I think most of the high speed, QRQ, crowd would agree that when speeds get
up over 50wpm, the weight needs to be reduced otherwise, the characters run
together in one's head. I can copy 50wpm as long as the signals is decent
and weight is light but is someone is sending with "normal"weighting, it
starts running together.
This makes sense to me since with less weight, there's more space between
characters. Also this helps compensate for filter ringing which tends to run
high speed code together. Try copying 50wpm through a narrow xtal filter,
it's not easy!
As for hard keying. Again, there's more space between characters with a
steeper waveform BUT with more sidebands, a weaker signal will be influenced
more by selective fading. The phase distortion that occurs due to those
sidebands can result in even more difficult copy. So I think we have a catch
22 here. Hard keying is easier to copy at high speeds but more distored by
fading.
Steve Ellington
N4LQ
----- Original Message -----
From: "Paul Christensen" <paulc@mediaone.net>
To: <W8JI@contesting.com>; <tentec@contesting.com>; <WA3FIY@radioadv.com>
Sent: Sunday, February 03, 2002 7:37 AM
Subject: Re: [TenTec] Pegasus/Jupiter keying - In search of Perfect CW :-)
> > I don't know where the rumor comes from that excessive bandwidth
> > somehow results in "cutting QRM or QRN" better. It certainly is not
> > based on any type of engineering or research!
>
> I'm not sure of the methodology, but I recall a graph from a Navy study
in
> which keyed envelope shape rise/decay was plotted against minimum
> discernable signal strength. Another graph depicted CW speed against MDS
> conditions as well...and a third graph combined both factors. I'll look
for
> this...
>
> >From my own experience, I know that I can copy harder keyed waveforms in
MDS
> conditions at relatively high CW speed, than softer waveforms. Clearly,
my
> own error-free reception is a function of 1) CW transmission speed and 2)
> the keyed waveform shaping. I do not believe you can have this
discussion
> without addressing these two factors together. For example, if the
> transmission speed is ~ 5 WPM (traditional, non Farnsworth), I would
expect
> that little difference would be detected in the copyability between hard
and
> soft keyed waveforms.
>
> Another interesting source is found in my 1998 ARRL Handbook on page 15.7:
>
> "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. If
> the transmitted signal will be subjected to propagation fading - a safe
> asumption for any long-distance radio communication - we harden our keying
> by making the transmitter's output rise and fall more quickly. This puts
> more energy into more keying sidebands and makes the signal more copiable
in
> the presence of fading - in particular, selective fading, which linearly
> distorts a modulated signal's complex waveform and randomly changes the
> sidebands' strenght and phase relative to the carrier of each other. The
> appropriate keying hardness also depends on the keying speed (W9AC: there
it
> is...). The faster the keying in WPM, the faster the on and off times -
the
> harder the keying must be for the signal to remain ear-readable through
> noise and fading...A transmitter's CW waveshaping is therefore usually
> hardwired to values appropriate for reasonabley high-speed sending (35 to
55
> WPM or so) in the presence of fading. As a result, we generally cannot
vary
> keying hardness at will as we might vary a voice transmitter's modulation
> with a front panel control (W9AC: two notable exceptions include Kachina
and
> Kenwood's menu-selectable DSP-based CW waveform generator). Rise and fall
> times of 1ms to 5ms (5ms rise and fall times equate to a keying speed of
> 36WPM in the presence of fading and 60WPM if fading is absent) are
common."
>
> Arguably, perhaps the best solution allows: 1) variable control of the
keyed
> rise/fall time from a front panel control, or 2) a circuit in which the
> speed of the waveshape changes as a function of keying speed. In order to
> accomodate hand keys and external keyers, the keying input would require
> analyzing...which may result in additional delay from the time of the
keying
> until RF is generated. In contest conditions, the front panel control can
> be set to "soft" and for other band conditions, depending on propagation
and
> crowded condition, the control could be set between the hard and soft
> extremes.
> 73,
>
> -Paul, W9AC
>
>
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