Looking at the scope picture of a single Morse dit at G4AON's
site http://www.astromag.co.uk/k3/k3_envelope2.jpg indicates
the trailing edge might be a bigger contributor to potential
clicks than the leading edge of the waveform. Note the upper
right corner has a fairly "sharp" transition from "on" to
"falling" and compare that to the nicely shaped transition at
the upper left corner.
>From all reports the K3 is more than acceptable but if any
additional effort is put into CW shaping, the "upper right"
transition may be a place to look.
73,
... Joe, W4TV
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Brian Alsop
> Sent: Sunday, March 30, 2008 11:01 AM
> Cc: elecraft@mailman.qth.net
> Subject: Re: [Elecraft] K3 CW rise time mod - Definition
>
>
> For what it is worth, I've just completed a Fourier analysis of the
> original K3 and revised K3 waveforms presented by G4AON on
> his website.
>
> I was a bit concerned that the sharpening of the leading edge would
> adversely affect bandwidth and possibly generate clicks.
>
> Bottom line for the region of the spectrum between 0 and +/- 200 Hz
> there is a slight increase in average power (maybe 3 db) for the new
> "sharper" waveform. In the range of 200 to 300 Hz the average power
> increases maybe 10 db. However at this point the spectral energy is
> down 50 db anyhow. Beyond this 350 Hz, the spectrum energy of the
> "sharper" waveform actually falls off relative to the 8ms case.
>
> These conclusions are "eyeball averages" of the sawtooth
> looking output
> produced. The teeth go above and below the zero db level.
>
> I was pleasantly surprised. Apparently it isn't all in "rise
> time" it
> is also how that waveform is shaped.
>
> Here are the assumptions/limitations of the analysis.
> 1) Code used "Fast Fourier Transform" by M.F. Hajen
> 2) A single dit was modeled.
> 3) Both dits had the same length in the model (about 70ms
> representing
> about 20 wpm).
> 4) Waveforms were digitized in 1 ms steps.
> 5) The assumption that the waveforms given represented
> voltage and hence
> db was calculated by 20 log (amplitude/amplitude at 0 Hz)
>
> This doesn't reflect repeating dits or CW made up of dots and
> dashes.
> However, it is probably a worse case analysis or close to it.
> I don't have a web site to post on. There is a .jpg file
> available of
> results.
>
> Disclaimer
> I'm not an expert on this or on using the calculational tools. The
> output does at least agree with the position of the first zero point
> predicted by a sinx/x formula for a single pulse of near
> infinite rise
> time and same width. Clearly it doesn't represent other
> effects in the
> rig which affect spectrum.
>
> Like a lawyer once said: "I'm giving you some free advice, it
> is worth
> every penny paid for it"
>
> 73 de Brian/K3KO
> .
>
> Paul Christensen wrote:
>
> >> I would like to see someone please take this discussion
> one step
> >> further and define the terms "hard" keying and "soft" keying, and
> >> describe how either an operator or someone listening would
> be able to
> >> discriminate between the two.
> >
> >
> > Gary, this topic has been covered in great detail in nearly
> every ARRL
> > Handbook for at least the last fifty years -- as well as other
> > publications. Some of the most relevant material is covered in
> > articles during the '40s and '50s by By Goodman and George Garmmer.
> > Not all of the material pertaining to "optimum key-shaping" is
> > accurate, but otherwise, the content is still accurate.
> >
> > Many of us do not like to be held hostage to one rise/fall
> setting as
> > a "one size fits all" answer to our operating practices. With
> > DSP-generated raised-cosine key shaping, it's now possible
> to tighten
> > up key shaping at high CW speeds without appreciably consuming
> > additional bandwidth.
> >
> > Paul, W9AC
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