New ideas in CW
Fri, 12 Nov 1999 18:35:50 -0500
Rik Strobbe wrote:
> Visual-CW (or slow-CW or QRSS) has become a rather popular mode on LF.
> It has 2 very important advantages :
> 1. signal far beyond the audible 'triggerlevel' are detectable, allwing
> QSO's that would have been not possible with any other mode
> 2. is has a very narrow bandwidth, signals only a few Hz apart can easily
> be separated
> The main disadvantage is the transmission speed as the most elementary QSO
> takes already half an hour.
> I have been thinking about the possibilities to enhance the transmission
> speed without reducing the advantages of visual CW and did some mind (or
> paper) experiments :
> Assume the following (very basic) QSO :
> - CQ ON7YD K
> - ON7YD G3XDV K
> - G3XDV OOO K
> - ON7YD OOO TU K
> - GL SK
> At a speed of 3 seconds per dot this QSO will take 27 min. 42 sec.
> (assuming no 'time-loss' between the transmissions).
> Since visual-CW is derived from 'normal' CW we use the same morse code that
> was optimized for reception by ear. It has also some 'built-in
> intelligence' as the most frequent characters are short, but for visual-CW
> where mainly calsigns are exchanged (where the character-distribution is
> rather random) is this not so important. An important advantage of morse
> code is that we easily can 'decode' it visualy. Most of us would need a
> kind of translation-tabels for visual decodation of any other (eg. ASCII)
> code, what is not so convenient.
> Without abandoning the morse code and the way of visual decoding we are
> used to so far, some time can be won by reducing the dash/dot ratio from
> 3/1 to 2/1.
> While this 3/1 ratio is very essential for decoding by ear there is no real
> advantage of the 3/1 vs. 2/1 ratio in visual decoding, the signal is
> perfectly 'readable', it just looks a bit odd.
> But what do we win ? The above QSO, still at 3sec. per dot but with a 2/1
> dash/dot ratio would take 22 min. 24 sec, a gain of 5 min. 18 sec. or an
> increase in speed of 24%.
> The advantage is that only minor changes are involved, but there is only a
> limited gain.
> Another alternative is replacing the discrimation of dashes and dots from
> the time-domain to the frequency domain. This would mean that 'dashes' and
> 'dots' have the same length (3 seconds) but that they are transmitted on
> different frequencies. Since in visual-CW the frequency discrimination is
> very high a shift of 5Hz (or even less) is sufficient. Using this technique
> we do not need the 'time-gaps' between the dashes and dots, only between
> characters we would need a 'time-gap' of 1 dot and a 2 dot 'time-gap'
> between words.
> Using this system the above QSO will take only 9 min. 27 sec., a gain of 18
> min. 15 sec or increase in speed of 293%.
> As the frequency is now used to disciminate 'dash' and 'dot' the
> transmitter need a sufficient frequency stability. But for a 5Hz shift a
> 2Hz stability should be sufficient and this is not more difficult to
> achieve on 136kHz as a 50Hz stabilty on 80m or a 400Hz stability on 10m.
> The next question was how easy (or difficult) our eye will translate the
> frequency-shifted signals to 'dashes' and 'dot' (and so to characters).
> Therefore I wrote a small program that at randum generated CW characters
> and showed them on screen as discribed above. At a speed of 3 sec. per dot
> I could easily decode the characters even without using pencil and paper.
> Even if there was a sequence of 'O-M-T' or 'H-S-I-E' decoding was possible
> al long as there were some other characters arround.
> We will need to adapt both our equipement (to FSK) and our mind if we want
> to use this technique but the adavantage is a significant increase of the
> transmission speed (ca. 300%).
> 73, Rik ON7YD