[Elecraft] Hearing CW - Fundamental Keying Waveform?

[Ramakrishnan Muthukrishnan]

For the mathematically inclined, here is another link:

http://fermi.la.asu.edu/w9cf/articles/click/index.html

Ramakrishnan

On 9/20/06, Ramakrishnan Muthukrishnan <vu3rdd at gmail.com> wrote:
> Thanks Dan for copying me. I just subscribed to the list.
>
> The issue is discussed at length by Doug Smith, who is also the Editor
> of ARRL's QEX.
>
>    http://www.doug-smith.net/cwbandwidth1.htm
>
> In the digital communication world, we have a baseband modulation
> scheme called Pulse Amplitude modulation (PAM), which is one of the
> simplest form of modulation. CW can be thought of as one form of PAM.
> To avoid Inter Symbol Interference (ISI), the pulse shape used in the
> PAM scheme should have certain properties. Key Clicks are nothing but
> abrupt changes in the waveform, which interferes with the neighbouring
> pulse shapes, which is ISI. The Sinc Pulse is one such waveform, but
> is difficult to synthesize in real world. Another such pulseshape
> which satisfies this is the Raised Cosine waveform.
>
>  http://en.wikipedia.org/wiki/Raised-cosine_filter
>
> Another variant is the square root of raised cosine shape, where
> transmitter and reciever both use a square root of the above filter
> response in (frequency domain) and when you convolve them together in
> time domain you get the raise cosine response.
>
> I think I have complicated it too much. :-(  The above links explain
> it in a much better way.
>
> This is the basic principle behind it, but there are many refinements.
>
> Ramakrishnan, VU3RDD
>
> On 9/20/06, Dan KB6NU <kb6nu at w8pgw.org> wrote:
> > This discussion is very interesting to me. I hate copying stations
> > whose keying isn't sharp enough. The dits and dahs seem to blend
> > together. It seems to me that with all the DSP power that modern rigs
> > have, there should be a way to "sharpen up" a CW signal to make it
> > more intelligible. I'm copying this message to my friend VU3RDD, who
> > is a DSP engineer, to see what he might think about this.
> >
> > 73!
> >
> > Dan KB6NU
> > ----------------------------------------------------------
> > CW Geek and MI Affiliated Club Coordinator
> > Read my ham radio blog at www.kb6nu.com
> > LET'S GET MORE KIDS INTO HAM RADIO!
> >
> >
> > On Sep 20, 2006, at 12:31 AM, Don Wilhelm wrote:
> > > Darrell,
> > >
> > > That has ben dropped from the more recent handbook (does not appear
> > > in my
> > > 2005 edition).
> > > I am going 'out on a limb' here by saying that this stems from the
> > > concept
> > > that 'some keyclicks are good' philosophy.  Sidebands on a CW
> > > signal are the
> > > result of the keying shape, and there is more to it than just the
> > > rise and
> > > fall times - there is the rounding at the corners to consider too.
> > >
> > > I have heard many an operator state that 'hard keying' will get you
> > > through
> > > a pile-up better.  While that may be true, it certainly is not
> > > 'neighborly'.
> > >
> > > I am glad to see that this statement does not appear in the more
> > > recent
> > > handbooks.
> > >
> > > 73,
> > > Don W3FPR
> > >
> > >
> > >> -----Original Message-----
> > >> From: elecraft-bounces at mailman.qth.net
> > >> [mailto:elecraft-bounces at mailman.qth.net]On Behalf Of Darrell
> > >> Bellerive
> > >> Sent: Tuesday, September 19, 2006 6:08 PM
> > >> To: Elecraft List
> > >> Subject: [Elecraft] Hearing CW - Fundamental Keying Waveform?
> > >>
> > >>
> > >> The recent thread on filter settings and hearing reminded me of a
> > >> question I
> > >> would like to get an answer to.
> > >>
> > >> In the ARRL 2001 Handbook on page 15.7 we find:
> > >>    "The dots and dashes of a CW signal must start and stop
> > >> abruptly enough so
> > >> we can clearly distinguish the carrier's presences and absences
> > >> from noise,
> > >> especially when fading prevails. The keying sidebands, which sound
> > >> like
> > >> little more than thumps when listened to on their own, help our
> > >> brains be
> > >> sure when the carrier tone starts and stops.
> > >>    It so happens that we always need to hear one or more harmonics
> > >> of the
> > >> fundamental keying waveform for the code to sound sufficiently
> > >> crisp."
> > >>
> > >> What is meant by "the fundamental keying waveform"?
> > >>
> > >> How do we take "the need to hear one or more harmonics of the
> > >> fundamental
> > >> keying waveform" into account when setting up the IF and audio
> > >> filters?
> > >>
> > >> 73,
> > >>
> > >> Darrell  VA7TO  K2 #5093
> > >>
> > >> --
> > >> Darrell Bellerive
> > >> Amateur Radio Stations VA7TO and VE7CLA
> > >> Grand Forks, British Columbia, Canada
> >
>
>
> --
>   Ramakrishnan - VU3RDD
>


-- 
  Ramakrishnan - VU3RDD