ON7YD wrote:
DFCW is still a very experimental mode, so not very standardized yet.
Generaly accepted is that the higher frequency stands for 'dash' and the
lower for 'dot'. The frequency shift is dependent on the dot length. For 3
seconds per dot (that has become a kind of informal standard) a shift of
4Hz is used. A 1 second 'gap' is used to separate the elements (dots and
dashes) within a character, characters are separated by a gap of 1 dot
length, words by a gap of 2 dot lengths.
Rik,
Have I misunderstood, or are you saying there is a gap between
each dot and each dash? I thought there was no need to do this as
the frequency determines whether an element is a dot or dash so a
dot three times the dot lenght must be three consecutive dots.
Probably me being dumb.
Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm
Mike, a gap (even small) helps a lot to recognize a character.
After a discussion with Alberto I2PHD, we suggest a modified version
of DFCW, with, probably, an even higher resistance to QRM.
Let transmit three frequencies, the higher for the dash, the
middle for the dot, the lower (equally spaced) for the "key up".
The advantage is to always have a carrier, and being easier
to detect a space between characters in noise.
The output will be like:
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_ _ _
(use fixed spacing characters to see)
I try to attach a small ASCII file to this message; have a look, there is also
an example with the "space" frequency between dot and dash.
To modify the TX is very easy, at least for me; I will do some tests in this
way by next weekend. No modifications to existing QRS program are necessary,
only a manual RX/TX switch.
About the frequency difference, there are of course no fixed rules, but don't
be too wide. It's easier to see closely spaced signals, like 10 times the
resolution used by the receiving program. 1-2-4 Hz and/or multiples and
submultiples seems practical.
73, Marco IK1ODO
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Marco Bruno - IK1ODO
[email protected]
SPIN Electronics - www.spin-it.com
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