> If the goal is to copy the signal as best as possible at the highest
> speed possible while not disturbing others, then the ARRL's
> waveform is certainly not ideal.
I would agree with that and to simultaneously meet these two requirements,
the sine rise - sine decay in ~ 2 mS time on each slope is probably a good
starting point.
> Such a response can be likened to a 10Hz to 10,000Hz response
> on a SSB transmitter.
The waveform that I referred to in the 1998 ARRL Handbook is certainly not
the best for intelligibility, primarily due to the long decay which leads to
the bell-like characteristic. Again , the sine rise - sine decay would be
most appropriate. And, the Ten-Tec Omni V and early Omni Sixes come pretty
close, but not quite.
> It might stir "warm and fuzzy" feelings in
> some people, but it wastes spectrum and does not add to
> readability.
Yeah Tom, but the keyed waveform I referred to does sound awfully good
particularly from a clean oscillator, albeit at the expense of some
additional bandwidth. Sure, It's an aesthetics v. efficiency tradeoff but I
can live it and in my opinion it's not excessive if the rise/fall is ~ 2
mS. Anyway, I let you know where I'm parked before the next contest.
>
> > 10K control pot with a fixed resistor in its place. On the other hand,
> > the keying on a stock Yaesu FT-1000D sounds much too soft (yes, yours
too
> > Tom). But the FT-1000MP is just the opposite.
>
> Yet people who copy me near the noise floor always report no
> change in readability when I go to a hard clicky waveform in blind
> tests. So why should I click if it doesn't help signal readability?
> That's the same reason I won't use a 3.5kHz SSB filter.
Perhaps the majority cannot discern the difference but I sure can. When
fading becomes problematic or there's a high level of QRN, I can copy a
hard-keyed signal much better.
>
> It makes me believe that
> > little thought is given to the keyed wave-form in today's transceivers
> > when they gladly accept any result even if it varies wildly from one
> > generation of transceiver to the next...especially within the same
> > manufacturer. The mind-set appears to be "why bother with CW keying
> > improvements when that cost can be spent on adding more useless
features."
>
> Not so. The slope of the waveform at any point controls bandwidth.
> I can have a 2mS rise and fall that clicks like hell 5 kHz away, and
> I can have one that is not bothersome at all 500Hz away.
Right. The shape of the edge *together* with the ramp time contribute to
the bandwidth. For example, within a 2 mS ramp time, if the initial 1 mS of
the leading edge is near vertical, but the remaining 1 mS is a sine slope,
then there's an awful lot of occupied bandwidth. I see this at low power
amplifier levels when I'm using my Alpha PA-70V amp with three-state
electronic bias. It's almost as if the beginning of the leading edge is
hot-switched then ramps fine. Here. it's the bias circuit, not hot
switching that creates this and yes, clicks are heard.
> If the problem in the Ten Tec is only caused by ALC reducing
> limiting rise time, it could be easily cured by adding an external
> negative FIXED ALC voltage to reduce gain.
Unfortunately, Ten-Tec's fix was a bit more complex and invasive. To un-fix
it, I decided to change the ALC circuit. The negative ALC solution is a
good one for the earlier production units.
> > edition of QST. (See pp. 11-15, 166). George developed a unique keying
> > circuit in that two controls are brought out from the transmitter to
> > *separately* adjust the wave-form rise and decay time. Keying could
then
> > be adjusted to conform to band conditions. Limits placed on both
controls
>
> Unless George filtered the bandwidth of the applied keying
> waveform in a low-pass filter, he did not secure minimum bandwidth
> for a given rise and fall.
I don't believe minimizing bandwidth was his goal. The article addresses
the need good wave-form articulation while keeping clicks to a minimum. I'm
not sure how feasible a sine rise - sine decay circuit would have been in
1966.
> There is also a second problem that is almost always overlooked.
> Some rigs switch into transmit while the synthesizer is still moving
> to a new frequency, while others switch before the thing even
> moves! One popular high-end DSP rig does that, you can tell them
> in pile ups because they are the rigs that thump on top of the DX
> station when they are working split frequency.
Mine suffers from the same. The larger the offset, the worse longer the
synthesizer settling time. Splits greater than 10 kHz in CW sound awful and
chirp like crazy.
-Paul, W9AC
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