>
> W8JI:
>
> > The ideal shape is a raised sine wave shape, not the "perfect"
> > shape they show.
>
> I suppose it depends on your definition of the perfect wave shape. If
what
> you see is the same as my reference on p 15.6 of the 1998 ARRL Handbook, I
> would gladly trade my eye teeth for the waveform as represented in figure
> 15.8(a). This represents the classic grid-block keying waveform as used
> with simple single-pole R/C timing circuits. Here, the leading edge rises
> quickly and gradually decelerates until the final envelope is formed. The
> trailing edge falls quickly but then trails asymptotically to zero. It's
> this waveform that carries that plosive, bell-like sound that's so
> unmistakable through selective fading. I'm sure others will disagree:
> Ten-Tec believes that the perfect waveform is perfectly symmetrical. If
one
> views the keyed waveform of the Omni V or early Omni Six transceivers,
> you'll see a gorgeous, symmetrical wave-form. Later, in an attempt to
> reduce leading edge power spike, the ALC time was shortened which
> successfully cured the power spike, but left a sharp leading edge rise
time
> of 1 mS or less. Additionally, the integral CW wave-form adjustment
control
> became a useless feature as it had no control over the leading edge.
>
[snip]
Surely the "perfect" keying shape for any rectangular pulse train (for
that is what CW is) is a Gaussian? Not sin(x)/x or RC filtered?
I recall (just about) from comms lectures at University that a Gaussian
shapped pulse in the time-domain gives minimum occupied signal
in the frequency-domain, and FFT of a Gaussian shapped pulse is another
Gausian shapped pulse... and all that.
This being the case we could really set those Japanese software engineers
that develop radios with ever more fiddly and useless features some
*real* engineering to do... they've got super-powerful DSPs in most
modern radios - you'd think that could apply an appropriate filter/edge
to a rectangular pulse...
Never looked at what my JST245 does for keying waveform but it
sounds fine and has never given any problems but then its a 'proper'
radio.
Mike G8TIC
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