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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