring more out of a given situation than one might suspect.
In addition to FEC coding, there is feedback coding available. CW
traffic handlers developed methods for detecting errors and asking for
"fils" to make corrections. A further aspect of the system is rate
adaptation. The transmission speed can be adjusted to take advantage
of or accommodation to temporary changes in channel conditions.
I disagree with the notion that Morse CW is not or cannot be a digital
system. The key idea in what makes a digital system is that the
modulation system defines a number of discrete symbols that are sent.
Morse CW certainly qualifies on this count. Additionally, I have no
problem conceiving of a machine implemention of Morse CW that is every
bit as digital as the other modes which we have no problem accepting
as digital. Fully implementing all the implicit codes would be quite
a challenge, however.
Actually, we use FEC all the time in ham communications, i.e., the
phonetic alphabet. If one wishes to have an explicit FEC code in
Morse CW, it is a simple matter to encode the messages (mentally, it
you like) into the phonetic alphabet and transmit them this way. And
it is also a simple matter for the skilled human operator to mentally
perform the error detection and correction function. Does this work
as well as convolutional encoding/Viterbi decoding? Of course not.
But it does function as a FEC system, and one that can be implemented
by incredibly simple means.
By the way, I think that Morse CW is a binary modulation system (not
ternary or whatever). There are two signalling elements: transmission
of a dot length pulse, and a dot length silence. Everything else can
be described as a simple code combining sequences of these elements.
The code has certain rules, such as that there are no two dot long
pulses transmitted. This may sound pedantic but it is the way you
begin to describe how you would build an optimum receiver for Morse
CW. And yes, one can build a practical matched filter system for
Morse CW. Just because people usually don't doesn't mean one can't do
it.
I'm not trying to start arguments here, just bringing another
perspective.
Klein Gilhousen
Bozeman, MT
WT6G
------------------------------
Date: Tue, 11 Jul 2000 21:18:58 -0500
From: "Steve Sampson" <ssampson@usa-site.net>
Subject: CW versus hi speed digital etc.
That sounds like the most reasonable description to me...
It looks like pulse radar with poor leading and trailing pulse edges :-)
"Klein Gilhousen" wrote
>
[snip]
> By the way, I think that Morse CW is a binary modulation system (not
> ternary or whatever). There are two signalling elements: transmission
> of a dot length pulse, and a dot length silence.
------------------------------
Date: Tue, 11 Jul 2000 16:18:10 -0500
From: Jeff Goodspeed <cmsx42@email.mot.com>
Subject: Forget HF & CW - Think Digital
I like Will's position. I too feel the "magical" element of global
communication without using wires. I enjoy being at the "mercy" of natures
interactions of sun and ionosphere.
I also see a cultural element in this topic. Communication via the internet
implies a total dependence on society with the subjugation of the
individual in the act. No one can communicate from point A to point B via
the internet without tens of thousands of other people showing up to work,
keeping the multi billion dollar network humming. The internet communicator
hits the carriage return key which in turn grovels to the Internet Service
Provider for permission to have the puny little packet transported over the
behemoth. The sender of the information can take about as much pride in
completing the communication as he can in forcing the sun to rise in the
east each morning.
Point to point radio communication on the other hand is more an expression
of rugged individualism. The radio operator is in control of the
communication process and only needs the cooperation of the receiving party
to complete the transaction. Entire societies can rise and crumble without
impacting two individuals communicating via radio.
Which of these two would give you something to feel pride in?
Will wrote:
> Except the Internet is not radio, and it is not a radio. After all this
> time, radio is special and "magical" because, look 'ma, no wires! That
> my signal travels from my antenna to that of another ham on the other
> side of the world using nothing made by man still amazes me. And in
> order to make efficient and reliable use of radio, one has to learn
> about and monitor weather--both the terrestrial and solar varieties. It
> isn't the same as the internet at all, and can't be. For all the touted
> reliability and ease of internet communications, it doesnt take the
> place of radio as a science and hobby. It takes the place of the
> telephone, actually. The internet is wonderful, but it doesnt replace
> radio--the mistake is that the sole, or even primary goal of ham
> communications is to talk at will to a specific other person without
To be continued in digest: hd_2000_187B
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